Commit to enforce speed limits

That's how you do it

A lower maximum speed means lower vehicle emissions. The U-shaped relationship between traffic emissions and average speed is well documented, especially at constant speed (see image). The reported studies showed, as expected, that lower emissions improve air quality near busy roads.

In general, a speed limit improves the free flow of traffic and reduces traffic congestion, resulting in less exhaust emissions. When vehicles do not drive at a constant speed, but instead accelerate and decelerate frequently, you will not see this positive effect on emissions.

Lower emissions lead to lower concentrations of PM, NO ₂ and soot, resulting in corresponding positive health effects in the vicinity of busy roads.

• Particulate matter (PM) : The emission of PM ₁₀ decreases by 2 to 2.5 µg/m³ (about 8%). The drop for finer dust is more limited. Nevertheless, this result is better than what model studies expected.
• Nitrogen dioxide (NO ₂ ) : The reduction in NO _x emissions ranges from negligible to 30%. A temporary increase in the maximum speed caused the NOx to _rise again by 20%.
• Soot (EC) : A 10% drop was noted for carbon black. A temporary increase in the maximum speed resulted in an increase of 17%. Model studies expected greater effects near highways.
• Other : In some cases there was less traffic congestion, in other cases the flow did not change. Decreases of 21% were observed for carbon monoxide (CO).

Implementing speed limits also offers these advantages :

• Fewer traffic accidents and casualties
• Reduction of noise pollution
• The number of traffic jams is decreasing
• Lower fuel consumption, and associated lower greenhouse gas emissions.
• Higher life expectancy for those living near highways

Knowing more

Speed reduction measurements

Amsterdam, Netherlands -2008

In Amsterdam, a speed limit was introduced on a part of the A10 that runs through a residential area. Measuring stations registered particulate matter, nitrogen oxide (NO _x ) and soot. For comparison, the researchers also measured the air quality on a section of the A10 where the maximum speed had not been reduced. ( Dijkema et al. 2008 ).

Speed reduction measurements

Rotterdam, Netherlands - 2003-2014

In 2003, the maximum speed on the A13 was increased from 100 to 80 km per hour on a strip of 3 kilometers. For political reasons, the speed limit was raised again to 100 km/h in 2012. A 2014 court decision reduced the speed again to 80 km/h. An automatic section control ensured the enforcement of the speed limit, except in the period 2012-2013. The concentrations of PM ₁₀ , CO, NO _x and CO ₂ were investigated at various distances from the highway ( Wesseling et al. 2003 ). Both before and after the speed limit, traffic flow and air quality were also examined. ( Willers, 2013 ).

Effect of Speed Limit & Traffic Light Coordination on Vehicle Emissions

Flanders, Belgium - 2011

In Flanders, model studies were performed with speed limits on highways ( Levbre et al. 2011 ) as well as in residential areas ( Madireddy et al. 2011 ).

Speed Limit Studies

Barcelona, Spain - 2007-2013

Two studies examined the impact of both fixed and variable speed limits (introduced in 2007 and 2009) on congested parts of urban highways in Barcelona. ( Germa Bel et al., 2015 ; Baldasano et al., 2010 ).

More information

• Clear results and a comprehensive, useful strategy can be found in: Air quality effects of an urban highway speed limit reduction .