using data from a diverse sample of commuters working in Cambridge, UK. We evaluate whether GIS can produce routes that adequately reflect the characteristics of the actual routes taken using a set of commonly assessed metrics, and ascertain the circumstances under which GIS-derived shortest distance path routes may reflect those actually taken either particularly well or poorly. We identify circumstances in which modelled routes could be useful proxies for actual journey characteristics, and suggest implications of our findings for the assessment of environmental exposures.