Estimating the Energy Consumption Impact of Casual Carpooling

Some of the transport energy consumed during peak commuter periods is wasted through slow running in congested traffic. Strategies to increase average vehicle occupancy (and reduce vehicle counts and congestion) could be expected to be at the forefront of energy conservation policies. Casual carpooling (also called ‘slugging’) is a system of carpooling without pre-arrangement. It operates in three US cities, and has been suggested in New Zealand as a strategy for managing transportation challenges when oil prices rise. The State of Washington will pilot a formalized version of the system during 2010. The objective of the paper is to find out if casual carpooling saves energy, and if so how much. New models are developed for thinking about the issues and making estimates. Energy consumption by single occupant vehicles; casual carpool vehicles; and a mix of buses and single occupant vehicles; are estimated and compared. The paper concludes that energy could be saved by encouraging systems that emulate casual carpooling and suggests that policy should encourage development of carpooling without pre-arrangement as a mechanism for saving energy.