The optimum speed is defined as one which balances the social costs and benefits of increased travel time with decreased road trauma, vehicle operating costs, emissions, etc. The project focused on urban residential streets with 60 kmh speed limits because of the availability of a considerable amount of relevant basic data. Three different methods were considered to measure the impact of travel speed on road trauma and/or crash costs (Kloeden et al 1997, Nilsson 1984, Kallberg and Toivanen 1998). The relationships between cruise speed and average (all) speed found by SMEC (1998) were extrapolated to measure the impacts on travel time in residential streets for travel speeds in the range 35 to 85 kmh. The relationship between vehicle operating costs and travel speed was based on two Australian models given by Thoresen (2000). Air pollution emission rates at each travel speed were based on European relationships given by Ward et al (1998). The analysis made use of a modification of a computer spreadsheet developed as part of the European project MASTER (MAnaging Speeds of Traffic on European Roads). When the “human capital” valuations of road trauma costs (BTE 2000) were used, the analysis suggested that the optimum speed on residential streets is 55 kmh. When the analysis was repeated making use of road trauma costs valued by the “willingness to pay” approach (BTCE 1997), the analysis suggested that the optimum speed on residential streets is 50 kmh. The analysis described in this report has presumed that it is legitimate to adopt an economic rationalist approach to choose the optimum speed in residential streets. If the values of road trauma costs were five times those estimated by BTE (2000), a travel speed of 35 kmh would be the maximum speed which could be economically justified. This is close to the maximum speed which has been demanded by societies not wishing to compromise road safety and aiming to prevent all deaths and serious injuries on residential streets (30 kmh). (Author/publisher)
Abstract