Simulation Modeling

Abstract

Simulation is generally defined as an imitation of a system or process, while computer simulation is the replication of a system or a process on a computer. Simulation has been used in many fields in order to understand interactions between system components or evaluate alternative designs. It is routinely used in various and very diverse environments, including the training of pilots using flight simulators, in weather prediction, in the design of communications networks, as well as in entertainment (e.g., video games).

In transportation, simulation is used to study various aspects of the system, including port, airport, and rail operations, demand modeling, interactions between land use and transportation, and traffic operations. The use of computer simulation models has become particularly prevalent among transportation practitioners and researchers. Such models typically replicate the movement of units of traffic (automobiles, buses, pedestrians, etc.) along a simulated network, considering the interactions between the environment, the vehicle, and the driver. Simulation can be very helpful in evaluating alternative solutions for transportation systems where analytical techniques cannot be applied or are not available, and it can consider the effects of microscopic characteristics such as individual driver behavior and vehicle characteristics.

Problems

• 1. Identify and briefly describe a specific traffic operational problem in your area. For example, consider overflowing left/right turning bays, spillback from a downstream signal to an upstream intersection, and other such congestion-related problems. Provide the exact location, along with a sketch of the pertinent geometric characteristics of the area. Would you recommend the use of simulation for studying this problem and recommending alternative solutions?

• 2. Conduct a literature review and identify three different applications of traffic simulation programs. For each of them describe the model type, the model capabilities, and any shortcomings identified during the model application. Briefly describe the application of the model and the results obtained.

• 3. Develop a GPSS simulation program to replicate the operations of an all-way stop-controlled intersection with the following characteristics:

  • NB approach: Demand = 160 veh/h, 10 % left, 80 % through, 10 % right

  • SB approach: Demand = 300 veh/h, 5 % left, 80 % through, 15 % right

  • EB approach: Demand = 280 veh/h, 10 % left, 40 % through, 50 % right

  • WB approach: Demand = 330 veh/h, 40 % left, 40 % through, 20 % right

  All approaches have one lane per direction. What is the average queue, the maximum queue, and the average delay per approach?

• 4. There is an entrance to a parking lot along a two-lane, two-directional highway. The driveway has a queuing capacity of two vehicles, in addition to the ticket pickup spot (see sketch below).

  

• 5. Vehicles arrive during the peak hour (8–9 a.m.) from the eastbound direction at a rate of 280 veh/h (arrivals are Poisson distributed). Of these, 40 % enter the parking lot. During the same time, the arrival rate from the westbound direction is 250 veh/h (Poisson distributed). Of these 15 % enter the parking lot. Each driver can pick up their ticket within 30–60 s, uniformly distributed. Model the entire system in GPSS, and provide:

  • (a) A flowchart of the simulation model. Clearly state any assumptions you need to make.

  • (b) The GPSS program that describes it.

  • (c) Run the program 15 times and provide a summary of the average queue lengths for each direction, and the average time it takes for each vehicle to travel through the system.

  • (d) Determine when and where there are queues developing. Do you have any suggestions for improving the system?