Densification plays important role in environmental and human health gains in low-dense high-income cities. Increasing walk and cycle without densification, however, provide human health benefits mainly.

For the attention of: Metropolitan planning authorities, departments of transportation, urban designers and public health researchers.

The problem: The transportation sector accounts for approximately 23% of total energy-related carbon dioxide (CO2) emissions worldwide and 33% in the USA.  At the same time low levels of physical activity contribute to the burden from non-communicable diseases.

If policies can increase active transport (walking and cycling) and reduce car use they could benefit population health and reduce CO2 emissions but the relative impact of different approaches has been under researched.

What we did: We estimated reduction in CO2 emissions and health co-benefits in greater Nashville for two scenarios:

(a)  if people in Nashville were as likely to walk and cycle a trip of a given distance as are people in England,

(b) if there was a more compact urban form reducing travel distances and indirectly increasing walking and cycling trips.

Both these measured benefits would be helpful in forming sustainable urban societies.

What our study adds: Our work is based on the estimates of health and environmental benefits at disaggregated data using a much larger individual level dataset than is available for most city regions. This provides more realistic results than the models based on linear and population level data. The propensity approach takes the real behaviour of a population in another highly motorised society and using a compact urban form scenario we modelled trip distance and mode choice against Nashville’s existing density.

Implications for city policy and practice: Our scenarios, as policy goals, should help in city-to-city policy learning. Policy changes to increase propensity to walk and cycle could occur more rapidly than substantially increasing density. From a population health perspective, our findings should be encouraging in that important gains could be realised from increasing active travel even in a sprawling city.

Full research article: A comparison of the health and environmental impacts of increasing urban density against increasing propensity to walk and cycle in Nashville, USA

Authors: Sohail Ahmad (@sohailplanner), Anna Goodman, Felix Creutzig (@efesce), James Woodcock, Marko Tainio (@MarkoTainio)
Editor: Marcus Grant