Abstract
The purpose of this report is to address the question whether new or improved roads induce extra traffic. It reviews the direct evidence from both before and after studies of a wide range of schemes, in both Britain and The Netherlands, and from the Department of Transport's monitoring of forecast and observed traffic on 151 trunk road schemes. It investigates whether the induced traffic really matters, and if so, for which type and category of road improvement the increase in traffic is likely to be significant. It also identifies the areas where the current forecasting and appraisal methods should be ammended to allow for induced traffic. Recommendations are made about the method of modifying these.