Air pollution is a big problem in Portsmouth. To plan for the future, we need to know if the problem is getting better or worse, and by how much. One of the biggest contributors to air pollution is local traffic.  A 2010 report commissioned by Portsmouth City Council found that a significant increase in traffic was expected:

Traffic in Portsmouth is expected to grow by 41% between 2009 and 2031 due to a combination of housing and employment related trips that will be attracted and generated by the proposed development sites in the City. […] The forecast impact of the additional demand generated by new development, not only in Portsmouth, but surrounding local authorities would lead to a 41% increase in traffic on the approaches to the City. More importantly a significant proportion of that increase would occur on the M275/Western Corridor. (Western Corridor Transport Study, 2010)

Portsmouth City Council (PCC) operate a number of nitrogen dioxide (NO2) and particulate monitoring stations. The legal limit for NO2 is 40μg/m3 (micrograms per cubic metre). More traffic is a cause of concern in high pollution areas, including along the western corridor M275/Mile End Road/Market Way/Anglesea Road, specifically:

  • Stanley Road (by the M275), 36μg/m3 NO2 in 2016 (which is increasing year on year)
  • Sovereign Gate (Commercial Rd) 36μg/m3 NO2 in 2016
  • Lord Montgomery Way, already 43.5μg/m3 NO2 in 2016 (which is increasing year on year)

An increase in 41% in traffic levels would be disastrous for air quality in Portsmouth and push these areas into an illegal and unsafe level of pollution.

However, a 2017 study commissioned by Portsmouth City Council to determine the scale of the air pollution problem in 2020 only allowed for a 2.1% rise in city wide traffic from 2015 to 2020. This seems to be inconsistent with the 2010 traffic report. Based on the 2017 study, Portsmouth City Council hopes that the introduction of less polluting vehicles will bring the city within legal pollution limits. If the 2017 traffic projection is wrong and we do see a large increase in traffic, we would likely see air pollution get even worse. PCC seem to want to have it both ways: to build new roads for higher traffic levels at the same time as claiming traffic levels are not significantly increasing.

Portsmouth City Council is currently planning a major road scheme in the city centre, intended to reduce congestion by increasing capacity. It is currently at the planning application stage (please go there and comment! [Update: I am told that the closing date for comments is Friday 12th Jan]). However, simply increasing road capacity is only going to worsen air quality. What we need to do instead is to reduce car usage by providing alternatives, including public transport and bicycle routes.