Creating a Route Cost Tables for vehicles in Paramics

'Route Cost Tables' are internal lookup tables that store the travel costs, dictated by the Generalized Cost Equation from each node to each zone depending on the attributes of the vehicle.

The cost tables hold the travel costs for different groups of vehicles (e.g. familiar and unfamiliar drivers) to reach their destination zone i.e. those groups of vehicles effected by the same restrictions in the network (obviously restrictions effect route choice and therefore the cost perceived by a driver).

The values stored in the Route Cost Tables have two basic components these are 'base link costand 'turning delay cost' which is used in the Dynamic Assignment. Base link costs are those costs derived from the length of each link and the link speed of each link and are used to build the cost tables for unfamiliar vehicles. For familiar vehicles the base link costs are supplemented to by the turning delay costs which reflect the delay experienced by vehicle making each turn in the network. The turning delay costs are derived from the congestion in the network and the Dynamic Assignment parameters.

As Familiar vehicles use the base link costs and the turning delay costs when building their route tables their costs from any node to their destination zones can never be less than that for an unfamiliar driver, despite the familiar driver having more knowledge about the network and network conditions.

The category and link cost factors are also considered in the Route Cost Tables as link cost factors are applied in the routing costs for both unfamiliar and familiar Route Cost Tables, while category cost factors are applied to only the unfamiliar Route Cost Tables.

Restrictions can prevent vehicles from using specific links and therefore reduce the routing options available to both unfamiliar and familiar vehicles. This is therefore represented by additional Route Cost Tables that are only available to certain subsets (Vehicle Types) of the vehicle population.

Route Cost Tables are created for a combination of:
1) Familiar and unfamiliar drivers
2) Each restriction type created for the network

A vehicle will only have one Route Cost Table assigned to it depending on whether it is familiar or unfamiliar and any restrictions created that apply to the vehicles vehicle type.

For Example for a network with no restrictions created:
Table 1 - Familiar drivers
Table 2 - Unfamiliar drivers

In a network with two restrictions created:
Table 1 - Familiar drivers no restrictions apply 
Table 2 - Unfamiliar drivers no restrictions apply
Table 3 - Familiar drivers  restriction 1 applies
Table 4 - Unfamiliar drivers  restriction 1 applies
Table 5 - Familiar drivers  restriction 2 applies
Table 6 - Unfamiliar drivers  restriction 2 applies

Base link cost tables can be seen as static tables; as the values held within them will not change once the cost tables have been created when the simulation is loaded/reloaded. The turning delay cost tables can be seen as dynamic tables; as the values held within them may change as the simulation progresses. The turning cost delay Route Cost Tables take into account all the feedback costs gathered as part of the Dynamic Assignment.

Cost perturbation effects are stored at an individual vehicle level and not stored in the cost tables as cost perturbation is a characteristic of the vehicle rather than the network.

Route Cost Tables are rebuilt during every save operation, reload operation, new period and new feedback period. In large networks Route Cost Table can be a considerable size and so take time to build. The size of the route cost tables depends on the number of links/nodes and zones in a network, with two Route Cost Tables create for every Restriction created. In this way minimizing the number of Restrictions create can reduce the number of Route Cost Tables built with every network save, reload or at every feedback period.

'Core Network Attributes > Configuration > Advanced >  Options' has two check box options that can help reduce the time spent reloading Route Cost Tables:
  • Skip route build table during network editing - does not build the Route Cost Tables when a save or reload is applied.
  • Skip route build table on start-up - does not build the Route Cost Tables when the network is initialized or during network editing.
If either option is applied the options must be unchecked to simulate the network. If this is not the case then serious errors may occur.
UPDATED:  October 3, 2019