Report numberRA-MOW-2011-033
TitleHomogenisation of speeds
AuthorsJohan De Mol
Dirk Lauwers
Koen De Baets
Georges Allaert
Published byPolicy Research Centre for Mobility and Public Works, track Traffic Safety 2007-2011
Number of pages88
Document languageDutch
Partner(s)Universiteit Gent
Work packageOther: Sustainable transportation

The aim of this research is to investigate whether the database “Road signs” could be used to homogenise speed regimes. It also examines what the effects of homogenised speed zones could be on the number of road signs.
Driving speed is an important factor in road safety. Speed not only affects the severity of a crash, but is also related to the risk of being involved in a crash. T


he speed is not only a quality criterion within a transport system but should also take into account the need for structural safety margins.


A human as the vulnerable road user is the weakest element in the road traffic system. This vulnerability explains the injury in an accident. The vulnerability is in relationship with the purely biomechanical properties of the human being, the speed-related released kinetic energy in a collision and the characteristics of the vehicle. The number of accidents depends heavily of the varying conditions in traffic and environment.


Flanders, with its fragmented space and his historically not very well planned underlying road network, is characterised by strong changes in road structure and environment. Most research reports conclude that speed differences at road section level (larger speed variance) is related to higher crash rate.


However, - taking into account these varying characteristics - the number of changes of the speed limit on a road has to be kept as limited as possible.. Changes in the speed limit and differences of speed in the traffic flow and speed differences between different vehicles increase the risk of accidents. Larger differences in speed between vehicles are related to a higher crash rate. Without exception, a vehicle that moved (much) faster than other traffic around it, could have a higher crash rate.


There is also – mainly because of the limitations of the capacity of the road user –a need to simplify the traffic tasks. Homogeneity in the traffic flows is needed. If this is translated to the characteristics of the vehicle, the mass and speed of the vehicle along with the directions in which the traffic participants move, determine the degree of homogeneity. Through greater homogeneity, one can reduce the possibility of conflict: how more homogeneous the traffic is, how limited the chances of a conflict/accident.


After outlining the legal framework, the theoretical framework -within the categorisation of roads and within the possible environmental factors- that may determine the speed regimes, is situated.


In Belgium apart from vehicle related speed, the road administrator makes specific speed regulations related to the categorisation of the road. Whether the existing general maximum speed (90 km/h) should be changed in to lower general speed level (70 km/h) should be framed within the safety goals and within driving comfort and an acceptable traffic flow. To achieve these goals a homogenizing of the speed regimes could be a solution.


In seven cases (chosen within a spatial framework), the effect of lowering the overall speed of 90 to 70 km/h is examined. Here the length of the road segments where the maximum speed changes and the chosen speed within a specific road categorisation is described. Although the application of these generic scenarios (more effect of the application of the zone boards can be expected) on the database (road signs) are only a first analysis, the result on the number of speed signs, is important.


The conclusion is that reducing the speed from 90 to 70 km/h, 6 on 7 speed signs can be removed. Less speed signs reduce the needed attention and the workload for the driver; more smoother and safer traffic could be the result.

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The Policy Research Centre for Traffic Safety carries out policy relevant scientific research under the authority of the Flemish Government. The Centre is the result of a

cooperation between Hasselt University, KU Leuven and VITO, the Flemish Institute for Technological Research.


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