This research was performed under the Enterprise Program, a FHWA Pooled Fund Study with member agencies from North America and Europe. The main purpose is to use the pooled resources of its members, private sector partners and the United States federal government to develop, evaluate and deploy Intelligent Transportation Systems (ITS). This study explored driver reaction to real-time travel time information posted on roadside dynamic message signs (DMS) in Minneapolis - St. Paul and the Seattle -Tacoma area.
Researchers used an on-line survey to collect data on drivers' opinions relative to diversion route usage when dynamic message signs (DMS) show travel times that are longer than normal. Historical field data (traffic volume data and DMS message records) were also collected to confirm the relationship between increased travel times and use of diversion routes.
In Minnesota, a traveler survey was made available to drivers who visited the MnDOT website. Survey responses were collected between April and September 2012, and a total of 1,030 visitors participated. In Washington, a similar survey was conducted and 693 visitors participated. Researchers noted that the sample sets for each survey were not considered representative of all drivers in each study area.
Field data were also collected to examine how travel time displays impact traffic volumes at four DMS sites in each study area. Traffic volume data were collected from representative sections of the highway having diversion routes downstream from travel time displays. Data were collected for hundreds of days at five minute intervals in each study area. Changes to "thru" traffic were used to estimate diversions based on the following formula: Percent mainline = mainline volume/(mainline volume + exit volume).
Researchers noted that rigorous statistical analysis was not performed. Patterns in the data were used to draw the conclusions below.
Results from the on-line surveys suggested that when posted travel times indicate a trip will take nearly twice as long as the typical travel time for that route, drivers are more willing to take an alternate route.
- In Minnesota, drivers surveyed favored alternate routes when posted travel times were 5-10 minutes longer than typical travel times. In these cases, typical travel times ranged from 5-8 minutes during normal traffic conditions.
- In Washington, drivers surveyed favored alternate routes when posted travel times were 15-20 minutes longer than typical travel times. These types of traffic conditions, however, were rare during the Seattle -Tacoma study. Typical travel times ranged from 15-20 minutes.
- In Minnesota, diversions increased downstream from travel time displays when posted travel times were 5 minutes longer than normal on routes that had normal travel times of 5-8 minutes. Further diversions occurred when travel times increased by 10 minutes more than normal.
- In Washington, diversions increased downstream from travel time displays when posted travel times were 10 minutes longer than normal on routes that had normal travel times of 10-15 minutes. Further diversions occurred when travel times increased by 20 minutes more than normal. In the Seattle study, however, researchers noted that there were few situations where posted travel times greatly exceeded travel times during the data collection period.
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