Transit Assignment

This page provides an overview of the transit modes and skimming and assignment procedures. For more information on the inputs, outputs, and parameters of the transit models, please see the Transit Inputs and Transit Assignment Results pages.

Local vs. No Local Transit Mode Determination

The transit mode number determines if a transit mode is included in the "NoLoc" alternative paths and potentially enables a discount to the in-vehicle travel time (IVT) and additional time bonus to represent the enhanced reliability, station amenities, ride quality, information, etc. that is associated with non-local services.

The following table lists the available mode numbers. Note that mode number 31 is the only local service.

The second table below defines the IVT discount and bonus associated with each mode number.

Note that the base travel time discounted is the sum of the dwell time and travel time on the highway network links. Unless the highway network link has a transit speed set, the congested time is used. Dwell time is set in the Inputs\Transit\TSPEED.DBF and defined by the USERA4 transit line attribute (see table below).

Transfer and Boarding Penalties

In the transit path builder, transfer and boarding penalties are uniform across all modes, except between Tri-Rail (mode 11) and I-95 Express Buses (mode 15) and between express buses, which have a high penalty to discourage transfers.

In mode choice, a fixed 1 minute per transfer penalty is applied to walk and KnR access alternatives. A 10 minute per transfer penalty is applied to PnR access alternatives.

Transfer and Boarding Penalties are defined in the transit factor files (Inputs\Transit\TFAC_XXX.FAC).

Transit Access Points

Transit paths are built between Transit Access Points (TAPs), which function as pseudo-TAZs to leverage Cube's Public Transport program to build the paths and assign trips.

The connections between each MAZ and each TAP within walking distance is found and measured over the all-streets network.

The drive access distance to each TAP that allows parking is measured from the trip origin TAZ to the TAZ in which the TAP is located. TAP parking availability and service range are defined in the highway node attributes.

Finally, the ultimate (and best) Origin MAZ – Boarding TAP – Alighting TAP – Destination MAZ path for each line-haul mode is computed by the Virtual Path Builder within CT-RAMP.

Not all transit stops are designated as TAPs, instead the following criteria is used to:

• All stops coded on Commuter Rail routes are identified as TAPs
• All stops coded on Urban Rail and Light rail routes are identified as TAPs
• All stops coded on People Movers and Circulators are identified as TAPs
• All stops coded on Express Bus and BRT routes are identified as TAPs
• First and last stop on Local Bus routes are identified as TAPs. Additional stops located at approximately 0.5 mile intervals are identified as TAPs. Stops that are used by multiple routes are also identified as TAPs.

Transit Time-of-Day

There are three transit time-periods: AM Peak, PM Peak, and Off Peak (representing midday and evening / overnight service)

Transit Modes Supported

SERPM 8 Transit is segmented according to access mode, egress mode, and mix of transit modes used.

• The mix of transit modes are segmented by whether a local service is used at all (WithLoc) or if only non-local services are used (NoLoc). Non-local services are defined as rail and modes with exclusive right of way. In the mode table below, Regional/Inter-County Services and Premium modes are all considered non-local.
• Supported access modes are Park-and-Ride (PnR), Kiss-and-Ride (KnR), and walk.
• Supported egress modes are walk or auto. Auto egress is only available when no local transit service is used in the path.

These segments define 9 transit modes:

• Walk_WithLoc_Walk
• Walk_NoLoc_Walk
• Walk_NoLoc_Auto
• PNR_WithLoc_Walk
• PNR_NoLoc_Walk
• PNR_NoLoc_Auto
• KNR_WithLoc_Walk
• KNR_NoLoc_Walk
• KNR_NoLoc_Auto

Note that these modes are relative to the tour production end. For example, a PNR_NoLoc_Walk trip on the return half-tour would have the auto leg of the trip on the egress (home) end. SERPM 8 produces a trip table for each transit mode by time of day.

Skimming and Assignment

Transit skims are rebuilt within each speed feedback iteration because the transit travel times are updated each iteration based on the highway congestion. Transit assignment is conducted in an origin-destination format and is completed after the speed feedback has converged. Transit assignment is not capacity constrained, thus the trip loading does not impact level-of-service conditions.

Skimming and assignment are done for each of the 9 transit modes listed above. Transit paths are built sensitive to the weighted in-vehicle and out-of-vehicle time, number of transfers, and transit fare. The results are aggregated in the transit ridership summaries (Transit Boarding Statistics*.xlsx; Transit Trip Summaries*.xlsx saved in the _reports folder).

The weighted in-vehicle time and other time discounts applied to premium transit modes are described in Transit Inputs.