Speed choice: why do drivers exceed the speed limit?
A large majority of the drivers consider speed as a very important problem for road safety. More than 80% of the European drivers state that driving too fast is often, very often or always a contributory factor in road accidents . At the same time, many drivers exceed the posted speed limits. Sometimes this may be intentionally, sometimes it is unintentionally. Speed choice is affected by characteristics of the driver, by factors related to human perceptual skills and limitations, by characteristics of the road and the road environment, and by characteristics of the vehicle.
Speed choice and driver characteristics
Many drivers prefer to drive faster than the objective risk justifies, but also than what they themselves consider to be a safe speed. Motives for exceeding the speed limit are both rational and emotional and may depend on the temporary state of the driver or the actual situation. There are also more permanent personality characteristics that affect speed choice and explain differences between individual drivers and groups of drivers. These types of driver characteristics are related to speed preferences and speed violations.
People generally prefer to drive faster than is safe
Drivers, who prefer higher speeds, also consider higher speeds to be safe. In addition, almost all drivers want to drive faster than the speed that they themselves consider to be a safe speed . According to the SARTRE 3 survey , around 20% of the European drivers report driving a little faster or much faster than other drivers. At the same time, only around 5% state that they drive more dangerously than other drivers. Apparently, dangerous driving is not related to speed in the mind of most of these drivers.
What are drivers' motives for exceeding the speed limit?
Most drivers openly admit that they more or less regularly exceed the speed limit. They provide the following reasons for these intentional speed limit violations  (They adapted their speed to that of the general traffic stream
- They were in a hurry
- They generally enjoy driving fast
- They were bored
The arguments are both rational and emotional. Enjoying driving fast is a very common argument. According to the SARTRE 3 survey almost 10% of the European drivers agreed that they very much enjoy driving fast.
Another reason for exceeding the speed limit is that the driver is unaware of the speed limit. It may be assumed that this is an unintentional violation. Either a speed limit sign was absent or the driver missed it; in both cases the road characteristics are insufficiently informative about the speed limit in force.
Not all drivers are the same
Not all drivers choose the same speed. First of all, there are differences between individual drivers. These individual differences may have to do with personality characteristics. For example, a clear relationship has been established between preferring to drive fast and a general preference for risky, sensational and challenging activities .
Secondly, it is possible to distinguish different groups in relation to speed preferences. For example, it has often been found  that
- Young drivers prefer to drive faster than elderly drivers;
- Male drivers prefer to drive faster than female drivers;
- Drivers driving for professional purposes prefer to drive faster than drivers driving for private purposes.
Perceptual skills: underestimation of driving speed
All motor vehicles have a speedometer to check the driving speed objectively. Nevertheless many drivers seem to rely as well on their subjective perception or 'feeling' of their speed when it comes to speed choice . However, human perceptual skills (and limitations) affect the subjective experience of speed and may lead to overestimation or underestimation of the driving speed. Hence, the subjective perception of speed is not very reliable. From a safety point of view, underestimation is the most dangerous.
Three types of situations easily lead to underestimation of one's own driving speed  :
- Situations in which a high speed has been maintained for a long period, for example on long-distance trips on motorways. In these cases, the travel speed will increasingly be underestimated, resulting in higher speeds without the driver noticing.
- 'Transition' situations, where drivers must reduce their speed significantly after a period of driving at a high speed. When entering the lower speed zone, drivers will underestimate their travel speed. This is, for example, the case when leaving the motorway and entering a lower speed zone and when entering a village from a major through road. It may also be the case when a long straight section of road is followed by one or more curves.
- Situations where there is little peripheral visual information. For example, wide roads without points of reference, driving at night or in fog provide little peripheral information and are likely to lead to underestimation of the driving speed.
Speed choice and the road/vehicle characteristics
The road environment may also elicit speed limit violations. There are large differences in the amount of speeding between individual roads of the same category and with the same speed limit. Incompatibility between the posted speed limit and the (implicit) message of the road and the road environment may be the reason. The road is insufficiently 'self-explanatory'. Either intentionally or unintentionally an imbalance between speed limit and the road characteristics may cause drivers to exceed the speed limit.
The characteristics of the car fleet continue to develop, particularly for cars. Some of these characteristics may affect speed choice:
- Engine power increases: cars can be driven faster;
- Comfort increases: there is less discomfort at high speed;
- Landrover-type cars increase: SUVs (Sport Utility Vehicles) and other 'land rover' type of cars become increasingly popular. This type of cars has high wheels, distorting the perception of speed. Speed will be underestimated.