This report summarizes a review of efficiency and cost assumptions for road transport vehicles from 2010 to 2050 conducted for the Committee on Climate Change. The review developed datasets for fuel efficiency and capital costs for 9 vehicle categories and 13 powertrain technologies. It found that conventional powertrains have the greatest potential efficiency improvement but remain less efficient than electrified options. Capital costs of alternatives are expected to narrow substantially by 2030 and may be lower than diesel vehicles by 2030 when fuel costs are considered. The review assessed the validity of the CCC's assumption of no efficiency improvement without policy and found this assumption reasonable for cars but not for other vehicles which may see gradual annual efficiency gains.