The calculation of emission factors is conducted by TNO-Automotive in Delft. This institution has conducted an extensive measurement programme for the Ministry of Housing, Spatial Planning and the Environment since 1987, taking samples to check whether motor vehicles meet the requirements with respect to emissions of polluting substances. TNO measures the effects of, for instance, low outside temperatures, emission levels of older vehicles and air conditioners.
In 2007, the VERSIT model was introduced at TNO to calculate emission factors of road vehicles. Differences with the prevailing methods are considerable:
- The new calculation model uses a different calculation method. Until recently, emission factors were estimated on the basis of the available data and expert judgement. The VERSIT plus LD (LD stands for light duty: motorcars and vans) uses statistical models based on a huge emission database and covers a much larger variety of vehicle types.
- Traffic situations are described more elaborately and driving patterns monitored by TNO are taken into account.
- The current version of the model is based on the latest emission measurement programmes conducted by TNO. The emission factors used so far did not provide such information.
- The calculation modules in VERSIT plus HD (HD stands for Heavy Duty: heavy commercial vehicles) have been updated recently using new foreign data (emission maps) and comply with the latest views on vehicle parameters.