for a mass-market vehicle with relatively long driving range on battery power alone (e.g., 40 miles or more) will require development of a low-cost, lightweight battery that can store the needed electricity and last for 10 years or more (Box 4.2).
Battery-electric vehicles. Successful development and deployment of PHEVs using advanced battery technology might lead to a battery suitable for BEVs (see Box 4.2). Although several models of BEVs are being introduced into the market today in low volumes, in the foreseeable future the only commercially viable BEVs may be small cars with modest performance expectations, such as “city BEVs.”
Hydrogen fuel-cell vehicles. Several scientific, engineering, and business challenges must be met before hydrogen FCVs can be successfully commercialized.21 The principal challenges are to increase the durability and lower the costs of fuel cells, achieve cost-effective storage of hydrogen in fueling stations and on board vehicles, and deploy a hydrogen supply and fueling infrastructure with low greenhouse gas emissions. These vehicles offer tremendous potential for reductions in oil imports and CO2 emissions in the long term (beyond 2035) but little opportunity for impact before 2020 because of the time required to address the technical and cost challenges and, subsequently, to achieve high-volume production.
Transmission Improvements in Light-Duty Vehicles
Automatic-transmission efficiency is likely to improve in the near term to midterm through increasing the number of gears and reducing losses in bearings, gears, sealing elements, and hydraulic systems. Seven- and eight-speed transmissions may become standard in the midterm. A continuously variable transmission (CVT) would in principle allow an engine to operate near its maximum efficiency, but its estimated actual efficiency improvement is lower than that expected for six- or seven-speed transmissions.