Errors affecting the different components of traffic predictions.

Errors in assigned traffic volumes are described based on surveys performed in several locations in Europe and North America. Eight methods of expressing the degree of error are identified. Several sources of error are documented including (1) errors affecting estimates of traffic generated by households due to different sample sizes; (2) errors due to sample size in the number of persons trips from a zone; (3) errors affecting traffic between two zones by categories of trips; (4) errors affecting the assignment of traffic to road network; and (5) errors affecting forecasts.