2.2. Study areas

To allow for controlled comparisons, we iteratively delineated three study areas in Glasgow using a Geographic Information System (GIS). The study areas were defined as census output areas (the smallest unit for which census data are available) lying wholly or partly within a 500 m buffer surrounding the proposed new M74 motorway extension (South study area), the existing M8 motorway (East study area) and the suburban railway between Cowlairs and Maryhill (North study area containing no motorway).

Aggregate census data, including levels of deprivation and unemployment, home and car ownership, and prevalence of chronic illness, were tabulated for the South (new motorway) study area. The boundaries of the East (existing motorway) and North (no motorway) study areas were then iteratively adjusted using a GIS until they matched the South (new motorway) study area on these characteristics (Table 1). During this process, field visits were conducted to ascertain the general characteristics of the built environment in the three areas, to confirm the face validity of the general comparability of the study areas and aid in producing the final boundaries. All three study areas extended from near the city centre to residential suburbs, contained other major arterial roads, had a mixture of housing stock and had broadly similar socioeconomic characteristics, but differed in their proximity to motorway infrastructure (Fig. 1) (Ogilvie et al., 2008).

Boundaries of local study areas in Glasgow at baseline (2005) defined in terms of census output areas. Dotted line shows route of M74 motorway extension. Data and raster image © Crown Copyright/database right 2005. An Ordnance Survey/EDINA supplied service.

Aggregate sociodemographic characteristics of study areas using 2001 census data.

NS-SEC – National Statistics Socio-economic Classification.

North – study area containing no motorway infrastructure; East – study area containing existing M8 motorway; South – study area containing new M74 motorway.