Ticket Allocation Optimization of Fuxing Train Based on Overcrowding Control: An Empirical Study from China - MDPI

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Article
Ticket Allocation Optimization of Fuxing Train Based on
Overcrowding Control: An Empirical Study from China
Yu Wang *, Xinghua Shan, Hongye Wang, Junfeng Zhang, Xiaoyan Lv and Jinfei Wu

                                          Institute of Computing Technology, China Academy of Railway Sciences Corporation Limited,
                                          Beijing 100081, China; zhangxuegykj@163.com (X.S.); 18810540511@139.com (H.W.); 15210936532@139.com (J.Z.);
                                          hnxxwyk123@163.com (X.L.); 13426481699@139.com (J.W.)
                                          * Correspondence: luoyu167@163.com

                                          Abstract: At the peak of passenger flow, some passengers extend travel sections, which will be
                                          likely to lead to overcrowding of high-speed railway (HSR) trains. Therefore, the problem of train
                                          overcrowding control needs to be considered in ticket allocation. Firstly, by simulating the passenger
                                          demand function and utility function, an optimization model of ticket allocation for multiple trains
                                          and multiple stops with the goal of maximizing revenue is constructed. Secondly, the concepts of the
                                          travel extension coefficient and risk coefficient are introduced, the number of passengers is estimated
                                          under the risk coefficient as the probability, and the total number of passengers on the train arriving
                                          at any station is obtained. Thus, preventing the number of passengers on the train from exceeding
                                          the train capacity is introduced to the ticket allocation optimization model of multiple trains and
                                          multiple stops as a constraint. Finally, this model is solved by the particle swarm optimization
                                          algorithm (PSO). The research results show that the idea of controlling passenger numbers so as
                                          not to exceed train capacity based on ticket allocation proposed in this paper has strong practical
                                          feasibility. By reasonably and accurately allocating the tickets to the departure terminal section and
                                          long-distance terminal sections, it can ensure that, even if there are some passengers extending their
Citation: Wang, Y.; Shan, X.; Wang,       travel section, the train will not be overcrowded under a certain probability, improving the train
H.; Zhang, J.; Lv, X.; Wu, J. Ticket      safety and passenger travel experiences.
Allocation Optimization of Fuxing
Train Based on Overcrowding               Keywords: railway transportation; ticket allocation; train overcrowding control; particle swarm
Control: An Empirical Study from          optimization; sustainable development of railway transportation
China. Sustainability 2022, 14, 7055.
https://doi.org/10.3390/
su14127055

Academic Editor: Luca D’Acierno           1. Introduction

Received: 9 May 2022
                                               High-speed railway is a kind of green, environmentally friendly, and sustainable
Accepted: 6 June 2022
                                          transportation, which is favored by passengers. The factors that impact the sustainability of
Published: 9 June 2022
                                          high-speed railways are mainly economic and safety. High-speed railways can operate well
                                          only by ensuring the revenue of tickets is greater than the cost. Therefore, the goal of ticket
Publisher’s Note: MDPI stays neutral
                                          allocation is to maximize revenue. On the other hand, the safety of HSR trains is important
with regard to jurisdictional claims in
                                          for sustainability as well. However, during the peak period of railway transportation such
published maps and institutional affil-
                                          as holidays, passengers cannot buy tickets for the section they want to take. As a response,
iations.
                                          passengers will purchase any origin–destination (OD) pair ticket from their current station
                                          in order to get on the train first and then buy another continuing OD pair ticket, which
                                          could allow them to extend their travel sections to the target station (terminal station). If
Copyright: © 2022 by the authors.
                                          there are too many passengers extending their travel section (OD pair) in the above manner,
Licensee MDPI, Basel, Switzerland.        the number of passengers on the train will be likely to exceed the train capacity when the
This article is an open access article    train arrives at some stations. This phenomenon is called “overcrowding”, which will
distributed under the terms and           affect the safety of train operation and cause the train to be delayed or even shut down [1].
conditions of the Creative Commons        Therefore, overcrowding especially for the Fuxing train is not conducive to the sustainable
Attribution (CC BY) license (https://     development of high-speed railway (HSR) in China.
creativecommons.org/licenses/by/               When the train experiences “overcrowding”, the conductor should let the passengers
4.0/).                                    who extend their travel section through buying tickets after getting on the train get off;

Sustainability 2022, 14, 7055. https://doi.org/10.3390/su14127055                                     https://www.mdpi.com/journal/sustainability
Sustainability 2022, 14, 7055                                                                                             2 of 12

                                however, the cost is too high in practice, and it is easy to risk negative public opinion.
                                One possible solution to solve the train overcrowding problem is to consider how to avoid
                                train overcrowding when allocating tickets. This means allocating tickets reasonably and
                                accurately under the constraint of controlling passenger numbers so as not to exceed train
                                capacity. Therefore, this paper studies how to avoid train overcrowding through ticket
                                allocation, so as to ensure the safety of train operation.

                                Literature Review and Innovation of This Paper
                                     Ticket allocation of HSR trains is mainly borrowed from the aviation field, because
                                these two fields both take revenue maximization as the objective function. However,
                                there are still many differences between them [2,3]. What is more important is that ticket
                                allocation in HSR is more complex than aviation seat allocation. Thus, according to the
                                difference in complexity and constraints of the application scenarios, ticket allocation in
                                HSR presents a different research focus:
                                (1)   Single-train ticket allocation is the most basic research entry. Ciancimino et al. [4]
                                      first proposed treating different classes of carriages as different train products, so the
                                      problem of train ticket allocation can be transformed into a seat control problem in
                                      single trains, with multiple sections and a single ticket price. Some studies [5] assumed
                                      that the passenger demand obeys an independent normal distribution and used the
                                      particle swarm optimization algorithm (PSO) to solve the final optimization model.
                                      Shan et al. [6] predicted the passenger flow by adopting time series firstly. Then, they
                                      obtained a ticket allocation method through the formulation of rules such as long
                                      distance before short distance, seat before no seat, and allocating tickets in advance
                                      by quantity and then by proportion. Gopalakrishnan et al. [7] mainly considered
                                      the long-distance passenger demand of Indian railways and studied the utilization
                                      method of single-train seat capacity.
                                (2)   Ticket allocation involving multiple trains is further complicated on the basis of single-
                                      train ticket allocation. Jiang et al. [8] integrated the short-term passenger flow demand
                                      forecasting method into the railway multi-train ticket allocation model, which solved
                                      the situation that some stations were short of tickets and other stations were rich in
                                      tickets. Yan et al. [9] developed a seat allocation model for multiple HSR trains with
                                      flexible train formation. Jiang et al. [10] proposed a dynamic adjustment method for
                                      ticket allocation. Zhao et al. [11] proposed a probabilistic nonlinear programming
                                      model for the problem of railway passenger ticket allocation. Deng et al. [12] focused
                                      on the joint pricing and ticket allocation problem for multiple HSR trains with different
                                      stop patterns. Luo et al. [13] developed a multi-train seat inventory control model
                                      based on revenue management theory. The above was discussed with respect to the
                                      complexity of ticket allocation.
                                (3)   Customer choice behavior plays an important role in estimating customer demand,
                                      which has also been more discussed in ticket allocation in recent years. It is an obvious
                                      research conclusion that there are many factors influencing customer choice behavior,
                                      and these factors can be divided mainly into two aspects, personal attributes and trip
                                      attributes, in a great deal of the literature [14–17]. As for the method describing pas-
                                      senger choice behavior, Wang et al. [18] described different passenger needs through
                                      the Logit model and established a multi-stage random ticket allocation model under
                                      passenger selection behavior.
                                (4)   In the two most important sub-studies of revenue management, ticket allocation is
                                      always constrained by ticket prices. However, it is unfortunate that in the past few
                                      years, pricing and ticket allocation issues have always been treated separately, and
                                      there is a gap in the research regarding joint pricing and ticket allocation models [2,19].
                                      Weatherford [20] first stressed the importance of considering prices and suggested
                                      them as decision variables for the ticket allocation problem. After Weatherford’s
                                      contribution, we can see more and more research that has optimized ticket allocation
                                      and ticket prices at the same time. Hetrakul et al. [19] put forward a comprehensive
Sustainability 2022, 14, 7055                                                                                                3 of 12

                                       optimization model of dynamic ticket pricing and ticket allocation based on the impact
                                       of passenger heterogeneity on ticket allocation. Some of the literature regards ticket
                                       allocation as the basis of dynamic pricing and gives priority to solving the problem of
                                       ticket allocation while solving dynamic pricing [21–24].
                                      In summary, we found that there are many scholars who have researched ticket allo-
                                cation based on revenue maximization, but few scholars have studied how to avoid train
                                overcrowding through ticket allocation. As Table 1 shows, the above studies about ticket
                                allocation only take revenue maximization as the objective function of ticket allocation,
                                but lack the consideration of combining the problem of “train overcrowding” with ticket
                                allocation. Therefore, as the most significant innovation, this paper integrates the problem
                                of “train overcrowding” into the ticket allocation model as a constraint. Our research intro-
                                duces a “risk coefficient” as the probability boundary and a “travel extension coefficient”
                                to describe the proportion of passengers who extend their travel section out of the total
                                number of passengers, then constructs and solves the ticket allocation optimization model
                                by taking into account the goal of maximizing the expected revenue of multiple trains
                                and multiple stops under the constraint that the train will not experience “overcrowding”
                                under a certain probability. This is exactly the innovation of this paper and the original
                                intention of writing this paper. It also enriches the research dimension of ticket allocation
                                and sustainable operations and management of railway systems at the same time.

                                Table 1. Comparison of our research with the literature in ticket allocation.

                                                                       Revenue Maximization                       Overcrowding
                                      References
                                                        Single Train      Multiple Trains          Pricing          Control
                                                             √
                                          [4–7]                                   ×
                                                                                  √                   ×                 ×
                                         [8–13]              ×                                        ×
                                                                                                      √                 ×
                                       [2,19–24]             ×                    ×
                                                                                  √                                     ×
                                                                                                                        √
                                      This paper             ×                                        ×

                                     This paper proceeds as follows: Part 2 lists the model assumptions and the variable
                                definition and then constructs a mathematical model formulation; Part 3 provides the
                                algorithms to solve the model; Part 4 shows the numerical experiments; Part 5 concludes
                                the paper.

                                2. Research Methodology and Process
                                2.1. Model Assumptions and Notations
                                      Suppose a high-speed railway line contains l stations and involves K trains, k = 1, 2 . . . K.
                                Each train has different stopping plans and serves the travel demand of a set of OD pairs
                                on the line. Two adjacent stations on the line form a section, named the h section, and in
                                total, h = 1, 2 . . . l − 1.
                                      To simplify the problem, we make the following reasonable assumptions:
                                (1)    Passengers whose requests are fulfilled will not cancel their reservations or change
                                       their ticket.
                                (2)    Take the second-class seat of HSR as the research object.
                                (3)    If passengers need to extend their travel section after getting on the train, they only
                                       make up the tickets to the terminal. The travel section that extends from the boarding
                                       station to the terminal is called the “target travel section (OD pair)”. In order to
                                       get on the train first, passengers buy a short OD pair ticket, and the travel section
                                       corresponding to these tickets is called the “short travel section (OD pair)”. A target
                                       travel section corresponds to several short travel sections.
                                     To simplify the description of the problem, the notations in Table 2 will be used in
                                the formulation.
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                                           Table 2. Notations.

   Symbols                                                                      Definition                                                                               Unit
                                                                         Variable or Parameters
     (r, s)       Origin–destination pair in the transportation service, which is composed of the train stops, from station r to station s                                 /
          t       Station serial number, the train arrives at the tth station                                                                                              /
         h        Section serial number, h = 1, 2 . . . l − 1                                                                                                              /
         k        Train serial number, k = 1, 2 . . . K                                                                                                                    /
         (k)
       prs        Price of train k between (r, s)                                                                                                                         CNY
         (k)
       ηrs        The 0–1 binary parameter denoting whether train k can provide services between (r, s)                                                                    /
         (k)
       trs        Travel time of train k between (r, s)                                                                                                                   min
     α1 , α2      Parameters of utility function                                                                                                                           /
          (k)
     Urs          Total utility of train k for passengers between (r, s)                                                                                                   /
          (k)
      wrs         Probability of train k chosen by passengers between (r, s)                                                                                               %
       Qrs        Expected sales volume between (r, s)                                                                                                                     /
        Ck        Capacity of train k                                                                                                                                  passengers
         (k)
       qt         Total number of passengers on train k arriving at station t                                                                                          passengers
         (k)
       qt·        The number of passengers boarding train k when arriving at station t                                                                                 passengers
         (k)
       q̂t        The number of passengers who get on train k before station t and get off the train after station t                                                   passengers
         (k)
       q·t        For train k, the number of passengers who should get off before station t, but are still on the train after extending their travel section           passengers
        grs       The number of passengers who buy tickets between (r, s), but extend the travel section to the terminal                                               passengers
        β rs      Parameter, travel extension coefficient                                                                                                                  /
         γ        Parameter, risk coefficient                                                                                                                              /
        xrl       Passenger demand under γ for target travel sec tion (r, l )                                                                                              /
    Frl−1 ( x )   Inverse function of cumulative probability function of passenger demand for target travel sec tion (r, l )                                               /
                                                                            Decision Variable
       (k)
      brs                                               The number of tickets allocated to train k between (r, s)                                                          /

                                           2.2. Model Formulation
                                               For any given OD pair, the probability function of passenger demand can be fitted by
                                           normal distribution [25]. Then, passenger demand between (r, s) obeys an independent
                                           normal distribution as follows:
                                                                                                                   ( x − µ )2
                                                                                                exp(− 2σ2rs )
                                                                                                         rs
                                                                                   f rs ( x ) =    √          ,1 ≤ r < s ≤ l                                                        (1)
                                                                                                     2πσrs

                                           µrs is the expectation of passenger demand, while σrs is the standard deviation of passenger
                                                                                                                                                                          (k)
                                           demand. Frs ( x ) is the cumulative probability function of passenger demand. ηrs is the
                                                                                             (k)
                                           service parameter of train k. brs is the number of tickets allocated to train k. If train k
                                                                                                                                      (k)               (k)                 (k)
                                           provides a transportation service between (r, s), ηrs = 1, brs ≥ 0. Otherwise, ηrs = 0,
                                            (k)                  K    (k)    (k)           (k)
                                           brs = 0. Set ∑ ηrs ·brs = Brs . Finally, the expected ticket sales volume between (r, s)
                                                               k =1
                                           can be described as below:
                                                                                                     (k)
                                                                                             Brs
                                                                                             Z                                        Z ∞
                                                                                                                                (k)
                                                                                   Qrs =                   x f rs ( x )dx + Brs ·           (k)
                                                                                                                                                  f rs ( x )dx                      (2)
                                                                                                                                        Brs
                                                                                                 0

                                                When passengers choose a train between (r, s), they will mainly focus on two factors:
                                           ticket price and travel time. The utility obtained by passengers choosing train k can be
                                           expressed as the following formula:

                                                                                                             (k)
                                                                                     (k)                   prs         (k)
                                                                                   Urs = α1                    + α2 · Trs , α1 < 0, α2 < 0                                          (3)
                                                                                                            λ
                                                                                                                                                  (k)            (k)
                                                α1 and α2 are parameters of the utility function. prs and Trs are ticket price and
                                           travel time for train k between (r, s). λ is revised average monthly passenger income [19].
Sustainability 2022, 14, 7055                                                                                                             5 of 12

                                Passengers will choose each train based on utility. Then, we can define the probability of
                                passengers choosing train k between (r, s) by the Logit model as

                                                                                                      (k)               (k)
                                                                                   (k)              ηrs exp(Urs )
                                                                                 wrs =                                                       (4)
                                                                                                  K       (k)             (k)
                                                                                                ∑ ηrs exp(Urs )
                                                                                               k =1

                                     With the goal of maximizing the overall expected revenue, the following objective
                                function is obtained for the ticket allocation of HSR:
                                                                             K
                                                           R = max ∑               ∑ Qrs (brs
                                                                                                      (k)         (k)   (k)
                                                                                                            )·wrs · prs , 1 ≤ r < s ≤ l      (5)
                                                                           k =1 (r,s)

                                        The following constraints shall also be taken into account for ticket allocation:
                                (1)    Train capacity constraints: the ticket number allocated for each train between (r, s)
                                       cannot exceed their capacity constraint. Ck is the capacity of train k

                                                                           h             l
                                                                          ∑           ∑
                                                                                                    (k)
                                                                                                  brs ≤ Ck , h = 1, 2 . . . l − 1            (6)
                                                                          r = 1s = h + 1

                                (2)    Train service constraints:
                                                                               (
                                                                                      (k)                 (k)            (k)
                                                                                   ηrs = 1, brs > 0, brs ∈ Z +
                                                                                    (k)                 (k)                                  (7)
                                                                                   ηrs        =     0, brs      =0

                                2.3. Train Overcrowding Control
                                     In the peak period of the railway, due to the lack of sufficient train capacity, some
                                of the passengers who want to reach the terminal will first buy tickets that can allow
                                them to get on the train from the current station and then make up tickets on the train
                                to extend their travel section to the terminal. Through the above alternative approach,
                                passengers can achieve the goal of getting off at the terminal without buying the target
                                travel section tickets. Although such passengers’ behavior can increase train revenue for
                                railway transport enterprises, it will also bring a problem: overcrowding. This paper
                                estimates the number of passengers on the train when arriving at each station to ensure that
                                the passenger number does not exceed the train capacity for a certain probability. When
                                train k arrives at station t, 1 < t < l, the number of passengers on the train at this time
                                      (k)
                                is qt .
                                                                                   (k)            (k)         _(k)        (k)
                                                                                 qt          = qt· + q t + q·t                               (8)
                                                            (k)
                                        In Formula (8), qt· indicates passengers boarding train k at station t:

                                                                     ∑ min[Qrs ·wrs
                                                           (k)                                    (k)       (k)
                                                           qt· =                                        , brs ], ∀(r, s)|t = r < s ≤ l       (9)
                                                                     (r,s)

                                 (k)
                                q̂t represents the number of passengers who get on train k before station t and get off the
                                train after station t. These passengers are still on the train at this time.

                                                                  ∑ min[Qrs ·wrs
                                                      (k)                                     (k)       (k)
                                                     q̂t    =                                       , brs ], ∀(r, s)|1 ≤ r < t < s ≤ l     (10)
                                                                  (r,s)

                                 (k)
                                q·t means the number of passengers who should have disembarked at station t or before
                                station t, but are still on the train due to the extension of the travel section through buying
Sustainability 2022, 14, 7055                                                                                                         6 of 12

                                a continued OD pair of tickets. This is this segment of passengers that may cause the
                                train overcrowding.

                                                                 ∑ min[ grs ·wrs
                                                       (k)                                     (k)     (k)
                                                      q·t =                                          , brs ], ∀(r, s)|1 ≤ r < s ≤ t    (11)
                                                                 (r,s)

                                                                                           K
                                                                                          ∑ brl
                                                                                                  (k)
                                                          grs = β rs ·( xrl −                              ), ∀(r, s)|1 ≤ r < s ≤ t    (12)
                                                                                          k =1

                                                                           β rl =     ∑ βrs , ∀(r, s) ∈ (r, l )                        (13)
                                                                                     (r,s)

                                                          xrl = Frl−1 (γ), ∀(r, s) 1 ≤ r < s ≤ t, 0 < γ < 1                            (14)

                                     Equation (12) shows that when the passenger demand xrl in the target section (r, l )
                                                                       K      (k)
                                exceeds the supply capacity ∑ brl , the phenomenon of extending the travel section will
                                                                      k =1
                                occur in all short travel sections (r, s). β rs is the travel extension coefficient, which is used
                                to describe the proportion between the passengers extending their travel section and the
                                                            K    (k)
                                excess demand x1l − ∑ brl in the target travel section (r, l ). Equation (14) is used to
                                                          k =1
                                calculate the corresponding number of passengers under the risk coefficient γ. Frl−1 ( x )
                                is the inverse function of the cumulative probability function of passenger demand (the
                                inverse function of the cumulative probability function of the normal distribution in this
                                paper). For the Fuxing train as a representative product of HSR, it is more important to
                                ensure that it is not overcrowded rather than increasing revenue in the actual operation
                                process, which will not affect the train’s operation safety and weaken the passenger riding
                                experience. For a given scheme of ticket allocation, when train k arrives at station t, it needs
                                to satisfy:
                                                                                    (k)
                                                                               qt         ≤ Ck , 1 < ∀t < l                            (15)
                                     Finally, we construct the ticket allocation optimization model of the Fuxing train
                                considering solving the problem of train overcrowding caused by passengers extending
                                their travel sections:
                                                                         K                           (k)      (k)   (k)
                                                     R = max ∑                 ∑ Qrs (brs )·wrs · prs , 1 ≤ r < s ≤ l
                                                                      k = 1 (r,s)
                                                     s.t.
                                                       (k)
                                                     qt      ≤ Ck , 1 < ∀t < l
                                                       h          l                                                                    (16)
                                                                              (k)
                                                       ∑         ∑           brs     ≤ Ck , h = 1, 2 . . . l − 1
                                                     r(= 1 s = h + 1
                                                          (k)        (k)                         (k)
                                                         ηrs = 1, brs               > 0, brs ∈ Z +
                                                          (k)        (k)
                                                         ηrs = 0, brs               =0

                                3. Solution Algorithm
                                     Because the optimization model proposed in this paper is a mixed-integer nonlinear
                                programming model (MINLP) with several constraints (Equation (16)), it cannot calculate
                                the maximum value directly by derivation. Therefore, we chose the heuristic algorithm
                                to solve Model (16). The PSO algorithm is one of the heuristic algorithms that is simple
                                and easy to implement and has fewer parameters, all of which lead to faster convergence
                                speed, and it requires only small computer memory. Moreover, the leap of the PSO
                                algorithm makes it easier to find the global optimal value without being trapped in the
                                local optimal value.
Sustainability 2022, 14, 7055                                                                                                     7 of 12

                                                                                                                          (k)
                                     Setting the initial solution vector A, if train k provides service for ∑ ηrs OD pairs, A is
                                                                                                                  (r,s)
                                      K           (k)
                                the ∑       ∑ ηrs dimension vector. We convert Equation (16) into the following equivalent
                                    k = 1 (r,s)
                                model [2,26]:
                                                                           K           (k)   (k)
                                                                  max ∑            ∑ brs · prs , 1 ≤ r < s ≤ l
                                                                         k = 1 (r,s)
                                                                  s.t.
                                                                  qkt ≤ Ck , 1 < ∀t ≤ l
                                                                    h          l                                                    (17)
                                                                                       (k)
                                                                    ∑      ∑ brs ≤ Ck , h = 1, 2 . . . l − 1
                                                                  r(= 1 s = h + 1
                                                                       (k)        (k)    (k)
                                                                      ηrs = 1, brs > 0, brs ∈ Z +
                                                                         (k)           (k)
                                                                        ηrs = 0, brs = 0
                                                                                                          (k)
                                     Equation (17) is a linear programming model, and brs can be solved directly. Setting
                                          (1)   (1)      (k)
                                A = (b12 , b13 , . . . , brs ), this is the initial solution. Psize is the particle size, and the initial
                                position of the hth particle is recorded as x0h , h = 1, 2, 3 . . . Psize .

                                                                                       x0h = A + gh                                 (18)

                                     In the above formula, gh is a vector with the same dimension of A, and each component
                                obeys the uniform distribution of (−d, d).
                                     xlh is the position at the lth iteration. lmax represents the maximum number of iterations,
                                1 ≤ l ≤ lmax . t(xlh ) can reflect the fitness of xlh , and then:

                                                                                     t(xlh ) = T (Alh )                             (19)

                                Alh is the vector for which each component of xlh is tested by Constraints (6), (7), and (15)
                                and rounded. T (Alh ) represents the output that inputs Alh into the objective function (16).
                                      We set vl+1                                                             l
                                               h as the velocity of the hth particle at the lth iteration. xh is the updated
                                                                                          l
                                position of the hth particle after the lth iteration. yh is described as the best historical
                                position at the lth iteration of the hth particle. ylg represents the historical position of all
                                particles at the lth iteration. The above process can be expressed as follows [19]:

                                                               vl+1   l       l    l    l         l    l    l
                                                                h = δvh + ϕ1 rh1 (yh − xh ) + ϕ2 rh2 (yg − xh )                     (20)

                                                                                    xl+1  l    l+1
                                                                                     h = xh + vh                                    (21)
                                                                  yl+1  l+1          l+1        l+1
                                                                   h = Ah , Th = t (yh ), ∀ t (xh ) ≤ Th                            (22)
                                                        yl+1  l+1         l+1        l+1
                                                         g = Ah , T = t (yg ), ∀ t (xh ) ≤ T, h = 1, 2 . . . Psize                  (23)
                                     Th is the fitness of the best historical position of the hth particle. T is the fitness of the
                                best historical position of all particles. rlh1 and rlh2 have the same dimensions as vector A
                                and obey the uniform distribution of (0, 1). δ, ϕ1 , ϕ2 are control parameters. Finally, the
                                solving process of this paper is as follows (Figure 1).
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                                                                       Begin

                                                       Generate initial solution vector

                                                                 input Psize ,  , 1 ,  2

                                                        Calculate particle fitness

                                                    Initializtion l = 0, h = 1 ,input lmax

                                                  Update particle position by formula(22)(23)

                                                                     x hl +1
                                                              whether satisfied                   N
                                                            constraints(6)(7)(15)

                                                                                Y
                                               Update position of xhl +1 and calculate fitness t ( xhl +1 )

                                                 Update particle position by formula(22)(23)

                                                                                              N
                                                                       h  Psize

                                                                                    Y
                                                                         h = h +1

                                                             N
                                                                       l  lmax

                                                                                Y
                                                                     l = l + 1, h = 1

                                                                        Output A, T

                                                                          End

                                    Figure 1.1.
                                      Figure Solving  process.
                                                Solving process.

                                    4.4.Results
                                         Results  andAnalysis
                                                 and   Analysis
                                      4.1. Basic Data
                                    4.1. Basic Data
                                            We chose the Shanghai–Beijing line in China as an example to verify the validity and
                                          We chose the Shanghai–Beijing line in China as an example to verify the validity and
                                      applicability of the model in this paper. For the situation of multiple trains and multiple
                                    applicability of the model in this paper. For the situation of multiple trains and multiple
                                      stops, there are two trains, G2 and G22, providing service between Shanghai Hongqiao
                                    stops, there are two trains, G2 and G22, providing service between Shanghai Hongqiao
                                      station and Beijing South station. The total second-class seat capacity of each of the trains
                                    station and Beijing South station. The total second-class seat capacity of each of the trains
                                      is set at 1113. Like the Fuxing train, G2 and G22 have few stops and a short travel time
                                    is set at 1113. Like the Fuxing train, G2 and G22 have few stops and a short travel time
                                      (Figure 2), which are deeply favored by passengers. The seat occupation rate of these two
                                    (Figure 2), which are deeply favored by passengers. The seat occupation rate of these two
                                      trains is higher than the average level of all the trains on the same line. During the peak
                                    trains is higher than the average level of all the trains on the same line. During the peak
                                      period of passenger flow, such as holidays, many passengers take these two trains and
                                    period of passenger flow, such as holidays, many passengers take these two trains and
                                      extend their travel section by purchasing continued OD pair tickets, which is likely to
                                    extend   their
                                      increase  thetravel
                                                    risk ofsection by purchasing
                                                            overcrowding.        continued
                                                                           The train          ODtravel
                                                                                      stops and   pair tickets,
                                                                                                       times arewhich
                                                                                                                 shownis likely to 3.
                                                                                                                         in Table
                                    increase the risk of overcrowding. The train stops and travel times are shown in Table 3.
Sustainability 2022, 14, x FOR PEER REVIEW                                                                                                             1

       Sustainability 2022, 14, 7055                                                                                                       9 of 12

                                        “/” means the train does not provide service between the OD pair. There are four st
                                        on“/”
                                            the line,the
                                              means    namely,   Shanghai
                                                         train does          Hongqiao
                                                                    not provide           (SH), the
                                                                                service between  Nanjing  South
                                                                                                    OD pair. There (NS),   Jinan
                                                                                                                    are four       West (JW
                                                                                                                             stations
                                        Beijing  South   (BS).
                                          on the line, namely, Shanghai Hongqiao (SH), Nanjing South (NS), Jinan West (JW), and
                                          Beijing South (BS).
                                                       SH                   NS                         JW                        BS
                                           Departure station                                                                 Terminal

                                           G22

                                           G2

                                                     The train
                                          Figure2.2. The
                                        Figure           trainstop schemes.
                                                                stop schemes.
                                          Table 3. Train stops and travel times.
                                        Table 3. Train stops and travel times.
                                                                                                      OD
            Train          Factors of Passengers Choice
                                                  Factors   of  Passengers                                  OD
                                           Train             (SH, BS)   (SH, NS)    (SH, JW)     (NS, BS)   (NS, JW)    (JW, BS)
                                    Price (CNY)
                                                           Choice
                                                                553
                                                                             (SH,BS)
                                                                          134.5
                                                                                         (SH,NS)
                                                                                      398.5
                                                                                                     (SH,JW)
                                                                                                   443.5
                                                                                                               (NS,BS)
                                                                                                              279
                                                                                                                           (NS,JW) (JW
                                                                                                                          184.5
             G2
                                  Travel time (min)     Price (CNY)
                                                                268        60 553      179 134.5 206 398.5 117443.5        87 279    18
                                            G2
                                    Price (CNY)                 553       134.5         /          443.5       /            /
            G22
                                  Travel time (min)
                                                     Travel time258
                                                                    (min) 60 268 / 60 196 179                  /
                                                                                                                   206      /
                                                                                                                               117
                                                        Price (CNY)             553         134.5         /       443.5         /
                                            G22
                                                     Travel
                                                 We take      time number
                                                         the actual (min) of passengers
                                                                                258 of the60two trains from
                                                                                                          / 30 September
                                                                                                                   196 2019 to/ 7
                                          October 2019 and from 30 September 2020 to 7 October 2020 as a case for empirical analysis.
                                          Then, the estimated values of the main parameters of the passenger demand function are
                                             We take the actual number of passengers of the two trains from 30 Septembe
                                          obtained as in Table 4.
                                        to 7 October 2019 and from 30 September 2020 to 7 October 2020 as a case for emp
                                          Table 4. Main
                                        analysis.       parameter
                                                    Then,         values of passenger
                                                            the estimated      values demand function.
                                                                                        of the  main parameters of the passenger de
                                        function are obtained as in Table 4.                  OD
                                            Parameter
                                                            (SH, BS)     (SH, NS)          (SH, JW)     (NS, BS)      (NS, JW)        (JW, BS)
                                        Table 4. Main parameter values of passenger demand function.
                                                 µrs         1701.4         170              89.6            277          13.4          96.6
                                                 σrs         222.5          92.4             68.7           142.4          14           70.3
                                                                                                         OD
                                           Parameter
                                               The parameter(SH,BS)         (SH,NS)
                                                              value of the utility           (SH,JW)
                                                                                   function is              (NS,BS)
                                                                                               obtained according             (NS,JW)
                                                                                                                    to the literature [25]:          (JW,
                                          α1 = −2.24,
                                                  rs
                                                       α2 = −0.0113,
                                                              1701.4and λ = 190.170 Referring89.6to the finance277
                                                                                                                risk control theory,
                                                                                                                                13.4 the               96
                                          confidence interval of the VaR method is generally 95%, and then, γ = 0.95. The values
                                                              222.5
                                          of otherrsparameters for the example92.4
                                                                                 are as follows:68.7
                                                                                                 P = 25, l 142.4 = 100, δ = 0.5,14 ϕ = 2,             70
                                                                                                       size         max                    1
                                         and ϕ2 = 2.
                                               The parameter
                                             The    behaviors of value
                                                                 extending  travel
                                                                        of the      sections
                                                                                utility      occur inisall
                                                                                          function         the corresponding
                                                                                                         obtained    accordingshort
                                                                                                                                  to travel
                                                                                                                                      the literatur
                                        1 =-2.24 ,  2 =-0.0113 , and  = 190 . Referring to the finance risk control theory, the
                                         sections. It can be seen from Table 2 that both two trains will terminate at BS. For train G2,
                                         the target travel sections are (SH, BS) and (NS, BS). Train G22 only has one target travel
                                        dence  interval
                                         section  (SH, BS).ofTherefore,
                                                              the VaR the
                                                                        method     is generally
                                                                           short travel            95%,NS)
                                                                                          sections (SH,    and   then,
                                                                                                               and       =0.95
                                                                                                                   (SH, JW)       . The
                                                                                                                             belong       values of
                                                                                                                                      to the
                                                                                                  size =25 , lmax = 100 ,  =0.5 , 1 =2 , and  2
                                         target travel for
                                        parameters      section
                                                            the(SH, BS). Similarly,
                                                                example             (NS, BS) hasPonly
                                                                           are as follows:              one short travel section (NS, JW).
                                         All travel extension coefficients of each of the short travel sections are shown in Table 5:
                                              The behaviors of extending travel sections occur in all the corresponding short
                                          Table 5. Travel
                                        sections.   It canextension
                                                            be seen coefficient
                                                                      from Tablevalues.2  that both two trains will terminate at BS. For tra
                                        the target
                                                Arrivetravel   sections
                                                       at the Station  t     are (SH,BS)
                                                                                     NS     and (NS,BS). TrainJWG22 only has one target
                                        section Target
                                                  (SH,BS).
                                                        travel Therefore,
                                                               section         the(SH,
                                                                                    short
                                                                                       BS) travel  sections
                                                                                                 (NS, BS)    (SH,NS)(SH,andBS)(SH,JW) belong
                                        target travel    section    (SH,BS).
                                                 Short travel section           Similarly,
                                                                                  (SH, BS)   (NS,BS)    has
                                                                                                 (NS, JW)   only  one
                                                                                                               (SH, NS)short travel
                                                                                                                              (SH, JW)section (N
                                        All Travel
                                             travel  extension
                                                   extension        coefficients
                                                             coefficient β rs       of each of the0.1short travel
                                                                                    0.065                           sections are
                                                                                                                 0.065             shown in Tab
                                                                                                                                0.035

                                        Table 5. Travel extension coefficient values.

                                                Arrive at the Station t                        NS                                     JW
                                                 Target travel section                       (SH,BS)            (NS,BS)                    (SH,BS)
Sustainability 2022, 14, 7055                                                                                             10 of 12

                                4.2. Computational Results
                                     We used the Python language programming to solve the model. The final ticket
                                allocation details (Scheme I) are shown in Table 6, and the total expected revenue of the two
                                trains is CNY 1,084,120. As can be seen from Table 5, most tickets are allocated to departure
                                terminal section (SH, BS) for both G2 and G22.

                                Table 6. Ticket allocation results (Scheme I).

                                         Train                     OD                  Number of Tickets Finally Allocated
                                          G2                     (SH, BS)                              833
                                          G2                     (SH, NS)                              110
                                          G2                     (SH, JW)                              117
                                          G2                     (NS, BS)                              153
                                          G2                     (NS, JW)                               43
                                          G2                      (JW, BS)                             160
                                          G22                    (SH, BS)                              919
                                          G22                    (SH, NS)                              184
                                          G22                    (NS, BS)                              184

                                     If the aim is not train overcrowding control, just allocating tickets with the goal of
                                maximizing overall revenue (remove Constraints (15)), we can obtain the ticket allocation
                                optimization model under general constraints as a comparison scheme, and the results of
                                the comparison scheme (Scheme II) by solving the model are shown in Table 7.

                                Table 7. Ticket allocation results of comparison scheme (Scheme II).

                                         Train                     OD                  Number of Tickets Finally Allocated
                                          G2                     (SH, BS)                              833
                                          G2                     (SH, NS)                               75
                                          G2                     (SH, JW)                              131
                                          G2                     (NS, BS)                              139
                                          G2                     (NS, JW)                               64
                                          G2                      (JW, BS)                             195
                                          G22                    (SH, BS)                              888
                                          G22                    (SH, NS)                              225
                                          G22                    (NS, BS)                              225

                                     Through the comparative analysis of the ticket allocation results of the two schemes,
                                it can be summarized that, in order to prevent the train from overcrowding, the goal of
                                maximizing the revenue of the trains will be weakened. At the same time, 1752 tickets
                                were allocated for the departure terminal OD pair (SH, BS) in Scheme I, 31 more than
                                the comparison scheme, and more tickets were allocated to the long-distance terminal
                                sections such as (NS, BS) compared with Scheme II. In contrast to long-distance terminal
                                sections, midway short sections such as (NS, JW) or the short departure section (SH, NS)
                                are given more tickets in Scheme II, which will give passengers more opportunities to
                                extend their travel section. It is indicated that, for the sake of controlling the passengers not
                                exceeding the train capacity, the tickets should be given to the departure terminal sections
                                or long-distance terminal sections instead of allocating a large number of tickets to the
                                short sections or short departure sections.

                                5. Conclusions
                                     Different from the general research on ticket allocation, this paper took the risk coeffi-
                                cient as the lower limit of probability and reasonably and scientifically allocated the tickets
                                to each travel section of the train to prevent the number of passengers from exceeding
                                the train capacity resulting from too many passengers extending their travel sections, so
                                as to solve the problem of train overcrowding. After numerical verification, the conclu-
Sustainability 2022, 14, 7055                                                                                                     11 of 12

                                  sions of this paper demonstrated that in the peak period of passenger flow, such as some
                                  holidays, in order to control the number of passengers on the train so as not to exceed
                                  the capacity, railway operation departments should allocate more tickets to the departure
                                  terminal and the long-distance terminal sections, while reducing the number of tickets
                                  for the short-distance or the short departure sections and, finally, achieve a balance be-
                                  tween revenue maximization and passenger riding experiences, which is crucial for the
                                  sustainable development and operation of the HSR [27]
                                        Compared with those ticket allocation literature works that only aim to maximize rev-
                                  enue, this paper provided a new way of thinking about the railway operation department
                                  to reasonably allocate tickets so as to solve the problem of train overcrowding, which is an
                                  innovation for and supplement to ticket allocation theory. At the same time, preventing
                                  train overcrowding can effectively improve the safety of train operation, which is beneficial
                                  to the promotion of passenger experiences. It is of great significance to the management and
                                  operation of railway enterprises and to enhance their market competitiveness. However,
                                  the research conclusions of this paper are based on the assumption that all passengers only
                                  extend their travel to the terminal station and there are no passengers extending travel in
                                  other sections. The situation in real life is obviously more complex than that. In addition,
                                  the optimization model proposed in this paper is a mixed-integer nonlinear programming
                                  model (MINLP) with several constraints. This model is complex and difficult to solve
                                  directly by derivation. We chose the PSO algorithm to solve the model. The iterative
                                  process of the PSO algorithm takes much more time, and there is a small probability of
                                  falling into local optimization.

                                  Author Contributions: Y.W. conceived of this research and completed this paper. X.S. contributed
                                  to all aspects of this work. H.W. conducted an analysis of the case experiment. J.Z. gave critical
                                  comments on the manuscript. X.L. and J.W. collected the data. All authors have read and agreed to
                                  the published version of the manuscript.
                                  Funding: This research was funded by the research plan of China Railway, Grant Number 2021F017.
                                  Conflicts of Interest: The authors declare no conflict of interest.

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