Green Infrastructure for Roadside Air Quality (GI4RAQ) guidance & decision tree: an evidence-based approach to reducing roadside exposure to road transport pollution

Research output: Working paper/PreprintWorking paper


Green Infrastructure for Roadside Air Quality, ‘GI4RAQ’, is an initiative by Dr James Levine and Prof Rob MacKenzie at the Birmingham Institute of Forest Research (BIFoR), University of Birmingham, to promote and facilitate evidence-based use of green infrastructure to reduce roadside exposure to road transport pollution. The GI4RAQ Guidance document describes the development of an evidence-based, albeit qualitative, approach to GI4RAQ with Yvonne Brown, Principal Policy Analyst for Air Quality and Climate Change at Transport for London (TfL). It includes essential guidance on the use of the GI4RAQ Decision Tree – a differential diagnostics approach, visualised using a PowerPoint Show with embedded links. Whilst the approach has been developed for TfL and refers to case studies in London, both this guidance and the GI4RAQ Decision Tree are applicable to roads in all towns and cities, and the authors hope that these resources will find widespread use.

The GI4RAQ Decision Tree guides the user through a short series of questions to identify the critical characteristics of the street in which they are seeking to reduce roadside exposure to road transport pollution. Subject to these characteristics, 'robustly beneficial' green infrastructure interventions are identified, as well as ones 'potentially beneficial to some at the expense of others'; the terms in inverted commas will be explained in due course. The accompanying guidance, provided here, builds on the “Reduce, Extend, Protect” concept introduced in the Trees & Design Action Group’s guide, ‘First Steps in Urban Air Quality for Built Environment Practitioners’ (Ferranti et al., 2019): first reduce the emissions of pollutants, then extend the distance between people and the sources of these emissions (i.e., vehicles) and, finally, protect those most vulnerable to their health impacts. This guidance is also consistent with, but elaborates on, that recently published by the Greater London Authority, ‘Using Green Infrastructure to Protect People from Air Pollution’ (GLA, 2019).

Within TfL, this evidence-based approach to reducing exposure to road transport pollution supports TfL’s Healthy Streets Approach in putting people and their health at the centre of design decisions and the use of public space; it is also integrated into TfL’s Environmental Evaluation Tool, designed to capture and manage the impacts of projects not requiring a full Environmental Impact Assessment under Town and Country Planning Regulations 2017 (MHCLG, 2017). ‘Clean air’, however, is just one of ten positive outcomes sought via TfL’s Healthy Streets Approach, and green infrastructure contributes to a further eight (see ‘Indicators Explained’ section of Healthy Streets Check for Designers spreadsheet). Likewise, whilst this guidance focuses on improving roadside air quality, we recognise that green infrastructure can (simultaneously) deliver further, major benefits; we will highlight the opportunities for co-benefits throughout the document. Improved air quality is just one benefit of – and one consideration in – the planning, planting and investing in green infrastructure for the long term.
Original languageEnglish
PublisherUniversity of Birmingham
Publication statusPublished - May 2021


  • urban forestry
  • green infrastructure
  • GI
  • vegetation
  • barrier
  • planting
  • natural capital
  • nature based solution
  • NBS
  • air quality
  • air pollution
  • dispersion
  • emission
  • exposure
  • impact
  • nitrogen oxide
  • NO2
  • particulate matter
  • PM
  • PM2
  • public health
  • roadside
  • road
  • street
  • public realm
  • road improvement
  • scheme
  • road transport
  • vehicle
  • planning
  • town planning
  • urban design


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