Impact on vehicle speeds and pollutant emissions of a fully automated section speed control scheme on the Naples urban motorway

摘要

Section speed enforcement systems are becoming established as cost-effective measures toreduce the incidence of speeding and thus improve road safety. It is also widelyacknowledged that speed levels affect pollutant emissions. Therefore, significant co-benefitsin environment and road safety are expected from the application of such systems. Yet fewstudies have investigated the environmental effects of speed limit reduction and even fewerthose of tight speed limit enforcement.In this study an empirical analysis is carried out to investigate the impact of a new 80km/hspeed limit and tight enforcement on an urban motorway in Italy. First a detailed analysis ofindividual-vehicle section speeds (i.e. section travel times) is performed. The study focuses onseven motorway sections and three reference periods, namely weekday peak hours, free-flowhours and the entire week. This allows the effect of road geometry and traffic conditions to beevaluated as well. Secondly, thorough calculation of pollutant emissions and fuelconsumption is carried out. As it is based on individual vehicle speeds, the effect of changesin speed variance among drivers is also captured. This turned out to be relevant to theapplication.Basically, study outcomes suggest that the strategy can be a straightforward and effectivepolicy to put eco-driving principles into practice, only in network stretches or in time periodsin which congestion is not too heavy. Therefore, for such systems the opportunity forsignificant co-benefits in fuel economy and road safety appears to exist only under these strictconditions.