Radar-operated speed feedback signs are successful at slowing motorists down along freeway interchange ramps, safety research at Michigan State University has found.
The research — Evaluation of Alternative Messages and Sign Locations on Driver Response to a Dynamic Speed Feedback Sign on a Freeway Interchange Ramp — won national recognition at the 99th annual meeting of the Transportation Research Board, or TRB, in Washington, D.C. this January.
This year’s TRB annual meeting attracted 13,000 transportation professionals from around the world. MSU faculty, staff and students participated in more than 50 presentations, poster displays and workshops.
MSU’s Timothy Gates, Anthony Ingle and Peter Savolainen were awarded the 2020 Best Paper from TRB’s standing committee on traffic control devices.
Gates is an associate professor, Ingle is a teaching specialist and Savolainen is an MSU Foundation Professor and associate chair of graduate students, all in the MSU Department of Civil and Environmental Engineering.
Gates said MSU worked with the Michigan Department of Transportation in 2019 to install radar-operated dynamic speed feedback signs at a freeway ramp curve that had experienced a considerable number of roadside collisions due to drivers traveling too fast into the curve.
“We performed a field evaluation to assess travel speeds and braking behavior in response to three sign messaging alternatives and three sign locations near the curve,” Gates explained. “Depending on vehicle type, the sign reduced speeds upon entry to the curve by 1.0 to 4.0 mph compared to the baseline condition without the sign. They were particularly effective at reducing excessively high speeds prior to entering the curve.”
Savolainen said driver speed selection on ramps is often challenging because the facilities are generally designed in a conservative manner.
“Drivers can often travel safely at speeds significantly above what is advised by signage,” he explained. “However, in cases where dramatic speed reductions are required, drivers do a poor job of adjusting their speeds.”
Savolainen said a good example is the Lansing exit ramp from I-496W to Trowbridge Road, where MSU commuters may notice periodic damage to the roadside barriers and crash cushions due to vehicle strikes.
“This represents a promising solution to actively alert drivers as to unsafe travel speeds at these types of locations,” Savolainen added.
Gates noted that the signs were best at slowing down vehicles that are especially susceptible to rollovers, including heavy trucks and vehicles towing trailers.
“There were only marginal differences in speeds between the three messaging strategies and sign locations, although motorists tended to brake earlier when the sign was positioned further upstream from the curve,” Gates added.