Estimation of Average Lifetime Vehicle Miles of Travel

During the September 23, 2004 Board hearing on the proposed AB 1493 regulation, a representative of Sierra Research, Inc. (SRI) commented that the Air Resources Board (ARB) staff had overestimated the miles traveled (VMT) in a vehicle’s average lifetime. The assertion was that this had in turn resulted in an overestimation of lifetime fuel savings and an underestimation of the payback period for vehicle owners. Overnight, the ARB staff performed a preliminary evaluation of the SRI written testimony, and acknowledged the following day that there appeared to be merit in the comment. Staff also stated that further evaluation of this issue was needed, including an assessment of the impact on mobile air conditioning credits which use VMT as an input. However, staff also showed that use of the lower estimate of lifetime VMT provided by SRI would not substantially affect operating cost savings or the payback period. The Board left open the possibility of modifying the method and the VMT estimate as a 15-day change, following further review.