Land-use and transport systems are an important determinant of carbon dioxide emissions from urban regions. It is often asserted that urban compaction is the spatial policy best able to constrain travel and emissions, but evidence supporting this assertion is limited, particularly with respect to the combined emission from transport and land use. Here, using land-use-transport interaction models, a residential dwelling type model, and transport and emission models, we forecast and assess carbon dioxide emissions from transport, dwellings, and commercial space to 2031 for a range of spatial strategies realistically investigated for three English regions of decreasing size (the Wider South East region, Tyne and Wear, and Cambridge). Our results reveal that compaction can reduce emission relative to other spatial scenarios but that the differences are small, about 5% between extremes, an order of magnitude less than emission growth observed over the trend period. Form has more influence for settlements where the pattern and proximity of employment, housing, and services can make cycling, walking, and public transport provision more feasible. We conclude that pricing and technology measures offer better prospects for combating the growth in carbon emissions of urban regions, but that the type of urban form delivered is likely to be a significant determinant in the type of clean energy technology that can be implemented.