Estimation of the Optimum Speed on Urban Residential Streets
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. Three different methods were considered to measure the impact of travel speed on road trauma and/or crash costs. Relationships between cruise speed and average (all) speed 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. Air pollution emission rates at each travel speed were based on European relationships. The project focused on urban residential streets with 60 kmh speed limits because of the availability of a considerable amount of relevant basic data. When the ?human capital? valuations of road trauma costs 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, the analysis suggested that the optimum speed on residential streets is 50 kmh. The analysis presumed that it is legitimate to adopt an economic rationalist approach to choose the optimum speed in residential streets. If the value of road trauma was five times the ?human capital? costs, 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).