Estimating intra-metropolitan journey-to-work CO2 emissions: a multi-modal network approach applied to the London Region 2001

This paper develops a methodology for estimating network distances and CO2 emissions for UK census ward-level journey-to-work interactions. Improvements are made on existing empirical measures by providing comprehensive intra-metropolitan analysis; increasing network routing accuracy with UK public transport timetable and GPS-based average road speed data; allowing multimodal travel; and developing metrics suitable for travel sustainability analysis. The output unit of CO2 emissions has been selected to enable the integration of mode-choice and travel distance data, and to aid compatibility with integrated assessment applications. The methodology is applied to the case study of the London Region for the year 2001. A very high degree of intra-metropolitan variation is identified in the results. Employment sub-centres diverge in their per-capita CO2 emissions by up to 300%, with specific problems of carbon intensive commuting to major airports and the specialised employment region of the Western Sector. These findings indicate that subcentre travel variation may be intrinsic to polycentric urban structures. The paper discusses means to improve the methodology, in relation to issues of coefficient disaggregation and modelling more complicated multi-modal trips