This report discusses the effectiveness of using variable message signs (VMS) and in-vehicle traffic advisory systems (IVU) on a mountainous pass (Snoqualmie Pass on Interstate 90 in Washington state) for changing driver behavior. As part of this project, variable message and variable speed limit information were placed along a 61-km segment of I-90 between North Bend, Washington, and Cle Elum, Washington, where I-90 passes over the Cascade mountains through Snoqualmie Pass. The signs, which were implemented during the winter of 1997-98, provided weather and roadway information to motorists with the intention of reducing the number and severity of accidents.
An analysis of accidents on Snoqualmie Pass was conducted with historical accident data. Several accident models were used to estimate accident frequencies and severity. The report reviews the analysis of speed data over Snoqualmie Pass and reports on lane-mean speeds and deviations.
Next, the potential users' needs for variable message information and their willingness to use in-vehicle information were assessed. A survey was distributed and analyzed to explore these questions. An econometric analysis was performed of potential speed reductions for various weather conditions. A second set of analyses was then performed on the surveys to investigate the characteristics associated with drivers who would use an in-vehicle system and those who would not use the information provided by the in-vehicle unit.
A laboratory experiment was conducted on the use of an in-vehicle system and VMS. A driving simulator was used for this study. Mean speed and deviation from the mean speed were analyzed, as was the effectiveness of the systems over each 4.68-km (3-mile) stretch. The effect of VMS on the relationship between mean speeds and speed deviations was analyzed.