Dynamic speed displays are large digital sign-boards that broadcast your speed as you travel past. Although they admonish you to slow down if you exceed the speed limit, do they provide effective feedback that changes driver behaviour and reduces risk of accidents, injuries and fatalities? What can we learn from dynamic speed displays that may help in changing other health-related behaviours?
The speed limit on a high traffic road near where I work is 60 km/hr. Yet, unless it’s raining or foggy, the average speed is likely 80 km/hr or more (based on my own observations of what speed I need to travel at to match the speed of other vehicles). Recently, a new pullout and dynamic speed display were installed on the the side of the road and traffic police routinely set-up here to monitor speeds and ticket offenders. I was curious to learn more about the effectiveness of these devices, as not only am I interested in the feedback mechanisms, but this is a road I cross on my daily commute (either walking or cycling).
A 2003 study conducted by the Texas Transportation Institute investigated the effectiveness of dynamic speed displays on reducing speeding (1). Do the signs reduce driver speed? Is the reduction in speed maintained further down the road? If the signs are permanent, do drivers still slow down months after the signs were installed? The researchers selected several driving scenarios to investigate, including school zones (both at the upstream transition as well as the school zone itself), speed limit changes upstream of signalized intersections on highspeed roads and upstream of sharp curves in the road. Prior to installing dynamic speed display signs at test locations, baseline measurements of traffic speed were recorded at each site. Traffic speed was then measured at 1 week after the signs were installed and again 4 months later. Driver speeds were assessed both upstream of the display as well as at the display in order to determine the change in speed.
What did they find? One beneficial observation was a reduction in the average speed in school zones of 9 mph after installation of dynamic speeds displays. Additionally, this slower average speed was still maintained 4 months later. However, at other locations, the display had less of an effect. For example, dynamic displays installed upstream of sharp bends in the road did not lead to signification reductions in speed. Why are the dynamic speed displays more effective in school zones? Evidence from other disciplines suggests the possibility that we put the safety of others above our own. Youth are more likely to be responsive to quitting smoking if they know of the health risks of second-hand smoke to others than health risks to themselves (2); perhaps greater concern for the safety of school children triggers increased responsiveness to displays in school zones.
This suggests that the variability in the effectiveness of the signs may be linked to specific conditions at the different locations. For example, other traffic warnings at sharp curves in the road (recommended speed signs, warning chevrons, etc..) might already provide drivers with sufficient information to slow down through the corner. Alternatively, the added information from the dynamic speed display may be lost amonst the other messages to change speed or direction. Dynamic speed displays were also found to be more effective in locations where speeding is enforced more frequently.
In British Columbia, there is also evidence to support the effectiveness of dynamic speed displays in reducing the average speed of traffic. A sign installed on the Trans Canada Highway south of Nanaimo led to a reduction in average speed of 6 km/hr and that over 50% of drivers were travelling at speed less than the posted speed limit (3). These results are helpful to transportation ministries who are faced with the challenge of selecting strategies that encourage drivers to slow down; knowing the types of locations where dynamic speed displays are most likely to reduce driver speed helps ensure cost-effective deployment.
A fun alternative tactic (though perhaps less practical) that combines feedback with rewards might offer even more success in encouraging drivers to obey speed limits. The Fun Theory (an initiative by Volkswagen) hosts a competition to recognize thoughts, ideas or inventions that help change behaviour by promoting fun. The recent award winner was the Speed Camera Lottery – instead of simply ticketing violators, Kevin Richardson, winner of the award, proposed that those who obey the speed limit are entered into a lottery to win money (collected from the fines on those who were caught speeding). Would the incentive of potentially winning money be enough to encourage you to slow down?
Most of us are guilty of speeding, whether its enjoying the thrill along a fast stretch of highway with no one in sight, or zipping more quickly than we should through a school zone. Yet most Canadians also recognize the inherent dangers of speeding – increased risk of collision, injury and death (4). Understanding the conditions that make feedback effective at eliciting behaviour change may provide opportunities to transfer the lessons learned in traffic control to other complex problems.
1. Ullman, G., & Rose, E. (2005). Evaluation of Dynamic Speed Display Signs Transportation Research Record, 1918 (1), 92-97 DOI: 10.3141/1918-12
2. Glantz SA, Jamieson P. (2000) Attitudes toward secondhand smoke, smoking, and quitting among young people. Pediatrics. 106(6): E82 PMID: 11099625
3. Cst. Tim Schewe (Ret.) Are Speed Reader Displays Effective? DriveSmartBC. April 2011.
4. Transport Canada (2005) Driver Attitude to Speeding and Speed Management: A Quantitative and Qualitative Study – Final Report. EKOS Research Associates Inc. http://www.tc.gc.ca/eng/roadsafety/tp-tp14756-menu-398.htm TP14756 E