Use in-vehicle audible alerts in addition to visual safety alerts to improve speed limit compliance.
A 500-participant Minnesota Road Fee Test Study investigated technologies to charge mileage-based user fees and improve compliance with traffic control devices.
Made Public Date


United States

Connected Vehicles for Safety, Mobility, and User Fees: Evaluation of the Minnesota Road Fee Test


In 2007, the Minnesota Legislature appropriated $5,000,000 for a technology research project exploring mileage-based user fees (MBUF). The Minnesota DOT (Mn/DOT) was tasked with leading the effort of executing a pilot project to demonstrate technologies that would allow for the eventual replacement of the gas tax with a cost-neutral mileage charge.

The objective of the Minnesota Road Fee Test (MRFT) was to inform future public policy decisions regarding mileage-based user fees and connected vehicle applications. To accomplish this, Mn/DOT utilized a commercially available after-market device and a smartphone to assess mileage-based user fees.

Lessons Learned


The in-vehicle safety alerts used two different kinds of alerts: visual and audible. Visual alerts showed the same traffic control device on the smartphone as appeared on the roadside (e.g., curve signage). Audible alerts worked by making the smartphone beep when the vehicle was traveling more than 5 mph over the posted speed limit for the area (e.g., school zones, speed zones). In this study there were a total of 98 signage zones, including school zones, speed zones, curves, and construction zones. Participants in the overall MBUF study were surveyed and interviewed regarding their experience with the visual and audible alert functions of the study smartphone device.

Lessons Learned

Use in-vehicle audible alerts in addition to visual safety alerts to improve speed limit compliance and reduce speeds on hazardous roadways. Both visual and audible alerts appear to have improved speed limit compliance and reduced driver speeds, though drivers showed a greater reduction in speed when presented with audible alerts. Nearly all respondents who saw the visual safety alerts reported they somewhat agreed or agreed that they knew why the alerts were displayed (97%), the alerts were easy to read (98%), and the alerts were easy to understand (99%). Most respondents also somewhat agreed or agreed that they understood why the audible safety alerts occurred and that the audible safety alerts were easy to hear, with 95% of the experienced respondents responding this way to both statements.