To assess vehicle-level effects of traffic measures like extra lanes and changes to crossroads geometry, the Dutch Transport Research Centre (AVV) uses a computer model called FLEXSYT that calculates not only impacts on traffic flow but also the environmental impact of various scenarios. The environment module of FLEXSYT was outdated, however, and AVV therefore asked CE to perform an update, while retaining the current formulae as far as possible.
The model consists of formulae derived from a series of empirical models describing vehicle emission characteristic. These formulae comprise two kinds of parameter: general parameters (vehicle fleet data, for example) to calculate the emissions of particular vehicle flows, and empirical model parameters describing the relationship between fuel and energy consumption and emissions. The updating process comprised two parallel activities.
The general parameters were updated using statistics from several sources, including Netherlands Statistics (CBS) and the Dutch Traffic and Transport Taskforce (Taakgroep Verkeer and Vervoer). The empirical model parameters were updated by comparing European type approval data with model predictions over the type approval cycle. A computer model developed by consultants Goudappel Coffeng and incorporating the FLEXSYT formulae calculates the vehicle emissions over the European type approval cycle. By comparing the modelling results with known type approval data, the model parameters could be empirically tweaked until they matched.
The update resulted in a large number of parameters being updated and a better estimate of vehicle emissions. The report describes the procedure adopted and reviews the model formulae.