Vehicles: traffic jams are bad for energy consumption and CO2 emissions

Traffic congestion is not good for the environment. Studies in Japan for passenger vehicles have shown that that CO2 emissions are roughly stable for an average speed between 30 km/h and 90 km/h with an emission  value between 100 and 140 gCO2/km. It increases a little bit above a speed around 90 km/h. There is however a strong increase at low average speed, that is during high traffic congestion. For example at an average speed of 10 km/h CO2 emissions are above 200 gCO2/km. Traffic congestion is therefore very bad for CO2 emissions and energy consumption. In Paris, but also in other cities, some people think that organizing the traffic in such a way that the average speed decreases would encourage people using public transportation. This is however a wrong idea. In the Paris region about 80% of people use their car and 20% public transportation. The present public transportation would not be able to accomodate 5% more people (those moving from their car to public transportation) because the public network would be oversaturated.

Now concerning freight transportation, it is also important that trucks deliver their goods away from peak hours. A German study has shown that, during traffic congestion, a truck would consume in the average 28 l/100 km at a speed of 50 km/h without stopping. If the truck stops once every km the fuel consumption rises to 52 l/100 km and it reaches 84 l/100 km if it stops twice every km.

Data from IEA (www.iea.org): transport, energy and CO2