7 The locations of the road links with the highest predicted concentrations

The objectives for 2005 within the NAQS (DoE, 1997) apply to non-occupational near-ground level outdoor locations where a person might reasonably be expected to be exposed over the relevant averaging period. The annual mean NO2 objective of 21 ppb therefore only applies at the facade of buildings where people actually live. NO2 concentrations are expected to fall rapidly as the distance from the road increases reaching levels similar to background at distances greater than 20-30 metres (QUARG, 1993). The modelled estimates of roadside NO2 concentrations presented in this report have been calibrated by reference to automatic monitoring sites within the national monitoring networks. The estimated concentrations are therefore representative of concentrations at distances up to about 5 m from the edge of the road. We have carried out a preliminary assessment of the likely presence of housing at the roadside of the links with the highest estimated concentrations in 2005.

Table 7.1 lists the top 50 or so road links outside London with the highest estimated roadside NO2 concentrations in 2005. The roads are sorted by city and ranked by concentration within each city. Estimated concentrations for the business as usual (a) and 30% less traffic emissions (h) and 30% less emissions from cars (i) are shown. The likelihood of housing within about 10 m the roadside was assessed by contacting local authority representatives and studying maps. Many of the road links listed in Table 7.1 are unlikely to have people living close to the road, although there are a number of roads with houses present. It should be emphasised that this is only a preliminary assessment and this should be addressed in detail by local authorities carrying out a review and assessment for roadside NO2.

The built-up road links with estimated concentrations in excess of 21 ppb in 2005 are almost exclusively confined to cities in England. Two of the four links in Scotland have concentrations high enough to be included in Table 7.1. Stobcross street is a largely commercial area, with a few flats at an unknown distance from the road. The Clydeside Expressway looks like a commercial area on the map. The other two road links are the A739 Clyde Tunnel and the A725, which is a by-pass near Hamilton. Neither of these links are expected to have housing within 10 m. The only road link in Wales with estimated concentration greater than 21 ppb is the A4051 in Malpas near Newport. This road has been by-passed by a new road which avoids the urban area since the road links database was compiled and is therefore unlikely to present a problem in 2005. Detailed information on the split between built-up and non-built-up road links is not available for the major roads in Northern Ireland. The only non-motorway links with estimated concentrations greater than 21 ppb in 2005 are the A12 West Link and A55 University Road/Malone Road in Belfast. The likelihood of housing close to these roads has not been assessed.

We have not assessed road links in London for the presence of housing but it is likely that people will be living close to many links with estimated concentrations greater than 21 ppb in 2005. Background concentrations in inner London are also expected to be at risk of exceeding 21 ppb in 2005 for the business as usual scenario, so the presence or absence of housing close to a particular road is less important. Details of the locations of the roads with the highest estimated concentrations in Inner and Outer London are given in Table 7.2 and Table 7.3