Testing energy and emissions assessment models: a highway case study in virtual reality

The estimation of pollutants from road transport systems is examined, by comparing emission factors (EFs) calculated with static and dynamic methods. Information technology is used to test currently operational assessment models in the European Union. The negligibility of the effects of variation in speed is questioned: acceleration/deceleration imply use/dissipation of energy, and directly affect pollutants release. An investigation based on drive simulation is conducted, proposing increasing traffic flow conditions. Two scenarios are simulated: an existing highway before and after major modernisation works. Benefits and detriments of its renovation are also examined. Results are processed through recent European Environment Agency models and a system that continuously computes the operations of an engine. The correlation found between average speed and EFs is not representative. Instead, a good correlation is observed between increases in speed variation and increases of EFs. Synthetic parameters are proposed to support the analysis, based on intensity and duration of acceleration/deceleration events. EFs are substantially lower if calculated through the static models. The assumption that the effects of speed variation can be neglected is rejected: driving cycles due to traffic flow conditions are identified as crucial for realistically evaluating emissions. A need is detected to formulate correcting parameters.