TRANSIMS
Route Planner
The Route Planner module in TRANSIMS produces route plans for every individual according to the activity list generated from Activity Generator. Moreover, the Route Planner also selects the shortest-time path in the network for each individual trip. In addition to the activity list from the Activity Generator, the inputs to the Route Planner module include TRANSIMS network (Transit data and Network data), the vehicle file and the link travel times as feedback from the microsimulator as shown below.
Input/Output flow data of Route Planner module
TRANSIMS assumes that people choose their routes by selecting the shortest time path, given an upper time limit constraint from the activity survey data. TRANSIMS uses a unique algorithm, label-constrained, time-dependent shortest path-finding, in order to select routes for each trip plan of an individual member of a synthetic household.
For example, a trip plan may consist of a trip from home to work, from work to shopping, and then from shopping to home. Each trip plan is a set of trips that represent each individual’s movement between his/her desired activities through the network. Each trip may consist of several legs that are composed of nodes and links which are traversed with a single travel mode. Each leg starts and ends at an activity location, parking location, or transit stop.
A trip from office to home consisting of several legs
In order to find the route for each traveler, the Route Planner transforms the TRANSIMS network to an Internal Planner network for routing purpose. The TRANSIMS network provides information about streets, intersections, signals, parking, activity locations, and transit modes within a road transportation network. Route Planner use this information to construct the Internal Planner Network which consists of nodes, link, travel time on each link, and the possible travel mode on each link. The Route Planner views the network as a set of layers which each belong to each mode as is shown below.
Internal Route Planner network representation
The example below depicts the TRANSIMS network representation of two streets with a bus stop and an activity location on each street. The transit layers can be split into many different transportation layers such as bus route 1 layer, bus route 2 layer, rail 1, etc. The first figure shows a bi-directional street link in the TRANSIMS network between street nodes 1 and 2 and nodes 3 and 4. The second figure- shows the constructed Internal Network for this example.
There are two bus routes connecting the bus stops. Note that each bus stop splits into three nodes. For example, a bus stop BS1 splits into a node for the bus shelter for passengers (S1), a node for the bus-stop place for the bus route 1 (BS1R1), and a node for the bus-parking place for the bus route 2 (BS1R2).
TRANSIMS network representation of two streets with a bus stop and an activity location on each street. There are two bus routes connecting the bus stops.
The Corresponding Internal Network representation
The Corresponding Layers of the Internal Network
There are five different layers in this Internal Network. All activity locations are always placed on the walk layer, while the intersection nodes and parking location are placed on the street layer. The bus layers contain the bus stations, and the two bus route layers. Conceptually, nodes 1, 2, 3, and 4 appear in two different layers, the walk layer and the street layer, even though these appearances correspond to the same nodes in the TRANSIMS network. Generally, each activity location is attached to a corresponding parking location and/or transit stop. Each parking or transit stop must be explicitly connected to appropriate activity locations in the walk-network using process links.
The Route Planner uses trip information to build the network as follows. The first leg of the trip is the walking leg in which the Route Planner searches for possible paths within the walking layer of the network to obtain a walking route from the walking location to the parking location of the individual’s vehicle. When such a path is found, a series of least-cost driving links in the street layer are found to obtain a route to a parking location near his house. A walk route is then developed to move the traveler from the parking lot to his home.
Trips that cannot meet each individual’s goal are fed back to the activity list to choose a new activity time, location or mode for travel to the activity. When all trip plans are done, TRANSIMS passes this information to the Traffic Microsimulator in order to execute these plans.
