Air quality issue

In Berlin, the EU annual air quality limit value for NO2 of 40µg/m3 was persistently exceeded on several main roads with heavy traffic in the period from 1990 up to 2020. Road traffic accounted for 75% of emissions causing these exceedances.

Example of measures taken

In response, the speed limit on five polluted roads, along a total length of 8.5km, was lowered from 50km per hour to 30km per hour. This measure aimed to:

  • smooth the flow of vehicles
  • cut emissions of nitrogen oxides (NOX)
  • reduce noise.

This speed limit was first introduced as a trial, accompanied by the monitoring of NO2 levels (using passive samplers), traffic flow and traffic speed.

The trial was deemed successful, resulting in a reduction of 2-4µg/m³ in annual average concentrations of both NO2 and coarse particulate matter (PM10). Noise levels were reduced by up to 2 decibels. The measure benefited approximately 7,500 residents living along the roads. Building on this success, a permanent 30km per hour speed limit was put in place.

Costs and trade-offs

The pilot cost €850,000. This covered the costs of supplementary traffic count units, a mobile air quality monitoring device, road signs, traffic light coordination and evaluation of the data collected.

The speed restrictions resulted in longer travel times for public buses and private cars. More buses were needed to maintain the service level, costing €620,000 per year. No diversion of traffic was observed.

Who was involved?

The measure was implemented by the Berlin Traffic Management Unit together with the Department for Environment, Transport and Climate Protection. They were supported by a working group, including the unit for air quality monitoring, the unit for noise action planning, the road traffic authority, the public transport company, the police and the administrations of the relevant Berlin districts.

Before the revised air quality plan was adopted, a public consultation was held as well as meetings with key stakeholders, including non-governmental organisations, the Berlin chamber of industry and commerce, and taxi and freight associations.

Lessons learnt

  • Speed reduction measures are easy and cost-efficient to implement.
  • Traffic light coordination should be adjusted to smooth traffic flows and avoid acceleration, which leads to spikes in NOX emissions. How this is done depends on road structure, in particular the number of junctions and the distance between them.
  • Speed limits can improve air quality if the initial level of congestion is not too high. At one pilot street, no improvement was seen, as vehicle speeds were already very low.
  • Transparent communication with the public is essential for raising awareness and ensuring compliance with speed limits. Displays showing the speed of passing vehicles helped to increase the compliance rate.
  • NO2-passive measurements have a low temporal resolution of 2-week averages. A higher temporal resolution of air quality measurements would have enhanced the assessment of the relationship between short-term NO2 fluctuations and traffic patterns.

Berlin, Germany
Type of measure
Regulatory measure to control traffic speed
Target pollutants
Nitrogen dioxide (NO2) Nitrogen oxides (NOX)
Particulate matter with a diameter of 10 microns or less (PM10)
Pollution source targeted
Road traffic
A short description of the 30km/h traffic trial can be found here (in German)
Evidence of the impact of 30km/h speed limits on main roads (in German)
Air quality plan from 2019


Geographic coverage




Filed under:
Filed under: road traffic
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