Less cars in central Paris, more pollution on the outskirts

Traf­fic con­ges­tion in urban areas is noth­ing new. The city of Paris, known for its traf­fic jams, tried to improve urban flow by increas­ing the num­ber of lanes in the 1980s. But this attempt led to what is known as the Bræss para­dox. That is, adding or mod­i­fy­ing roads (and thus the num­ber of lanes) mod­i­fies the flow of traf­fic to the point that it actu­al­ly reduces over­all effi­cien­cy instead of reduc­ing con­ges­tion. In addi­tion, the prob­lem of con­ges­tion is also close­ly linked to the issue of pol­lu­tion, in par­tic­u­lar air pol­lu­tion. Accord­ing to the WHO, air pol­lu­tion is respon­si­ble for 4.2 mil­lion pre­ma­ture deaths per year world­wide¹, caused in par­tic­u­lar by expo­sure to (ultra)fine par­ti­cles in cities. In response to this grow­ing pub­lic health cri­sis, sev­er­al lane clo­sure poli­cies have been intro­duced, although they are reg­u­lar­ly chal­lenged due to the lack of evi­dence regard­ing their sup­posed effect on air quality.

In 2016, the City of Paris closed a cen­tral road that runs along the riv­er, known as the “voie Georges-Pom­pi­dou” or “les voies sur Berges”. Used by around 40,000 vehi­cles per day over a dis­tance of 3.3 km, this stretch of road pro­vid­ed access to Paris and cer­tain sub­urbs for com­muters. While the clo­sure of this thor­ough­fare has had a num­ber of ben­e­fi­cial effects with­in the city – such as air qual­i­ty, need for more pub­lic space, and reduc­tion in noise pol­lu­tion – com­muters have tend­ed to divert jour­neys to oth­er routes rather than take pub­lic trans­port. As a result, the west to east-bound lanes of the south­ern ring road (“périphérique-sud”) have seen their con­ges­tion increase by 15%, adding two min­utes on aver­age to commuter’s car jour­neys over a dis­tance of 10km. 

The prob­lem of con­ges­tion has there­fore just been moved from the banks of the Seine to the sub­urbs, where cit­i­zens are already expe­ri­enc­ing an over­all increase in res­pi­ra­to­ry com­pli­ca­tions among their res­i­dents. Accord­ing to a study con­duct­ed by the Air­parif asso­ci­a­tion², 5,040 pre­ma­ture deaths in the Greater Paris region and near­ly 7,920 in Ile-de-France were record­ed between 2017 and 2019. There is no indi­ca­tion that this increase is a direct result of the increase in con­ges­tion in the city, but it is cer­tain­ly not improv­ing the situation. 

Air pol­lu­tion has there­fore shift­ed, increas­ing the NO₂ con­cen­tra­tion in the air to 70μg/m³ around the east­ern ring road (“périphérique-est”) in 2015. Where­as, in the cen­tre, the pol­lu­tion rate remains around 40μg/m³. This indi­cates that areas which were already heav­i­ly affect­ed by pol­lu­tion prob­lems are becom­ing even more so and that the impact on health, although dif­fi­cult to quan­ti­fy, could be sig­nif­i­cant in years to come. 

Map of Paris show­ing expo­sure to pol­lu­tion³

Our analy­sis of the sub­ject⁴ seems to indi­cate that the rea­son why dri­vers do not change their mode of trans­port is because they are unable to do so. As the growth of pub­lic trans­port has not kept up with demand, pub­lic poli­cies penalise “trapped dri­vers” liv­ing in the sub­urbs who con­tin­ue to use their car due to the lack of alter­na­tives. It is there­fore cru­cial to inte­grate alter­na­tives into future mea­sures in order to have pos­i­tive long-term effects on the whole region and to avoid a per­pet­u­al shift in road congestion.

Oth­er solu­tions have been con­sid­ered abroad. Some cities, such as Lon­don and Seoul, have intro­duced con­ges­tion charges, the cost of which is cal­cu­lat­ed accord­ing to the aver­age impact of a vehi­cle in terms of con­ges­tion (i.e. “con­ges­tion charge” in Lon­don). How­ev­er, it is dif­fi­cult to apply such a fee in France, where polit­i­cal ten­sions around envi­ron­men­tal tax­es are very high. The increase in the car­bon tax in 2018, which was final­ly can­celled fol­low­ing the “Gilets jaunes” move­ment, is one of the most bla­tant exam­ples of the oppo­si­tion by the peo­ple of France to this type of tax­a­tion. More­over, it would serve to increase social inequal­i­ties because in France, unlike in oth­er coun­tries such as the Unit­ed States, the least well-off part of the pop­u­la­tion lives in the suburbs. 

There are a num­ber of ideas which could be imple­ment­ed to reduce con­ges­tion on the roads with­out aggra­vat­ing exist­ing social divi­sions, in par­tic­u­lar the idea of clos­ing and open­ing the river­banks at dif­fer­ent times of the day. In order to do this, it is nec­es­sary to con­sid­er how to opti­mise the use of the river­banks in rela­tion to the ameni­ties they pro­vide. Because, when the lanes are closed, they are used for eco­nom­ic pur­pos­es. For exam­ple, it could be ben­e­fi­cial to close off the Berges to traf­fic out­side of rush hour on week­days (8am-6pm) to ease traf­fic for com­muters work­ing in the cap­i­tal and at the same time allow for the use of ameni­ties which are not nec­es­sar­i­ly required dur­ing peak hours. 

How­ev­er, these solu­tions all entail dif­fer­ent costs, par­tic­u­lar­ly for open­ing and clos­ing the banks, which would require staff. The right solu­tions are com­plex and need to be care­ful­ly con­sid­ered so that all sides can find a solu­tion that ben­e­fits them. 

Interview by Fabien Roches