There has been a growing concern over the past few years both in the United States and abroad over the escalating problem of urban roadway congestion. It is a popular belief that better traffic management, through the application of advanced technologies, can increase the capacity of existing roadways. Numerous demonstration programs are already underway to evaluate the feasibility and effectiveness of various in-vehicle route guidance systems. The objective of this study is to examine the effects of design aspects of in-vehicle route guidance systems when used by a small number of participating vehicles (early stages of development with small market penetration). Such systems are also appropriate for the operation of emergency vehicles, commercial vehicles and other similar service systems. The design parameters of interest are the frequency of information updating, location of information, and level of intelligence. The results from a case study indicate that there are significant trade-offs among the design parameters. Furthermore, benefits to equipped vehicles due to the availability of information on traffic conditions were small with respect to average travel time reductions but significant with respect to improvements in travel time reliability. The results also indicate that improved incident management (if possible) with reduced response times could also be very effective in reducing the effects of accidents, especially when combined with ADIS.