Over a quarter of (registered) road deaths in the Netherlands are due to run-off-road crashes (see the question How often do run-off-road crashes occur?). It can be deduced from crash registration BRON that half of the run-off-road crashes involve a crash with a tree. Trees within the clear zone are therefore considered road safety hazards.
A recurrent misconception is that trees close to the road reduce speed and could therefore benefit road safety . However, crash research on roads with a speed limit of 80 km/h and higher (in the Netherlands and abroad) shows that obstacles close to the road, including trees, increase the risk of a serious crash by about a factor of one and a half to two . This implies that (unshielded) trees within the clear zone, regardless of a possible limited restraining effect on driven speeds, significantly increase the risk of a serious run-off-road crash.