The frequency of speed limit violations
Observed speed limit violations
Speed limit violations are very common. Typically 40% to 60% of the drivers exceed the limit. Typically, around 10 to 20% exceed the speed limit by more than 10 km/h (OECD, forthcoming). The amount of violations on an individual road depends on many different, local aspects, including
- The local speed limit
- Characteristics of the road and road environment
- Traffic density and traffic composition
- The level of enforcement
- The country.
Drivers may intentionally or unintentionally exceed the speed limit, since speed choice and motives for speeding are affected by many factors.
Monitoring vehicle speeds nationally
To assess the extent of speeding violation nationally, countries should carry out speed surveys annually on a representative sample of their roads with different speed limits. Speed survey sites should be at locations where drivers can choose “free-speeds”, if they are not likely to be restricted by congestion or by local speed reducing measures.
The British Department for Transport carries out annual surveys at 27 sites on motorways, 7 sites on dual carriageways, 26 sites on rural single carriageway A class roads, and 36 sites in urban areas. Speed distributions are reported for up to ten different classes of vehicles.
The Dutch Ministry of Transport reports average speeds, percentage violations and the V90 per month, based on continuous measurements at 40 locations at motorways (100 or 120 km/h limit). A distinction is made between three vehicle types by their length. Only speeds in conditions where cars can drive faster than 75 km/h are included in the monthly average. Various regional and local road authorities collect speed data for their roads. However, there is no uniform, national processing of this data.
Self reported speeding behaviour
The SARTRE 3 survey provides information on self reported speeding behaviour for different road types. Most self-reported speed violations occur on motorways; least self reported speed violations occur in built-up areas. The percentage car drivers that report to violate the speed limit often, very often or always on different road types are
- Motorways: 24%
- Main roads between towns: 18%
- Country roads: 12%
- Built-up areas: 8%
The percentage of self reported speed violators is considerably smaller than the observed percentages. In assessing self-reported behaviour and when developing speed campaigns, it is important to recognize that the reasons for socially unacceptable behaviour such as speeding are often understated in relation to the reporting driver and overstated for other drivers . Another reason could be that a few kilometres faster than the speed limit is not considered a speed limit violation by the drivers themselves.