are likely to be influenced by changes in these service industries and by the design and repairability of the PNGV vehicle.

The adoption of alternative PNGV power plants that use fuels such as methanol, dimethyl ether or hydrogen would create immense demands on the entire fuel production, transportation, storage, and retail-distribution infrastructure. Significant new investments would be required both in the production and retail segments. Portions of existing facilities and equipment could become obsolete, resulting in the early writeoff of investments. The willingness of consumers to adapt to the use of alternative fuels will also have an important influence on the success of the PNGV program.

The highway infrastructure includes the highway system, the vehicle and its operator, and the services associated with vehicle operation. The operation of vehicles produces the undesirable consequences of property damage, human casualties, and environmentally harmful emissions. A number of significant issues relating to PNGV arise from highway infrastructure considerations.

Today's highway designs are predicated on existing interrelationships among the vehicles, the operators, the highway, and the operating environment and have evolved over a period of about 100 years. Any major change in the vehicle and its attributes requires an understanding of possible ramifications for existing relationships. Obvious examples include the compatibility of breakaway roadway sign supports and the crash characteristics of vehicles constructed with lightweight materials in support of occupant crash protection strategies. Similarly, new hazards from toxic substances, electrical discharges, and high momentum rotating devices will require special skills by emergency response personnel during crash rescue and when clearing and disposing of crash debris.

There is a large base of knowledge and experience from owning and operating current vehicles. Any major change in the vehicle dynamic response or vehicle-operator interaction will require adaption by vehicle operators. Changes in vehicle dynamic response, vehicle maintenance, safety precautions, and fuel handling procedures all could require behavior modifications that may impact the operator's acceptance of a PNGV-type vehicle.

The operating environment of the vehicle/highway system poses numerous issues to the PNGV. These issues include both regulated and unregulated emissions, road and vehicle noise, and highway runoff. Any changes that impact environmental quality need careful analysis. In reducing regulated highway emissions, due attention must be given to the total environmental impact, including in-use emissions and energy consumption in fuel production and distribution.