Traffic simulation

Discrete event simulation models are both stochastic (with random components) and dynamic (time is a variable).

Employing a numerical method with a car-following model (such as Gipps' with Heun's) can generate important information for traffic conditions, such as system delays and identification of bottlenecks.

The methods noted above are generally used to model the behavior of an existing system, and are often focused around specific areas of interest under a range of conditions (such as a change in layout, lane closures, and different levels of traffic flow).

Transport planning and forecasting can be used to develop a wider understanding of traffic demands over a broad geographic area, and predicting future traffic levels at different links (sections) in the network, incorporating different growth scenarios, with feedback loops to incorporate the effect of congestion on the distribution of trips.

On the other hand, modeling of transportation system operations and design focus on a smaller scale, such as a highway corridor and pinch-points.

Lane types, signal timing and other traffic related questions are investigated to improve local system effectiveness and efficiency.

Modeling railways for freight movement is important to determine the operational efficiency and rationalize planning decisions.

With new advancements in mathematics, engineering and computing, simulation software programs are increasingly becoming faster, more powerful, more detail oriented and more realistic.

Microsimulation relies on random numbers to generate vehicles, select routing decisions, and determine behavior.

Because of this variation, it is necessary to run the model several times with different random number seeds to obtain the desired accuracy.

Microsimulation models usually produce two types of results: animated displays, and numerical output in text files.

It is important to understand how the software has accumulated and summarized the numerical results to prevent incorrect interpretation.

MOEs are the system performance statistics that categorize the degree to which a particular alternative meets the project objectives.

For example, most HCM procedures assume that the operation of one intersection will not be affected by the conditions of an adjacent roadway (with the exception of HCS 2000 Freeways).

In order to use microsimulation outputs to find LOS, the delay must be accumulated over 15 minute intervals and averaged over several runs with different random seeds.

(If this is the case, a work-around can be to temporarily ignore those effects and extend the network or storage area for the link to include the maximum queue length.