TruckDistribution

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MTC uses a simple three-step (generation, distribution, and assignment) commercial vehicle model to generate estimates of four types of commercial vehicles. The four vehicle types are very small (two-axle, four-tire), small (two-axle, six-tire), medium (three-axle), and large or combination trucks (four-or-more-axle).

Friction Factors

The trip distribution step uses a standard gravity model with a blended travel time impedance measure. This file sets the friction factors, which are vehicle type specific, using an ASCII fixed format text file with the following data:

• Travel time in minutes (integer, starting in column 1, left justified);
• Friction factors for very small trucks (integer, starting in column 9, left justified);
• Friction factors for small trucks (integer, starting in column 17, left justified);
• Friction factors for medium trucks (integer, starting in column 25, left justified); and,
• Friction factors for large trucks (integer, starting in column 33, left justified).

K-Factors

The trip distribution step also uses a matrix of K-factors to adjust the distribution results to better match observed data. This matrix contains a unit-less adjustment value; the higher the number, the more attractive the production/attraction pair.

-- Main.DavidOry - 27 Jan 2012