In December 1995 Gloucestershire County Council was awarded £5m by the Department of the Environment, Transport and the Regions to reduce the number of road casualties in Gloucester by implementing a coherent range of traffic management and traffic safety measures according to a well-defined strategy. The strategy became known as the Safer City Project. TRL is monitoring the effects of the different measures on accidents, traffic distribution and speed, vehicle emissions and air quality, vehicle and traffic noise, vibration, and public perception of the environment. This report deals with the effects on vehicle emissions. Detailed surveys of passenger car driving cycles, traffic flow, and traffic composition have been made to assess the changes in emissions along a sample of links in Gloucester which are likely to be affected. These surveys are being repeated at annual intervals, and the report presents the results of the first three. These were conducted in November of 1996, 1997, and 1998. The links were arranged into groups according to the main (or only) type of traffic management or traffic safety measure that was implemented during 1996-97. The measures investigated were anti-skid surfacing, gateways, a roundabout, speed cameras, pedestrian refuges, and carriageway narrowing combined with a cycle lane. On two links where measures had been introduced during the 1996-97 period, a broad range of measures were also introduced during 1997-98. Consequently, these links were treated separately. A sample of links on which no traffic management measures had been introduced was also considered. The calculation of emissions on each link was either a one-step or two-step process, depending upon the level of information available. For all 76 links where driving cycles had been recorded, emissions from LDVs in each year were estimated using the driving cycles as an input to the MODEM emission model. Emissions from HDVs were calculated using empirical emission functions for heavy goods vehicles relating to average link speed. For the sub-sample of links where traffic flow and composition had been recorded, weekday emissions from traffic were estimated by weighting the emissions from LDVs and HDVs by the traffic flow and composition. For each type of link, an assessment was made of the relative importance of the different factors contributing to the changes in traffic emissions. (A)

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