The United States has made massive investments in building and operating transportation facilities and services, but increased passenger travel and global trade are pushing the transportation sector to its limits, according to Critical Issues in Transportation, the latest document in a series on the subject by the National Academies’ Transportation Research Board (TRB).

The transportation system is facing a host of challenges that could affect the US economy and citizens’ quality of life, said TRB’s executive committee, which authored the document. Among the issues identified are the transportation sector’s vulnerability to terrorist strikes and natural disasters; inadequate revenues to maintain transportation systems and increase their capacity; aging infrastructure; over-reliance on fossil fuels; and lack of political will to crack down on irresponsible driving.

‘The destruction caused by Hurricane Katrina demonstrated the vital importance of transportation in responding to natural disasters, and the massive traffic jams during the evacuation from Hurricane Rita showed what happens when the system does not perform as expected,’ said John R. Njord, chair of TRB’s executive committee. ‘The urgent need to address critical issues facing transportation has never been greater.’

One key issue is congestion; all modes of transportation are straining to meet demand. New roads will be needed in the rapidly growing metropolitan areas that are expected to absorb tens of millions of new inhabitants in the next three or four decades. Other solutions may include new or modified user fees and better travel information for drivers. Similarly, railroads, airports, ports, and transit systems will require greater capacity as the US population and economy grow.

Congestion significantly impacts businesses, especially those shipping freight through ports and across the US borders with Mexico and Canada. Longer transport times increase costs, and lack of reliable delivery compels firms to hold onto inventory for longer or add extra time for shipments. Also, sharp growth in global trade—particularly with Asia—is placing unprecedented demands on freight systems. Over the next 20 years, West Coast ports may be unable to handle growth in Asian trade, the committee said.

Another issue highlighted in the document is transportation security. Efforts to improve security still face many obstacles, the committee noted. Although initiatives have been deployed by the US Department of Homeland Security—including increased passenger and baggage screening at airports and security checks for drivers of trucks with hazardous cargo—the efficiency and effectiveness of screening needs to be improved without sacrificing citizens’ privacy, the committee said. The question of who should pay for the added costs of security also must be resolved.

The transportation sector relies almost exclusively on petroleum-derived fuels, adding to the country’s dependence on foreign sources of energy. To address this issue, alternative energy sources have been introduced—such as hydrogen and biodiesel—but additional research and development is required before a strong substitute will emerge. The transition to any alternative will take decades, the committee added.

In the meantime, the effects of petroleum-based fuels on the environment and human health need to be reduced, the committee said. Many areas of the country have yet to attain existing federal clean air standards, and many more will struggle to meet new standards for fine particulate matter released by diesel engines.

Another critical issue is the lack of funding. Federal, state, and local agencies do not have adequate revenues to maintain the aging transportation infrastructure and increase its capacity. For highways and air transportation, revenue from users is not keeping pace with increased demand. Also, Amtrak is in the midst of a major financial crisis, and public transit systems are facing considerable financial problems despite sharp increases in ridership in r