Metaheuristic approaches for urban transit scheduling problem: a review

Urban Transit Network Design Problem (UTNDP) focuses on deriving useful set of routes, manageable timetabling for each transit route and transit scheduling based on available resources. UTNDP is commonly subdivided into Urban Transit Routing Problem (UTRP) and Urban Transit Scheduling Problem (UTSP), respectively. There are various approaches applied to solve the UTSP. The aim of this paper is to give a comprehensive list of studies on UTSP that deals with metaheuristic approaches such as Tabu Search, Simulated Annealing, Genetic Algorithm and their hybrid methods. This review also addressed possible gaps of the approaches and the limitations of the overall problem. It can be concluded that only some of the metaheuristic approaches and sub-problems are highly studied in UTSP. This review will be useful for researchers who are interested in expanding their knowledge and conduct research in UTSP using metaheuristic approaches

Urban transit frequency setting using Multiple Tabu Search with parameter control

Urban transit frequency setting is one of the multiobjective problems in public transportation system, which aims to find optimal time interval between subsequent buses along the routes. In this study, a Multiple Tabu Search (MTS) algorithm is employed to determine the bus frequency of the routes that minimize the number of buses, total waiting times and overcrowding simultaneously. The efficiency of the algorithm is tested on benchmark dataset by changing the value of the total domains. The chosen parameter gives considerable effect on the objective functions compared to other parameters such as the size of tabu list and the number of iterations. Using statistical hypotheses evaluation, the results indicate that the number of domains determines the quality of solutions for different instances of the problem. Additionally, the frequency setting problem is extended by revising the passenger assignment procedure and frequency optimization process with time-dependent demand in order to reflect a real-world scenario. The extended results from different size of routes are presented to show the effectiveness of the proposed algorithm

Frictional behaviour of AA7050/7.5B4Cp/Gr hybrid composites fabricated through stir casting

In this research, AA7050 aluminium alloy strengthened with Boron carbide (B4Cp) and Graphite (Gr) was manufactured by stir casting. The impact of the reinforcing particles on various process parameters on the friction coefficient were thoroughly examined utilizing pin-on-disc apparatus with experiments centred on design of experiments. The outcomes exposed that the coefficient of friction decreases with upsurge in percentage reinforcement and increases with applied load, and sliding distance. With respect to the sliding velocity it decreases until a saddle point, there after it starts to increase. Utilising the response surface methodology, a mathematical model for the friction coefficient was established

Sequential and parallel multiple tabu search algorithm for multiobjective urban transit scheduling problems

Urban Transit Scheduling Problem (UTSP) considers the process of creating timely transit schedules that includes bus and drivers assignment based on the users' and operators’ requirements. This thesis studies multiobjective UTSP consisting of frequency setting, timetabling, simultaneous bus and driver scheduling by applying Multiple Tabu Search (MTS) algorithm. Metaheuristic methods have been widely applied to solve UTSP which is a NP-hard problem. However, there is no applications of MTS in UTSP are known to date. Therefore, MTS is developed from TS with some additional features such as systematic neighbourhood evaluation procedure to reach the near optimal solutions quickly. The ability of MTS approach to exploit and explore the solution space effectively with adaptive memory property makes it more suitable to be used in UTSP. The implementation of MTS begins with the frequency optimization procedure which determines the service frequencies and fleet sizes with the objectives of minimizing the operational cost, passengers’ waiting times at nodes and the overcrowding in the buses. A mixed integer programming models are formulated to represent the objectives. Then, timetabling process is performed to identify a set of departure times at both origin and destination based on predefined parameters. The multiobjective set covering model is used by including some real-world restrictions to find number of buses and drivers as it can represent the problem clearly for implementation. The MTS algorithm is coded in ANSI-C language and tested on benchmark data from Mandl's Swiss Network and Mumford's larger data. Nondominated solutions are produced for every dataset to mark the tradeoff between the conflicting objectives studied in this research. Additionally, the MTS algorithm is also implemented in parallel computing to produce parallel MTS for generating comparable solutions in shorter computational times. The major contribution of this research is to propose MTS method for solving UTSP in both sequential and parallel approach and it is shown that the algorithms are able to produce comparable results for most of the cases from literature and the computational times can be reduced significantly for more than 80% by the parallel execution. As a future work, the research can be extended to find the departure times at every bus stops, provided the number of passengers at each stops

Assessment of mechanical properties of LM13 aluminum alloy hybrid metal matrix composites

Aluminium LM13 alloy based hybrid particulate composites have been processed by adding boron carbide (B _4 C) and titanium diboride (TiB _2 ) particles. The wt% of titanium diboride (TiB _2 ) is varied as 0, 3, 6, 9, 12, 15 and a constant 3 wt% of boron carbide is used to prepare the composites. Stir cast route is used to fabricate the composites. The microstructures of castings are examined using computer aided image analyzer. Vicker hardness, yield strength, ultimate tensile strength and energy absorbed by the composites are examined and reported. The results show that uniform dispersion of TiB _2 and B _4 C reinforcement phases in Al LM13 alloy. Micro hardness of composites enhanced upto 36.6% when compared to Al alloy reinforced with 3 wt% of B _4 C particles. Ultimate tensile strength of Al alloy is improved from 151 MPa to 192 MPa by reinforcing 15 wt% of titanium diboride particles. LM13 aluminium alloy hybrid particulate composites offers superior vicker hardness, yield strength, utlimate tensile strength and impact strength over LM13 aluminium alloy based single particle reinforced composites