Usually it is a combination of several factors that leads to a traffic crash. Below, we will discuss some frequently mentioned causes of motorcycle crashes.
Interaction with other road users
Approximately 50% of all serious and fatal motorcycle crashes in the Netherlands are collisions between a motorcycle and a car and 40% are single vehicle crashes (a crash in which no other road user is involved) [7]. The remaining 10% of the crashes are collisions of a motorcycle with a different road user (cyclist, pedestrian, other motorcyclist, etc).
A large-scale European study (MAIDS) [16] [17] found that crashes involving a motorcycle and a car mostly occur because the motorcycle is not noticed. The MAIDS study made a thorough analysis of more than 900 crashes in five countries (France, Germany, Italy, Spain and the Netherlands) in which a powered two-wheeler was involved. In more than 36% of the cases the driver of the other vehicle had failed to notice the two-wheeler; in 12% of the cases it was the other way round and the rider of the two-wheeler had failed to notice the other vehicle. It must be noted that the data that was used in the MAIDS study (collected in the period 1999-2000) are now obsolete.
More recent crash statistics suggest that motorcyclists are particularly often involved in conflicts with oncoming vehicles that turn off, or with vehicles that entering the main road from a side road onto a main road [18] [19]. These are mainly priority violations committed by a driver [20].
Role of speed
The extent to which speed plays a role in the development and impact of motorcycle crashes in the Netherlands is not precisely known. In theory a higher speed has a negative effect on risk of a crash. A higher travel speed leads to a greater impact in the event of a crash, and, consequently, to more serious injury. At higher travel speeds, there is less time to process information and react accordingly; also the stopping distance is longer. This reduces the possibility to avoid a crash. More information is given in the SWOV Fact sheet Speed and Speed management.
Based on international studies the OECD/ITF working group ' Safety of powered two-wheelers ' concludes, that speed is a bigger factor in motorcycle crashes than in car crashes [9]. Walton & Buchanan [21], for example, found that in New Zealand the speed used by motorcyclists at a T-junction swas about 10% faster than that of the other traffic; and that they violated the speed limit 3.4 times more frequently. In the United States it was found that in 2011 35% of all motorcyclists who were involved in a fatal crash were violating the speed limit at that moment [22]. Drivers were violating the speed limit in 22% of the fatal crashes.
Role of the vehicle (motorcycle as a balance vehicle)
A motorcycle is a balance vehicle, which makes riding it more complex and increases the risk of crashes [23]. 40% of all serious and fatal motorcycle crashes are single vehicle crashes [7]. One of the main causes of single vehicle crashes is that the rider loses control of the vehicle [7]. A technical vehicle problem is rarely the cause of a crash [24].
Infrastructure and condition of the road surface
Infrastructural factors such as a cluttered or unclear design, improper use of materials and poor road maintenance play a demonstrable role in 8% of the motorcycle crashes [24]. For several reasons road features can present problems for motorcyclists, especially in combination with humidity. Speed humps, markings, grates and drain covers may cause problems as they get slippery in damp weather or create differences in level on the road, which affects stability. Furthermore, sand on the road is more dangerous for a two-wheeler than for a car [24].
Role of (types of) guard rails
A guard rail is designed to prevent vehicles from entering a danger zone next to the roadway. For cars, but also for motorcycles, these are very effective in the prevention of head-on collisions with objects or road users travelling in the opposite direction. However, for motorcyclists guard rails themselves can also be a risk. If a motorcyclist hits an (unprotected) guard rail in a crash, it can lead to serious injuries [24]. Crashes with guard rails and other road screenings play a role in 2-4% of the fatal motorcycle crashes in Europe [9].
In General, each unprotected obstacle is a danger for motorcyclists, even if they are classified as 'crash friendly' for car drivers (light poles, shrubs, small trees, road signs). Motorcyclists find ‘Cable barriers’ the most dangerous roadway separations [25], but research found no difference in crash severity between ‘cable barriers’ and other guard rails [26].
