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Highway Pollutants



Highway Pollutants

Background & policy context: 

One of the consequences of the continuing increase in road transport has

been the growth of pollution, both atmospheric and ground based. Efforts

have been made by policy makers, engineers, scientists and the public to

reduce the environmental impact of transport. European work in this area

has advanced, however, in a fragmented way. Past objectives have been to

solve particular problems, often concerning a specific pollutant and/or

section of the environment, in individual countries.

  • The aims of the POLMIT project are to:
  • determine and understand the absolute and relative importance of highway pollutants compared with other pollutant sources;
  • understand the dispersal mechanisms of these pollutants and the pathways by which they are released to soil and groundwater;
  • understand the physical and chemical impacts of highway pollutants on soil and groundwater - both locally and nationally;
  • identify/developing practical measures which may be taken to control, or mitigate this pollution.

To achieve the aims, the project will involve:

  • two case study sites in each of the seven participating countries; to cover a range of conditions and particular problems encountered throughout Europe;
  • identification of factors that influence the emission and transportation processes;
  • calculation of mass fluxes of pollutants; identification of the most important pathways for each pollutant under varying local conditions, such as traffic density and climate etc.;
  • collation of existing data and development of a computerised database; using literature and experimental data;
  • calculation of mass balances of pollutants at local, and on national and European scales; mitigation measures, Best Practice Guide and Policy Advice.
Institution Type:
Institution Name: 
European Commission; Directorate-General for Energy and Transport (DG TREN; formerly DG VII)
Type of funding:
Key Results: 

Metal emission rates have been primarily dependent on traffic volume, PAH (Policyclic Aromatic Hydrocarbons) emission rates primarily on traffic volume and road type, chloride emission rates mainly on the severity of the winter during the monitoring period and hence on the application of de-icing salts. Comparison with reported atmospheric emission in the UK has indicated that road transport contributes little Cd or Cr, very small amounts of Cu (2%) but significant amount of Pb (59%) and Zn (23%).

A mass balance approach has been used to determine what proportion of the calculated pollutant emissions entered the local terrestrial roadside, through highway runoff or aerial dispersion. The transfer rates of PAHs have been generally 10% of the emissions; within the metals, Zn was transported in the greatest quantity, followed by Cu and Pb and finally by Cr and Cd. Recovery rates for Cu and Pb have been relatively low (less than 10% and 5% respectively) while the rate has been just below 50% for Zn.

To determine the significance of roads and vehicles to soil and groundwater pollution, concentrations of road/vehicle-derived substances have been compared with recognised threshold levels, namely the intervention and target levels as set in the Dutch legislation. Soil intervention levels have been exceeded only for Pb, because of the large use of leaded fuel in the past. Most of the metal concentration have resulted well below the Dutch intervention levels for groundwater.

Policy implications

When an assessment indicates the need for treatment of road and vehicle pollution, the selection of the most appropriate type of treatment will have to take account of the type of pollutant, the transport mechanism by which this pollutant enters the roadside environment, the availability of land, the physical characteristics and the qualities of the receiving environment. Mitigation actions can be grouped into source-based and effect-based measures. Only source-based measures can tackle pollution that is transported by aerial dispersion.

The POLMIT project has developed the first draft of a Best Practice Handbook for the assessment of potential pollution problems and identification of the most appropriate treatment strategies. Further work would be needed to develop this handbook into a practical guide for engineers and consultants, to address some of the inconsistencies found in the experimental data and to identify clear thresholds within the decision making process.


Transport Research Laboratory (UK); Directorate General for Public Works

and Water Management (NL); Swedish Road and Transport Research Institute

(SE); Technical Research Centre of Finland (FI); Danish Road Institute

(DK); Laboratoire Central des Ponts et Chaussées (F); Laboratório Nacional

de Engerharia Civil (PO).

Contact Name: 
Dr Adine Hird
Contact Email: 
Transport Research Laboratory
Old Wokingham Road
RG45 6AU
Contact country:
+44 1344 770351
Fax Number: 
+44 1344 770918