It was a flagship measure of the climate plan of the city of Paris, which is the subject of a standoff with the government: the Paris town hall intends to limit the authorized speed on the ring road to 50 km/h, which , in addition to the creation of a lane reserved for carpooling and public transport, is supposed to “drastically reduce pollution linked to automobile traffic”. But is reducing speed effective in combating air pollution? Is this beneficial in terms of public health, beyond reducing accidents and their severity? Le Figaro takes stock.
All air pollutants affect health, from the respiratory system to the cardiovascular and neurological systems, recalled the environment and energy management agency (Ademe) in a file from November 2023. Fine particle pollution (PM2.5) would be the cause of nearly 40,000 annual deaths (i.e. 7% of total mortality in France), nitrogen dioxide (NO2) 7000 (i.e. 1% of total mortality), possibly we read in a Public Health France report published in 2021. In 2015, the Senate Commission of Inquiry estimated the cost of air pollution at 70 to 100 billion euros per year (including human and natural health). As for the noise generated by traffic, it is also harmful to health. In 2018, the World Health Organization even ranked it among the second cause of environmental morbidity, after air pollution.
Elderly people and children are the most vulnerable, and among the latter those from low-income families in particular, noted a study by the Directorate of Research, Studies, Evaluation and Statistics (Drees) at the beginning of January. However, the poorest households are more likely to live around the ring road, without forgetting all those who benefit from the nearly 300 public places near this road axis, such as parks, stadiums and schools. The city of Paris explains that “lowering the maximum authorized speed will improve the quality of life of the more than 500,000 people living in direct proximity to the ring road, in particular by reducing noise, particularly at night”.
On January 10, 2014, the reduction in the authorized speed on the ring road from 80 to 70 km/h had counter-intuitively led to an increase in average speed of 18%, thanks to the reduction in traffic jams (note that violations linked to speeding increased at the same time). No study directly links this reduction in speed to improved air quality. However, the authorities believe that “it is recognized that the reduction in speed and the flow of traffic have a positive mechanical impact on pollutant emissions”. We can add that accidents on the ring road decreased by 15.5% between 2013 and 2014, when we observed an increase of 5.1% over the same period in Île-de-France.
Concerning noise, the Paris town hall explained that “the reductions in sound levels observed, -1.2 dB(A)* at night, and -0.5 dB(A) during the day, are equivalent to what could be obtained by a reduction of 25% and 10% respectively in traffic volume. The reduction in the speed of the Paris ring road in 2014 therefore had positive effects on congestion, accidents, noise and probably pollution. Will the move to 50 km/h increase these benefits and improve the health of Ile-de-France residents?
In a report published in February 2014, the Environment and Energy Management Agency (Ademe) also specified that “above 70 km/h, speed reductions have a rather positive effect on emissions of particles and nitrogen oxides. Driving slower without traffic jams leads to a reduction in fuel consumption, and therefore pollutant emissions. However, the agency adds that “below 70 km/h, this effect is rather negative”. As for the change from 50 to 30 km/h decided in certain cities, it has not shown any positive trend on this point. Indeed, in urban areas there are numerous slowdown and acceleration zones, and traffic conditions (such as traffic jams) influence fuel consumption and associated pollution. Traffic congestion and the transfer of traffic to other routes are all parameters at the origin of pollution in urban areas; establishing a link between speed limits and a reduction in pollution is therefore complex. Concerning the ring road, some are worried about a transfer of traffic to other axes, in particular on the boulevards of Maréchaux or further outside Paris on the A86.
Road traffic research has shown that the optimal speed of between 50 and 60 km/h reduces the formation of traffic jams when vehicle traffic is at its highest. Researcher Paola Goatin, from INRIA, carried out research on the mathematical modeling of road traffic. His studies enabled the entry into force of a maximum speed modulation system in the Marseille region. The system makes it possible to reduce the maximum traffic speed when traffic becomes denser in order to limit the formation of traffic jams and thus probably limit pollution.
The WHO recommends not exceeding 10 µg/m3 of NO2 in the air, but between 2016 and 2018 the average NO2 content in Paris was 34 µg/m3 while it was almost twice higher, at 65 µg/m3, on roads with traffic such as the ring road. NO2 pollution is therefore particularly problematic in Paris and particularly around the ring road. We note that the majority and main source of NO2 pollution is road traffic. According to a study published by public health France in 2019, an increase of 10 micrograms (µg) of NO2 per cubic meter (m3) leads to a 3.07% increase in non-accidental mortality among people aged 75 and over. the day following exposure. Isabella Annesi-Maesano, professor of environmental epidemiology at Inserm, reports “a 30% increase in asthma for those who live close to a major road. The link between pollution and the development of asthma has been demonstrated and documented.
For her, “it is clear that the passage to 50 km/h on the ring road will reduce the health problems of local residents, especially since it will reduce the levels of ultrafine particles (with diameters less than 0.01 micrometer) emitted by the most recent vehicles and which are the most dangerous for health because once inhaled they pass into the bloodstream. The researcher also highlights the expected benefits thanks to “a reduction in noise, fewer road accidents, less serious accidents, the promotion of active mobility and better health”. However, “the success of this move to 50 km/h will depend on how the population accepts the measure. People need to understand that this is useful.”
*dB(A) is the unit of measurement of sound level (in decibels) taking into account the sensitivity of the human ear to medium frequencies (between 1000 and 4000 hertz).
