Elsevier

Atmospheric Environment

Volume 43, Issue 31, October 2009, Pages 4843-4854
Atmospheric Environment

The effects of congestions tax on air quality and health

https://doi.org/10.1016/j.atmosenv.2008.09.015Get rights and content

Abstract

The “Stockholm Trial” involved a road pricing system to improve the air quality and reduce traffic congestion. The test period of the trial was January 3–July 31, 2006. Vehicles travelling into and out of the charge cordon were charged for every passage during weekdays. The amount due varied during the day and was highest during rush hours (20 SEK = 2.2 EUR, maximum 60 SEK per day). Based on measured and modelled changes in road traffic it was estimated that this system resulted in a 15% reduction in total road use within the charged cordon. Total traffic emissions in this area of NOx and PM10 fell by 8.5% and 13%, respectively. Air quality dispersion modelling was applied to assess the effect of the emission reductions on ambient concentrations and population exposure. For the situations with and without the trial, meteorological conditions and other emissions than from road traffic were kept the same. The calculations show that, with a permanent congestion tax system like the Stockholm Trial, the annual average NOx concentrations would be lower by up to 12% along the most densely trafficked streets. PM10 concentrations would be up to 7% lower. The limit values for both PM10 and NO2 would still be exceeded along the most densely trafficked streets. The total population exposure of NOx in Greater Stockholm (35 × 35 km with 1.44 million people) is estimated to decrease with a rather modest 0.23 μg m−3. However, based on a long-term epidemiological study, that found an increased mortality risk of 8% per 10 μg m−3 NOx, it is estimated that 27 premature deaths would be avoided every year. According to life-table analysis this would correspond to 206 years of life gained over 10 years per 100 000 people following the trial if the effects on exposures would persist. The effect on mortality is attributed to road traffic emissions (likely vehicle exhaust particles); NOx is merely regarded as an indicator of traffic exposure. This is only the tip of the ice-berg since reductions are expected in both respiratory and cardiovascular morbidity. This study demonstrates the importance of not only assessing the effects on air quality limit values, but also to make quantitative estimates of health impacts, in order to justify actions to reduce air pollution.

Introduction

Many cities have implemented congestion charging or low emission zones aiming at reducing traffic congestion and health impacts of traffic emissions. In Singapore traffic congestion was alleviated using first a manual Area licensing scheme starting in 1975 and subsequently an Electronic Road pricing system (ERS) from 1998 (Seik, 2000). London has a road charging zone around the city centre that recently was updated to cover a larger area. Several Norwegian cities charge drivers travelling with studded winter tires in order to reduce particle emissions due to road wear. In Rome, traffic is prohibited in the inner city on weekdays. Several cities in Europe have low emission zones. In several Swedish cities low emission zones apply to trucks and buses. Recently three German cities (Berlin, Hannover and Cologne) have applied a complete ban on all vehicles that have no catalysts or diesel particulate filters in zones of the city centres.

However, so far, there are very few papers on the quantitative effects of road pricing or low emission zones on air pollutant concentrations, population exposure and health. Beevers and Carslaw (2005) analyzed the air pollution impact of the London congestion charging. Road traffic data, combined with a traffic emission model, indicate that NOx and PM10 emissions have been reduced by about 12% in the charging zone. But the emissions have increased on the inner ring road. The overall impact on air quality and health was not assessed. To our knowledge there is only one earlier study (Tonne et al., 2008) that has assessed the effects of a charging scheme not only on traffic and emissions, but also on exposure concentrations and health. They used a combination of dispersion modelling and regression calculations to analyse the air pollution and mortality benefits of the London congestion charge scheme (CCS). They concluded that the CCS lead to reductions in concentrations, although modest across Greater London, but greater in the charging zone wards. Predicted health benefits in the charging zone wards were 183 years of life per 100 000 people assuming conditions would persist over 10 years. This paper describes the effects of a road charge system in Stockholm on emissions, levels of air pollutants, and health of the population.

Section snippets

Description of the road charging system

On June 2, 2003, Stockholm City Council proposed testing congestion charging of traffic – called “The Stockholm Trial”. On June 16, 2004 the Swedish Parliament adopted a law that made it possible to charge a congestion tax in Stockholm up to July 31, 2006. The Stockholm Trial consisted of three parts: extended public transport (16 new bus lines), congestion tax and more park-and-ride sites in the city and the county. The total public transport service was extended by 7% and the park-and-ride

Measurements and modelling of road traffic

The effect of the Stockholm Trial on road traffic was quantified in terms of traffic flow by counting vehicles and by calculating road use, i.e. the number of vehicle kilometres travelled in the area (e.g. Baradaran et al., 2006, Forsman et al., 2006). Congestion was quantified in terms of journey times obtained from floating car measurements or from traffic cameras. Data on the composition of the vehicle fleet were acquired from manual recording of vehicle types over stretches of road where

Effects on traffic

Fig. 2 shows average traffic reductions for different types of roads. The reduction in total number of vehicle passages across the charge cordon over 24 h was 22%, corresponding to nearly 100 000 fewer passages to/from the inner city. The reduction was lower during the morning peak period (16%) and higher during the afternoon/evening peak (24%). For inner city streets the reduction in the number of vehicles was around 8% and for roads approaching the city around 5%. For the Essingeleden bypass,

Conclusions

The Stockholm Trial significantly reduced traffic emissions of NOx and particles in central Stockholm. The reductions were mainly due to decreased traffic flow; lower congestion had small effect. For NOx, emission reductions would have been larger without the extended bus traffic during the Stockholm Trial. Comparisons were made of NOx, NO2, CO and PM10 concentrations measured during the Stockholm Trial (the period January to July 2006), with the corresponding period in 2003, 2004, 2005 and

Acknowledgements

This work was funded by the Stockholm City Council.

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