What is the real impact of illegal speed bumps?

Our colleagues from Automobile Magazine studied the true cost of illegal speed bumps, based on several criteria.

You have all come across at least one of them. And for good reason, according to a study conducted by Auto Plus in 2018, no less than 40% of the 450,000 speed bumps on our roads are illegal, due to their excessive height. If the standards vary according to the type of infrastructure – Berlin cushion or speed bumps – they must in any case not exceed 10 centimeters in height. However, many of them do not take this regulation into account, causing many inconveniences for motorists. More pronounced braking, jerking, risk of damaging the shields, among others. If many associations are campaigning to remove all illegal speed bumps, they dragged on and things are actually progressing relatively little. However, the installation of this type of device has many consequences, which we wanted to study our colleagues fromAutomobile Magazine. The result is an exciting study on the impact and the true cost of illegal speed bumps, with results obtained through life-size tests, using a legal speed hump and a second of 24 centimeters, thus exceeding the regulatory size.

Noises, jolts, fuel consumption, everything has been analyzed, under the supervision of a bailiff. And the least we can say is that the results are nothing short of edifying. Two vehicles were used: one Peugeot 3008 PureTech 130 EAT8 and a Renault Clio TCe 100 X-Tronic, passing the legal retarder at 25 km / h and the second at 15 km / h. The opportunity to demonstrate the negative effects of this type of infrastructure, both on fuel consumption and on occupant comfort. To study this point, the journalists who carried out this investigation placed sensors under the driver’s buttocks, responsible for measuring the force of the tremors. If these do not exceed 0.3 g on the legal retarder passed to 25 km / h, they then reach 0.4 (ascent) and 0.5 g (descent) on the illegal speed bump, despite a speed of 15 km / h. Not to mention the aftershocks, enough to give the occupants a hell of a backache, not to mention the impact on the vehicle’s suspensions!

Consumption and noise pollution

But passenger comfort and the deterioration of the car’s condition are not the only concerns highlighted by this study. Unsurprisingly, our colleagues also noted an increase in noise pollution caused by illegal speed bumps. To do this, they simply placed a sound level meter 7 meters from the backs of donkeys and compared the measurements. If the noise is barely louder on the legal retarder compared to normal traffic, passing an illegal installation at 15 km / h emits 2 to 3 dBA more. It is even worse if you set the retarder to 18 km / h, when the noise level can be up to eight times higher. A difference which is explained, among other things, by the greater re-acceleration due to the height of the device, not to mention the noise caused by the suspensions and the possible friction of the sills. Moreover, our colleagues emphasize that “ these values would be even higher with trucks, tractors, trailers ».

Finally, and this is arguably the most obvious point: illegal speed bumps dramatically increase fuel consumption. As the Automobile Magazine specifies, the passage of a legal speed bump leads to an increase of between 10 and 15%, against 26 to 28% for an illegal device. A big difference which can be explained again by the fact that the greater height leads to stronger braking and therefore greater acceleration. For example, the Renault Clio displays an average consumption of 7.94 l / 100 km-, which drops to 8.77 l on a legal retarder and 10 l on an illegal blackcurrant.