Evaluation of Dynamic Speed Display Signs (DSDS)

There is considerable interest in new technology that has the potential for reducing speed and improving traffic safety. One technology that seems to offer this potential is Dynamic Speed Display Signs (DSDS). DSDS detect and display approaching driver’s their current speed. A new version of DSDS does not display the current speed to drivers, but a feedback message whether or not the driver complies with the actual speed limit. The basic idea is not only warning drivers exceeding the speed limit but also rewarding them for speed compliance. The German Insurers Accident Research Department conducted a series of field studies evaluating the effectiveness of this type of Dynamic Speed Display Signs (DSDS).

Dialog-Displays wirken besser als Geschwindingkeitsanzeigen

Methods and procedure

The DSDS consists of a solar power supply, a radar device and the actual display sign. The upper half of the sign displays permanently a picture illustrating the reason for speed reduction, e.g. children. The lower part of the sign displays feedback about keeping the speed limit to approaching vehicles. A green “Thank you” message is displayed to vehicles driving at or below the speed limit. A red “SLOW” message is displayed to vehicles driving above the speed limit. LED pixels outline the characters and provide visibility also at night. No message is displayed if no vehicle is detected or the DSDS is switched off.

The DSDS were installed at four different test sites in Berlin. All sites are urban roads with one lane per direction. The sites differ in traffic and pedestrian volume, speed limit and visibility condition. One DSDS for each direction was provided.

The data was collected during three study periods for each test site:

  • before the DSDS was switched on (4 weeks),
  • while the DSDS was in operation (3 to 9 months), and
  • after the DSDS was switched off (2 to 6 months).

The radar device at the DSDS collected continuously data about date and time, speeds and sizes of passing vehicles. At selected sites there was an on-street survey of pedestrians about their safety perception.

Results

In general the results of the field studies indicate that the Dynamic Speed Display Signs have a significant and ongoing effect on vehicle speed and speed variance. The main results are:

  • The average speed decreased by 1.8 to 4.2 km/h.
  • The 85th percentage speed decreased by 2 to 6 km/h.
  • The percentage of drivers exceeding the speed limit decreased by 42% to 64%.
  • Pedestrians reported less critical incidents while crossing the street and lower vehicle speed.

These effects were maintained over the entire operation period of the DSDS. After switching the DSDS off speed parameters returned to its baseline.

Recommendations

Based on the results of these field studies the German Insurers Accident Research Department recommends Dynamic Speed Display Signs for supporting overall traffic calming in sensitive urban areas such as school zones, residential areas or pedestrian crossings. If DSDS are installed they should be in operation permanently. The German Insurers Accident Research Department does not recommend Dynamic Speed Display Signs for mitigating traffic accident hot spots.

Reduktion der Geschwindigkeit im Vergleich