Three associations, including the Drivers’ Defense League, conducted an experiment to demonstrate the harm caused by certain speed bumps, which they consider illegal, in terms of consumption, but especially CO 2 emissions .

Thursday, July 1 , the Drivers’ Defense League published an unprecedented study on the nuisances linked to speed bumps , and in particular those built, according to it, ” non-standard “, which are sprouting up almost everywhere in the territory in recent years. In partnership with the association For Serene and Sustainable Mobility (PUMSD), the “Automobile club of lawyers ” and experts from Automobile magazine, the experiment aims to prove that some of these obstacles, designed to limit speed on certain sensitive roads, cause numerous inconveniences, even dangers, inside and outside the vehicle.

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The associations make a first observation: in addition to the “ speed bump ” or trapezoidal type speed bumps which are the norm in France, “ plateau ” or “ cushion ” type speed bumps are multiplying in the territory and cause numerous noise nuisances, discomfort, excess fuel consumption, but also excessive CO 2 emissions . Today, the regulation of “ speed bumps ” and trapezoidals is governed by a decree dating from May 27, 1994. According to this text, speed bumps must be located in the 30 km/h zone, have a platform of between 2.5 and 4 meters, with two slopes 1 to 1.4 meters long and must not exceed 10 centimeters high. However, the “ trays ” and “ cushions ” are sometimes much higher and longer.

The measurements of “speed bumps” or trapezoidal speed bumps, according to the 1994 decree. L’Automobile magazine

A life-size experience

Last May, the three associations therefore had two speed bumps built on the private roads of a construction company in Marcoussis (Essonne). One with dimensions deemed to comply with the decree, the other with a height of 24 centimeters, well above the recommended 10. Two test vehicles, representative of the French automobile fleet, were used for the experiment: a Renault Clio and a Peugeot 3008. Under the supervision of a bailiff, consumption was calculated using flow meters, comfort with an accelerometer positioned under the driver’s buttocks and the noise emitted using a sound level meter, positioned seven meters from the car’s path.

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The results of this experiment are clear: the legal retarder increases fuel consumption by 10.5% for the Clio and 13% for the Peugeot, while the retarder deemed illegal increases it to 26 and 28% respectively. For the Clio, CO 2 emissions go from 183g of CO 2 /km without a retarder, to 202g for the legal retarder (205 for the Peugeot) and 230g (232 for the Peugeot) for the retarder deemed illegal for the Clio. “ These installations are counterproductive in terms of pollution ,” comments the spokesperson for the Drivers’ Defense League, Alexandra Legendre, for Le Figaro . Nuisances “ all the less acceptable as manufacturers and drivers are under enormous pressure to reduce them as much as possible ”, she adds.

The consequences of speed bumps on CO 2 emissions . Drivers Defense League

Concerning comfort, the study also points to a real physical shock for the passengers of the two cars. If the Clio like the Peugeot clears the legal speed bump quite easily, the speed bump deemed illegal causes two big bounces when going uphill, due to contact with the suspension stops and another when going down. Significant shocks which reverberate on the back despite the very reduced pace, notes the study. Finally, noise pollution is also increased by the speed bump deemed illegal: firstly because of the sharp deceleration, up to 15 km/h, necessary to pass the obstacle, but also from the frequent scraping of the front and rear bumpers of the two cars.

Confused legislation?

The League for the Defense of Drivers does not, however, question the usefulness of speed bumps, but their number (more than 450,000 throughout the country), and the supposed illegality of some. Longer and higher, they would escape regulation, because the Center for Studies and Expertise on Risks, Environment, Mobility and Development (Cerema) “ no longer considers them as trapezoidal type speed bumps “, says Alexandra Legendre. Concretely, the association deplores that Cerema’s recommendations distinguish between trapezoidal type retarder (concerned by the decree) and ” plateau ” type retarder, implying that the flat part of the equipment, from the moment it measures more than four meters long and is no longer trapezoidal.