Traffic forecasting risk: study update 2004.

Traffic forecasting risk research published in 2002 by Standard and Poor suggested that toll road forecasts have generally overestimated traffic by20-30%. A 2004 study update compared toll road forecasting performance for a data set of 87 toll road projects with the predictive record of traffic forecasts made for toll-free facilities. The results supported the earlier conclusion, but showed that toll road traffic forecasts incorporate considerable uncertainty and systematic optimism bias. The results were compared with those of a study by Flyvbjerg, which reviewed the year-one forecasting performance from 183 road projects around the world, of which more than 90% were toll-free. After adjusting for optimism bias, there was little difference between the accuracy of forecasts prepared for toll roads andthose prepared for toll-free roads. For the covering entry of this conference please see ITRD E132365