By 2020, it is estimated that road accidents will have moved from ninth to third in the worldwide ranking of burden of disease, as assessed in the disability adjusted life years (DALY)^1,2^. Therefore, it is vital to find effective methods to enhance road safety. Speed limits and traffic calming have the potential to reduce injuries due to road accidents^3,4^. Many drivers, however, do not adhere to speed limits^1-7^. Several studies have shown that adherence to speed limits can be explained by the theory of planned behaviour ^5-7^ and that it is possible to focus on drivers&#x27; intentions via self-report questionnaires. It is often difficult, however, to reach the majority of drivers on accident-prone locations with self-report questionnaires. This paper demonstrates an intervention that can be interpreted in the light of two of the theory&#x27;s key variables^8^. It also has the potential to reach a large number of drivers on such locations. It is a speed-displaying device mounted next to the road (especially in villages). It tells drivers their actual speed (which is publicly visible). The measurement takes place continuously, giving the driver the chance to adjust speed and see the new speed shortly thereafter. The results show that the feedback about the current speed is associated with a significant speed reduction relative to a Control condition

Frank Spiegel

Michael Strupp

Rainer Spiegel

Roger Kalla

English

Nature Precedings

1 
<arttitle> Testing a new intervention to enhance road 
safety 
<aug> Rainer Spiegel1, Roger Kalla1, Frank Spiegel2, Michael Strupp1 
<aff> 1Department of Neurology, Ludwig-Maximilians University, Munich, Germany 
2Faculty of Business Sciences, Technische Universität München, Munich, Germany 
<abs> By 2020, it is estimated that road accidents will have moved from ninth to 
third in the worldwide ranking of burden of disease, as assessed in the disability 
adjusted life years (DALY)1, 2. Therefore, it is vital to find effective methods to 
enhance road safety. Speed limits and traffic calming have the potential to reduce 
injuries due to road accidents3,4. Many drivers, however, do not adhere to speed 
limits1-7. Several studies have shown that adherence to speed limits can be 
explained by the theory of planned behaviour5-7 and that it is possible to focus on 
drivers’ intentions via self-report questionnaires. It is often difficult, however, to 
reach the majority of drivers on accident-prone locations with self-report 
questionnaires. This paper demonstrates an intervention that can be interpreted in 
the light of two of the theory’s key variables8. It also has the potential to reach a 
large number of drivers on such locations. It is a speed-displaying device mounted 
next to the road (especially in villages). It tells drivers their actual speed (which is 
publicly visible). The measurement takes place continuously, giving the driver the 
chance to adjust speed and see the new speed shortly thereafter. The results show 
that the feedback about the current speed is associated with a significant speed 
reduction relative to a Control condition. 
 In various areas around Munich (Germany), communities have placed speed-
displaying devices on locations where it is considered particularly important for 
people’s safety that speed-limits are adhered to. Whilst speed cameras have been 
2 
considered effective devices for the prevention of road accidents4, it might be too 
expensive to install a permanent camera at every location where a speed-limit is critical 
(e.g. near every school, playground, elderly home etc.). The cameras need an electricity 
supply and the photos need to be taken and analysed. An alternative way to support the 
adherence to speed limits might be solar-driven speed-displaying devices (mounted next 
to the road), informing drivers and the surrounding public about the driver’s present 
speed. If the speed limit is 50 kilometers per hour and the motorist drives faster (e.g. 63 
km/h), the device displays the 63 kilometers in bright red colour (see Fig. 1a). If the 
driver slows down or speeds up, s/he and the surrounding public can view the new 
average speed shortly thereafter. Speed is displayed until approx. 10 meters before the 
driver reaches the device. If the speed changes towards a speed equal to or slower than 
the speed limit, the colour changes from bright-red to yellow (see Fig. 1a for bright red 
display and Figure 1b for yellow display). 
3 
a 
 
 
 
 
 
 
b 
 
 
 
 
 
 
4 
<LEGEND> Figure 1 The solar-driven device displaying speed in km/h. a, the driver is 
faster than the speed limit of 50 km/h. Hence the speed is displayed in red numbers. b, 
the driver adheres to the speed-limit, so the speed is displayed in yellow numbers. 
 Effective speed management leads to a reduction in road accidents3,4, which 
are on the rise and cause enormous difficulties to both individuals and society1,2. 
According to the disability adjusted life years (DALYs), for example, where one DALY 
represents the loss of one year of equivalent full health9, the consequences of road 
accidents will have moved from ninth to third place in the worldwide burden of disease 
by 20201,2. As speed-displaying devices are specifically made for the purpose to 
enhance road safety, we tested how effective these devices are at reaching a significant 
speed reduction. From a theoretical point of view, there is reason to believe that these 
devices are effective. Although the actual aim of this paper is not to test the Theory of 
Planned Behavior (which is supported by a wide range of studies on human behaviour5-
7, 10-12), nor does literature relate present theories to these devices (a literature search 
including PubMed or PsychIndex did not reveal any literature mentioning or citing 
studies on speed-monitoring devices other than speed cameras), there are at least two 
variables from the Theory of Planned Behavior that would make speed reduction with 
these devices likely: actual behavioural control as well as normative beliefs/subjective 
norm. First, it is likely that these devices enhance control over the driver’s own 
behaviour, because they make it possible to have an eye on the road as well as on the 
device right next to it. Second, normative beliefs referring to behavioural expectations 
(e.g. expectations to avoid putting others or oneself at risk) and the subjective norm 
referring to the perceived social pressure to drive carefully at critical locations (e.g. at 
an entrance to a village) are likely to remind drivers of the need to slow down. 
Perceived social pressure is probably enhanced by the fact that the speed of the driver is 
also visible to pedestrians. 
5 
63 
 This study therefore compared motorists in the presence of the device 
(=Experimental condition) at the entrance to a village with drivers at an equivalent 
location where no such device was mounted (=Control condition). 
<meth1ttl> Methods 
<meth1hd> The devices are mounted next to the road and give feedback about the 
motorist’s average speed, which is assessed via radar (see supplementary material S1 
for further details). The monitoring device used in this experiment displayed the average 
speed from a distance of approx. 55 meters until approx. 10 meters before the device 
was reached, i.e. the first display can show the average speed from Measure Point 1 to 
Measure Point 2 and lies at a distance of approx. 55 meters from the device. The second 
display can show the average speed of the next 45 meters (displayed at a distance of 10 
meters prior to reaching the device), see Fig. 2 for an illustration. 
 
 
100 meters 55 meters 10 meters Device 
Measure Point 1 Measure Point 2 Measure Point 3 
 = Display Point 1 = Display Point 2 
<LEGEND> Figure 2 An illustration of a car driving in the direction of a device, where 
the driver can see the present speed being displayed. The first measurement starts at 
measure point 1 (100 meters from the device). The average speed between 100 meters 
and 55 meters is displayed at measure point 2 (55 meters from the device). The average 
speed between 55 meters and 10 meters is displayed at measure point 3 (10 meters from 
the device). Consequently, the first measurement spans measure points 1 and 2, whilst 
the second measurement spans measure points 2 and 3. In this example, the average 
speed for Display points 1 and 2 are calculated over a distance of 45 meters each. 
6 
<meth1hd> Monitoring was done in kilometres per hour. Speed limits (50km/h) on both 
roads (the one with the device and the one acting as Control condition) were the same. 
For the Control condition, it would clearly have been easiest to measure after removing 
or disabling the device at the original location. This would have been unethical, though, 
as removing or switching off a device which is likely to enhance safety could have 
enhanced risk and would have been unacceptable to the local community. The 
measurement took place during daylight under clear sight, where it is likely to find 
children playing near the road. The study was not immediately carried out after the 
devices were introduced to its present location in March 2006, but 2 years later because 
otherwise it would be hard to say whether they have a stable effect on people’s driving 
behaviour, for drivers may show habituating effects and simply ignore these devices 
after a while. The speed (first measurement vs. second measurement) of 120 motorists 
passing the device (Experimental condition) or 120 motorists passing invisible 
measurement points (Control condition) was measured. In both conditions, it took 
approximately 120 minutes until the vehicles had passed the device (approx. 1 vehicle 
per minute), refer to supplementary material S2 for details about speed assessment in 
both groups. 
 Results In the Experimental condition, the average speed was 50.51 km/h (SE: 
0.42) at the first measurement compared to 48.07 km/h (SE: 0.46) at the second 
measurement. The average speed reduction between the first and the second 
measurement was statistically significant, t(119)=7.06, p<.001. In the Control condition, 
the average speed of the first measurement was 62.13 km/h (SE: 0.69) compared to 
62.04 km/h (SE: 0.7) at the second measurement. For the Control condition, there was 
no statistically significant difference between the two calculated speeds, t(119)=0.36, 
p=.72. Comparing the two conditions at the last measure point 3 (which is the one 
closest to the device in the Experimental condition), there is clear evidence that drivers 
are significantly slower in the presence of the device, F(1, 238)=278.96, p<.001, 
7 
MExperimental condition=48.07 km/h (SEExperimental condition: 0.46) vs. MControl condition=62.04 km/h 
(SEControl condition: 0.7). The results are displayed in Fig. 3. The presence of the device 
also seems to have an effect on how drivers approach the device, because the average 
speed between measure points 1 and 2 is already lower in the Experimental condition 
MExperimental condition=50.51 km/h (SEExperimental condition: 0.42) than in the Control condition 
MControl condition=62.13 km/h (SEControl condition: 0.69), F(1,238)= 207.91, p<.001 (Fig. 3). 
 
0
10
20
30
40
50
60
70
Device No device
1st measurement
2nd measurement
 
<LEGEND> Figure 3 The average speed of 120 motorists each (= 240 cars in total) in 
both Experimental and Control conditions (i.e. in the presence versus absence of the 
speed displaying device). The red line indicates the speed limit of 50 km/h. In the 
presence of the device, drivers reduce their speed to a speed within the limit (difference 
between first and second measurement). When no device was present, there was hardly 
a trend towards speed reduction between the two measurements, which were both 
clearly above limit. 
8 
 Looking at speed changes of individual vehicles, 90 motorists slowed down in the 
presence of the device, 23 kept constant speed, 7 became faster. 60 out of 120 motorists 
were above speed limit at the first display (between measure points 1 and 2), whilst only 
35 were above speed limit at the second display. With no device present (=Control 
condition), 40 motorists slowed down, 39 kept constant speed and 41 became faster. 116 
out of 120 motorists were above limit between measure points 1 and 2 and 116 were 
above speed limit between measure points 2 and 3 (in 114 cases it were the same drivers 
being above limit). 
 
 Discussion In order to have an equivalent comparison between both conditions, 
one could ask for the same average speed to start with (otherwise it is difficult to argue 
that Experimental and Control condition were at comparable locations). This was indeed 
something we considered when carrying out our pilot work. In our 3 pilot experiments 
with 60 motorists per condition (which took place at different locations), the first 
average speed was already significantly higher in the Control condition than in the 
condition where a device had been present. There is at least one reason why the same 
speed cannot be expected. If these devices impact on people, it is likely that they 
approach them with a slower speed in the first place, for drivers might know the 
location of the device already. Consequently, these devices seem to have two effects: 
that people generally drive slower in the presence of them and that they reduce their 
speed. In spite of the fact that these devices do not cause penalty fares, there are several 
ways to explain this behaviour. It can be taken for granted that drivers know about the 
risk of speeding. Likewise, drivers know that other people know that speeding is wrong 
(e.g. pedestrians). One important observation during the study was a group of children 
standing on the sidewalk and yelling at a speeding motorist. Consequently, the 
behaviour of the motorists might be explained by normative beliefs as well as enhanced 
control over their own behaviour. Trying to shift the warning from red letters indicating 
9 
speeding to yellow letters might also have rewarding properties. Taken together, articles 
on road safety have been in the focus of scientific research for more than half a 
century13-19. These results provide a new and alternative way to reach speed reduction. 
 
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<supp> Style tag for supplementary information line ‘Supplementary Information accompanies the 
paper on www.nature.com/nature.’ 
12 
<ack> There are no competing interests. The authors assure that they have no connections to any 
manufacturer or distributor of the devices mentioned in this article. The authors were entirely independent 
in terms of carrying out the study. The authors have received no funding from any manufacturer or 
distributor of speed monitoring devices, nor are they involved doing business with any individual, 
manufacturer or any company that holds business relations with the manufacturers/distributors. The 
authors thank the community of Oberhaching (a local community south of Munich) and the local police 
P31 for permitting them to carry out the study in their community and for their advice in terms of the 
measurement. 
<corr> Correspondence and requests for materials should be addressed to R.S, Dept. of Neurology, 
Klinikum Grosshadern, Ludwig-Maximilian University, D-81377 Munich, Germany, E-mail: 
rainer.spiegel@campus.lmu.de.

Testing a new intervention to enhance road safety

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Testing a new intervention to enhance road safety

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