This post is about the local impact of city centre road scheme on NO2 pollution levels in 2026, which is the year the scheme is expected to be completed. The scheme’s effect on pollution was predicted by wsp consultants for Portsmouth City Council using computer models.

Upward (red) arrows indicate an increase in pollution, downward (green) arrows indicate a reduction in pollution. Circles indicate negligible impact. Traffic levels and vehicle efficiency are expected to change over time but this map simply compares the “with scheme” 2026 scenario with the “no scheme” 2026 scenario. This shows is the effect of the scheme itself, rather than these other traffic changes.

References: wsp consultants, City Centre Road Project, Addendum to Environmental Statement, Appendix A.6, April 2018, Revision 3

As can be seen, pollution decreases in a handful of areas, particularly at the north end of Commercial Road, and some parts of London Road/Kingston Road. However, pollution increases in many more areas, particularly around the university and Gunwharf Quays. This scheme should be of particular concern to people living and working in these areas, which are already near the legal limit for NO2 (as shown in a recent post).

The wsp report provides further detail:

The scheme is predicted to cause exceedances of the objective at two receptors (Receptor R20 – B2154 The Hard and Receptor R27 – A3 St Michael’s Road) but will reduce concentrations to below the objective at three receptors (Receptor R64 – A2047 Kingston Road, Receptor R65 – A2047 Kingston Road and Receptor R94 – Old Commercial Street) in this scenario.

The largest increase in concentrations was 5.4μg/m 3 , predicted at receptor R92 (Stanhope Road), however the “With Development” total annual mean concentration at this location was below the objective at 36.2 μg/m 3. The largest decrease in concentrations was 8.8μg/m 3 predicted at receptor R94 (Old Commercial Road), which reduces the total 2026 “Without Development” annual mean NO 2 concentration from 49.3μg/m 3 to 39.3μg/m 3.

It should be noted that although there are a small number of substantial adverse impacts predicted to occur, these all occur in the same geographical location; to the south of the Proposed Development around Stanhope Road/Edinburgh Road and the A29 St Michael’s Road.

The locations at which substantial beneficial impacts occur include receptors near to the junctions of Kingston Crescent and Lake Road. Receptors R89 (A3 Marketway) and R94 (Old Commercial Street) also see a significant drop in concentrations as a result of the new road alignment nearby.

With some areas being pushed above the 40μg/m3 legal pollution, it is arguable that the scheme violates UK air quality law. Areas that are close to or above the limit are at significant risk of health problems. The council needs to reconsider the scheme and attempt to provide significant overall reductions in NO2 levels across the city. This road scheme seems to make things generally worse.