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TRANSIMS
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TRANSIMS FUNDAMENTALS

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ADDITIONAL TRANSIMS INFORMATION

TRANSIMS

Traffic Microsimulator

The Traffic Microsimulator module in TRANSIMS executes travel plans and computes the overall intra- and inter-modal transportation system dynamics. The Traffic Microsimulator is updated every second to ensure that dynamic vehicle behaviors are captured with enough fidelity to generate realistic overall traffic behavior. Interactions of travelers produce emergent traffic behaviors, such as congestion, which consequently are used to compute vehicle emissions. The input and output data flow of the microsimulation is shown in the figure below.

TInput/Output flow data of Traffic Microsimulator module; The inputs to the Traffic Microsimulator module consist of TRANSIMS network, vehicle file, and traveler plans obtained from the Route Planner, There are three major types of output from the Traffic Microsimulator: Traveler Event Output Data - which report almost everything that happens to a traveler, Summary Data - which consists of spatial and temporal data. Spatial summaries include data aggregated over user-defined sections of roadway along the street networks, for example, densities and total flow in a 150-meter section. Temporal summaries include data about travel times along streets at various times of day and Snapshot Files - Traffic animation can be produced from the snapshot files, which contain time, position, and velocity information for each vehicle in the simulation.
Input/Output flow data of Traffic Microsimulator module

The input to the Traffic Microsimulator module consists of TRANSIMS network, vehicle file, and traveler plans obtained from the Route Planner. Each individual moves from one activity to another according to the plan obtained from the Route Planner, using combinations of modes such as walking, driving or riding in a vehicle. All vehicle movements are simulated in detail to include driving on roads, stopping for signals, accelerating, decelerating, changing lanes, stopping to pick up passengers, etc.

Vehicles follow a set of rules that guarantee that no vehicle collisions will occur. This movement is accomplished by using a cellular automata principle. Each section of roadway is divided into cells as shown in the figure below.

Cellular Automaton Microsimulation
Cellular Automaton Microsimulation

Each cell either contains a vehicle or is empty. This simulation is carried out in discrete timesteps. For each second, the vehicle decides whether to accelerate, brake, or change lanes in response to the nearby vehicles in the grid. The simulation guarantees that each vehicle makes decisions based on the state of every other vehicle in its surrounding at the same time.

There are three major types of output from the Traffic Microsimulator:

Traveler Event Output Data — which report almost everything that happens to a traveler.

Summary Data — which consists of spatial and temporal data. Spatial summaries include data aggregated over user-defined sections of roadway along the street networks, for example, densities and total flow in a 150-meter section. Temporal summaries include data about travel times along streets at various times of day.

Snapshot Files — Traffic animation can be produced from the snapshot files, which contain time, position, and velocity information for each vehicle in the simulation.