Speed Bumps May Induce Improper Drivers’ Behavior: Case Study in Italy

Many studies conducted over the last 20 years show that speed bumps have only a limited affect in decreasing traffic speed, especially compared to better designed passive speed control devices, such as speed humps or cushions. These findings were confirmed during an investigation described in the present study conducted in an Italian town. Besides the well known phenomena, such as sudden slow down and acceleration before and after the bump (which is often a source of accidents), it was observed that drivers tend to perform all sorts of maneuvers to reduce their discomfort as much as possible when approaching the undulation. This fact is particularly evident on streets where the speed bumps do not extend over the entire street. This kind of misplacement seems to encourage drivers to perform avoidance maneuvers, such as short deviations into the opposite lanes or parking lanes and bus stops. This study is an attempt to reach a qualitative and quantitative classification of possible alterations in drivers’ behavior due to the presence of the speed bumps. The result of more than 25,000 observations of cars and motorcycles reveal that speed bumps, where not properly installed, induce many drivers (up to 50% for cars and up to 85% for motorcyclists) to avoid the undulation to reduce the level of noise and vibrations perceived inside/on the vehicle.