The change in carbon dioxide emissions was estimated as part of the evaluation of the M25 J15-16 controlled motorway scheme. The variable speed limits were operational in the morning (7am to 11am) and evening (3pm to 7pm) peak periods. The assessment showed a reduction in carbon dioxide emissions of 4.5 per cent. on the northbound section and a reduction of 2.9 per cent. on the southbound section during the peak hours. This translates into a potential weekday saving measured over a calendar year of 1,184 tonnes of carbon dioxide for J15-16.
Changes in other years and on other sections are expected to be similar.
(2) what estimate she has made of the effect on carbon dioxide emissions if the maximum speed for hard shoulder running in the modelling for the advanced motorway signalling and traffic management feasibility study were reduced from 60 mph to 50 mph.
All traffic modelling of the impacts of hard shoulder running undertaken as part of the advanced motorway signalling and traffic management feasibility study was carried out on the basis of a 60 mph speed limit during operation of the hard shoulder as a running lane.
The additional modelling undertaken to ascertain the effects on emissions of the smoothing of the traffic flow brought about by the imposition of controlled lower speed limits and hard shoulder running was done using average speed emissions curves based on actual data collected during the M42 pilot, which operated a 50 mph limit for hard shoulder running. It was not possible to provide a comparison with a 60 mph limit.
Following detailed safety assessment, hard shoulder running with a 60 mph speed limit is the standard to be adopted for future hard shoulder running schemes, starting with the M42 where this has been operational since 18 March. As a larger data set for hard shoulder running becomes available, the speed emissions relationships will be reviewed.
Further detail on the modelling undertaken is set out in the advanced motorway signalling and traffic management feasibility study report and technical annex, which are available on the DfT website at: