Tidswell, James

Accounting for excess cold emissions in traffic assignment models with emission objectives

James Tidswell, Andrea Raith, and Anthony Downward

Department of Engineering Science, University of Auckland

There has been increased awareness of greenhouse gases and associated climate change, where the transport sector makes a significant contribution to greenhouse gases via vehicle emissions. This has provoked interest in estimating vehicle emissions through the use of traffic models, such as in the Vehicle Routing Problem and the Traffic Assignment problem. Emissions models used within these traffic models generally consider the ‘hot’ emissions, which are the emissions produced while the vehicle engine is at operating temperature, and are a function of average speed. In this presentation we consider accounting for the initial portion of a vehicle user’s trip where the vehicle engine starts at below operating temperature, producing excess ‘cold’ emissions, which are generally a function of trip length. We examine two methods of modelling cold emissions and incorporate them into a Traffic Assignment model, addressing the path-dependent shortest path problem that arises with path-length-dependent emissions costs on arcs, and propose an algorithm to identify the shortest path in a network with path-dependent arc costs. Incorporating this algorithm into the traffic assignment model allows the evaluation of solutions to the traffic assignment problem with path-dependent objectives.

This presentation is eligible for the ORSNZ Young Practitioners Prize.