Clear Roads and Dirty Air? Indirect effects of reduced private traffic congestion on emissions from heavy traffic.

Traffic and transportation are a major source of CO 2 emissions. As the volume of heavy goods vehicle (HGV) transportation is difficult to reduce, many governments target private traffic. Next to the direct effect of fewer private vehicles on the roads, an indirect effect may be very important: The less congestion, the more fuel-efficient the remaining drivers may be able to drive because there would be less need to speed up, brake, and maneuver, for example while overtaking. On the other hand, clear roads may be tempting for drivers to speed and thus result in a negative impact of less private traffic. The direction and size of this indirect effect is difficult to measure for two reasons: First, we usually have no real-time driving data from heavy trucks. Second, traffic density usually does not vary to a large extent. We set out to assess the margins of this indirect effect using a unique data set from a large German logistics fleet. We measured truck drivers' driving behavior as well as emissions from their trucks between January and May 2020. During that time, the COVID-19-related policy measures led to a significant decline in private traffic on highways. We find that less private traffic volume results in improved fuel-efficient driving behavior, resulting in reduced overall CO 2 emissions. The effect is u-shaped; too little private traffic density leads to less fuel-efficient driving by the remaining heavy goods vehicle drivers. Moreover, removing the worst drivers from the roads has the same effect in terms of magnitude as reducing private traffic congestion to the medium-density optimum. • Policies targeting car traffic may backfire depending on truck drivers' responses. • Low traffic may result in fuel-efficient driving or speeding of truck drivers. • We use unique data including the actual behavior of about 700 German truck drivers. • We find a u-shaped relation between traffic density and truck emissions. • Optimal traffic density reduces emissions like removing the worst 10% of drivers. [ABSTRACT FROM AUTHOR]