We saw the news spread across the headlines of the press: the speed limit to 30 kilometers per hour in Paris would be “The promise of aggravated pollution”, said one. “Cars pollute more at 30 km / h than at 50 km / h in town”, recently had a big daily, before change its title in question. “Speed limit at 30 km / h throughout Paris: pollution risks increasing”, uttered a radio. Will the new measure promoted by the mayor of Paris really increase pollution in the capital? It is more complicated than that, in the opinion of Cerema (Center for Studies and Expertise on Risks, Environment, Mobility and Planning), which produced the study that caused so much ink.
If we stick to the vehicle itself, then yes, explains Benoît Hiron, travel safety manager at Cerema. “A thermal vehicle pollutes more at 30 km / h than at 50 km / h”, in particular because the engines are optimized to run between 50 and 70 km / h. But reducing speed has a whole bunch of impacts that also affect pollution, in particular via the number of vehicles in circulation. “The reduction in the authorized speed allows a better sharing of public space and favors the practice of walking and cycling rather than the use of the car”, explains for example to 20 minutes Laurent Gagnepain, expert engineer in the “transport and mobility” service of Ademe (French Environment and Energy Management Agency).
Caution
A Cerema study carried out in Grenoble showed that the reduction in speed had reduced the number of cars in circulation by 9%, because some motorists switch to other less polluting means of transport, which become more competitive in terms of speed when the maximum speed of the car is lowered. “We finally arrive at a positive assessment” in terms of pollution, according to Benoît Hiron, even if, indeed, driving slower does not in itself reduce pollution.
The Airparif organization, contacted by 20 minutes, is more cautious, and considers that “as it stands, we cannot know if this will have an impact on air pollution”. “The drop in maximum speed can have an impact on the number of cars in circulation (modal shift) and on the flow of traffic. But we can only know these two consequences if we model the impact of this measure on traffic. However the average speed of circulation is already 13 km / h, estimates Antoine Trouche, engineer in charge of the press at Airparif.
An indisputable gain in safety
But lowering the speed has many other impacts, these indisputable and unambiguous, on safety. “The issue of 30 km / h is not on the quality of the air”, explains Tony Renucci, of the association Respire, whose association is nevertheless in favor of lowering the speed of circulation. “Below the optimized speed, the slower the vehicle, the more pollution it emits. (…) But in dense urban areas, in front of schools or homes, security issues are major. As well as noise pollution and the challenges of calming everyday life. And therefore, we are FOR “, writes the association.
A pedestrian accident at 50 km / h multiplies by six the risk of mortality compared to the same accident at 30 km / h, explains Benoît Hiron. This is why, according to this official, 30 zones are developing all over Europe (70% of the urban road in the Nederlands, 100% of single lane streets in Spanish cities, etc.), and that a directive was even adopted in this sense by the European Parliament in 2011. “This is the meaning of history”, insists the researcher, who fears an “instrumentalisation” of data. “When we have a shock on a person, it is neither on the right nor on the left,” said Benoît Hiron, recalling that mayors on the right, like Boris Johnson in London Where Jean-Pierre Gorges in Chartres, implemented a speed reduction.