City of Greater Sudbury Transportation Study Report

For all other trips (i.e. external trips either traveling through Greater Sudbury or having an
origin or destination outside Greater Sudbury) a base year p.m. peak hour external trip table
was developed using the household survey records, the external trip table from the 1992
Transportation Study, traffic counts, and a procedure in TransCAD which generates trip
tables based on partial survey information and traffic counts.
Although there are several methods for performing trip distribution, a gravity model was
deemed the most appropriate method for the Greater Sudbury model for internal trips. The
determination of the number of trips between traffic zones becomes a function of the number
of trip productions at the origin zone, the number of trip attractions at the destination, and
some function of travel between the zones, which in the case of Greater Sudbury is travel
time. The general form of the gravity model is shown in the following equations:
Tij = Ai* Bj* Oi* Dj* Fij
Where Tij= Trip interchanges between origin zone I and destination zone j,
Oi= Total trip productions at origin zone I
Dj= Total trip attractions at destination zone j,
f(t(ij))= Travel deterrence function, in the case of Sudbury it is an inverse
exponential function of time defined as;
f(t(ij))= e -ßt(ij)
Where ß= a calibration parameter,
t(ij)= auto travel time from zone i to zone j
A,B = balancing factors
With this form of the gravity model, as travel time between zones increases, the number of
trips between those traffic zones decreases.
Typically, home based work (HBW) trips have different trip making characteristics than home
based other trips and non home based trips and for this reason it was decided to calibrate
two gravity models for internal trips. This means that a ß parameter needs to be calibrated
for HBW trips and another for all other trips (i.e. home based other and non-home based
trips).
The TransCAD software has a built-in routine for calibrating gravity models and this was
used to determine the parameters to be used in the gravity models. A p.m. peak hour
travel time matrix, and p.m. peak hour trip observed tables for both purposes are required to
perform this task. These calibrated parameters are as follows:
Home Based Work - ß = 0.0370
All Other trips - ß = 0.0412
CITY OF GREATER SUDBURY
OFFICIAL PLAN BACKGROUND REPORT
September 2005 Page 47