For CO2, similar issues apply at both strategic and project level. At the project level, more spatially defined traffic models may be used and this may remove some of the issues detailed above. Total CO2 emissions for road traffic can be calculated according to the method in DMRB 11.3.1. For rail Transport Scotland recommends the use of the Rail Emission Model Final Report that was produced for the Strategic Rail Authority.
Walking and cycling schemes which divert users from other modes will impact on this criterion. It is recognized that in many cases practitioners will not have access to a local road network model to assess these impacts. Transport Scotland is currently reviewing guidance in this area, but in the interim practitioners should make use of the road network effects approach in Section 9.5.23.
