The Washington State Department of Transportation has produced this guide to improve the development of traffic forecasts used by Department engineers and planners. The guide is intended to help standardize the methodology for developing forecasts, provide an “audit trail” of the steps and assumptions behind each forecast, and ensure that the assumptions underlying the forecasting process have been carefully considered.
This guide is split into two volumes. The first volume describes the forecasting process and reviews the issues that must be addressed. The second volume provides more detailed instructions for the forecasting process. Volume 2 assumes that the user is already familiar with the issues that affect traffic forecasts and understands why different inputs to the forecasting process are important. Persons new to traffic forecasting should read Volume 1 before continuing with this volume.
Volume 2 of the guide describes the steps required to perform a forecast for WSDOT. The guide assists planners in obtaining and organizing the information needed for a forecast, provides guidance on the factors to include in a forecast, and gives a consistent structure for analyzing those data and reporting results.
The appendices provide an extra set of worksheets and tables for the forecasting process, directions for using the Lotus spreadsheet templates that are discussed in Chapter 3, summary information on four-step computer models supported by WSDOT, a summary of data sources for the forecasting process, an example forecast, and a set of 3-1/2 inch IBM PC compatible diskettes that contain the Lotus 1-2-3 templates discussed above.