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