Dynamic Speed Feedback Signs

Dynamic speed feedback sign (DSFS) systems are traffic control devices that are programmed to provide a message to drivers exceeding a certain speed threshold.

A DSFS system typically consists of a speed-measuring device such as a loop detector, radar, or message sign, which displays feedback to drivers who exceed a predetermined speed threshold. The feedback may be the driver's actual speed, a message such as SLOW DOWN, or activation of a warning device (such as beacons or a curve warning sign).

A study by Hallmark et al. (2015) evaluated the effectiveness of two different types of DSFS systems in reducing speed and crashes on rural two-lane curves in seven states (including Iowa).

One sign displayed a regular speed feedback sign when drivers exceed the posted or advisory speed and the other displayed the corresponding speed advisory sign when the driver exceeded the posted or advisory speed. Signs were installed at 22 curves on rural two-lane roads in each of the seven states.

Large reductions in mean and 85th percentile speeds were noted at most sites. Significant reductions were also found in the fraction of vehicles traveling over the posted or advisory speed limit.

The researchers also compared crashes before and after installation of the signs using around three years of before data and two years of after data. Control sites were also included in the analysis. Results are shown here:

Crash Type CMF
all crashes 0.95
all in the direction of the sign 0.93
all SV crashes 0.95
SV in the direction of the sign 0.95

More information is provided in these tech briefs:


Hallmark, Shauna, Neal Hawkins, and Omar Smadi. Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project. Federal Highway Administration, 2015.

Image: A dynamic speed feedback sign system with a speed-measuring device

A DSFS system with a speed-measuring device (Shauna Hallmark et al./Institute for Transportation)

Image: Speed display sign on a rural curve

A speed display sign used in the seven-state study (Shauna Hallmark et al./Institute for Transportation)

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