substantial improvement in traffic flow. On major facilities, speeds of 40 km/hr (25 mph) or less imply that congestion is so heavy that minor interruptions can lead to complete breakdowns in flow. Under such conditions the probability of minor traffic accidents increases, and such incidents can cause long delays. Roughly half the delays are attributed to incidents that disrupt traffic flows (Schrank et al. 1993). Thus, maintaining a steady flow, even at modest speeds, can substantially improve traffic conditions.

Faster-moving traffic and more reliable traffic conditions would be valuable to commercial road users in congested metropolitan areas. A wide variety of commercial users depend on the road system. Although the large trucks delivering cargo to stores and factories come immediately to mind, commercial users also include panel trucks carrying package freight to stores and homes and light-duty vehicles driven by carpenters, electricians, plumbers, and delivery workers. Salespeople are also regular users of the road system, as are business people traveling between appointments or making trips to airports. Congestion causes immediate productivity losses to employers whose workers are stuck in traffic. Delays in the delivery of goods mean that physical assets are not being used efficiently. Increases in the transit time of cargo increase inventory costs. Although commercial users are among those highway users least able to shift to avoid congestion fees, it would appear that they are also among the users most likely to gain. Studies or analyses of the assumed benefits of congestion pricing to business activity and commercial transportation, however, have not been made for U.S. metropolitan areas.

Concern about meeting state and federal air quality standards is a prime motivator behind the renewed interest in congestion pricing. Despite considerable reductions in several types of emissions over the last 20 years, many metropolitan areas are still unable to meet air quality standards for ozone and carbon monoxide. Emissions from automobiles are major sources of these pollutants. Some 94 urban areas are currently out of compliance with federal standards for ozone (EPA 1993); the 1990 CAAA requires those areas classified with “moderate” or higher nonattainment (55 urban areas) to develop specific measures to reduce the emissions caused by automobiles. EPA has designated 42 areas as being in non-attainment for carbon monoxide.