City of Greater Sudbury Transportation Study Report

4. TRAFFIC FORECASTING MODEL
4.1. Model Overview and Model Limitations
Greater Sudbury’s traffic forecasting model is comprised of four stages, which include Trip
Generation, Trip Distribution, Mode Split and Assignment as shown in Figure 4.1.1. The
components of the model are further explained in the following sections. Trip generation
equations were developed to determine the number of trips generated by each traffic zone
and the number of trips attracted to each traffic zone. The trip generation equations are
based on the findings of the household survey. Trips have been categorized into three trip
purposes; home-based work, home-based other and non-home based. Trip distribution
involves the determination of the destination choices of trip makers (i.e. determines the flow
of trips between traffic zones) using the productions and attractions determined from the trip
generation model. A gravity model was used to distribute internal trips (trips having an origin
and destination inside of Greater Sudbury) and the furness bi-proportional method for
external trips (i.e. trips traveling through
Greater Sudbury or having an origin or
destination outside of Greater Sudbury).
For many municipalities in Canada, this
is the preferred method of performing
trip distribution.
Land Use Data
Figure 4.1.1 - Model
Trip Generation
Work, Home-Based Other,
Non-Home Based
External Trips
For the assignment of trips to the
network, the equilibrium assignment
technique within TransCAD was used.
TransCAD is a travel demand modeling
software that can be used to predict
changes in travel patterns due to
changes in development, demographics,
and transportation choices. This is
discussed further in the next section.
Since the gravity model requires travel
times, which reflect delays caused by
traffic, the model is run iteratively
between the gravity model and trip
assignment.
Road Network
Road Network
Travel Times
Apply Factors
Peak Hour, Occupancy,
Mode Split
Trip Distribution
Work, All Other and Non-
Home Based Combined
Auto Assignment
Apply Growth Rates
The model was validated at the screenline level and is capable of producing reasonable
forecasts at the screenline level and at the link level. Link level forecasts were compared to
recent traffic counts to ensure accuracy. However, forecasts from this model cannot
accurately simulate turning movements at intersections, as this model does not take into
account driver behavior, delays at intersections and opposing traffic. For intersection turning
movements, the validated link flows could be used as input into traffic simulation software
that can be used to estimate turning movements.
CITY OF GREATER SUDBURY
OFFICIAL PLAN BACKGROUND REPORT
September 2005 Page 38