Considerable public and private resources are devoted to the collection and dissemination of real-time traffic information in the Chicago area. Such information is intended to help drivers make more informed trip decisions, yet its effect on driver behavior remains largely unexplored. This study was conducted to evaluate the effect of traffic reports on route and departure time changes.Downtown Chicago automobile commuters were surveyed during the AM peak period by giving them mail-back questionnaires. Drivers indicated whether or not they had changed their route and departure time decisions based on traffic reports. Further, drivers indicated how they perceived the traffic information system in terms of key attributes. Respondents also evaluated suggested improvements to the traffic information system.A majority (more than 60%) of drivers reported that they used traffic reports for modifying their trip decisions. Drivers perceived radio traffic reports positively in terms of information system attributes. Commuters were more likely to use traffic reports for their route changes if they perceived traffic reports to be accurate and timely, frequently listened to traffic reports, perceived their regular route as congested, knew multiple alternate routes, were male and higher income. Drivers were more likely to change departure times if they perceived traffic reports to be accurate and relevant, frequently listened to traffic reports and perceived their regular route as congested.Drivers indicated a relatively lower level of overall satisfaction with traffic reports indicating the existence of opportunities for improvement. One promising improvement is near-term prediction of traffic conditions on congested and unreliable routes (where conditions may change rapidly). This is because: Drivers generally want to know the conditions at any given point (or link) along their route when they reach that point. Drivers would be able to make better and more informed judgments regarding their trip decisions due to reduced uncertainty of traffic conditions. The possibility that drivers may find traffic conditions significantly better or worse would be reduced. This would improve the credibility of radio traffic reports.