Intermittent Interruptions of Transportation Services

Intermittent Interruptions of Transportation Services

Natural disasters, accidents, labor disputes, terrorism, security breaches, and other unforeseeable incidents can result in major disruptions to the transportation system. Although a comprehensive account of these unpredictable interruptions has not been undertaken nor data compiled on them, numerous studies and other analyses have sought to evaluate the effects of individual events on the transportation system.

Terrorist attacks and security alerts have affected transportation services for decades. However, efforts to increase transportation security have grown markedly since the attacks of September 11, 2001. The short- and long-term effects of September 11 on transportation and ancillary services are still being assessed. In the short-term, airport enplanements and flight activity were substantially lower immediately after September 11 (figure 59). In fact, all flights scheduled for September 12 were canceled, and many other flights were canceled during the remainder of the month and the months that followed. Air passenger traffic has not fully recovered two years after the attacks, however other factors, such as an economic downturn, may also be part of the cause.

Vehicle accidents are a common cause of transportation delays. National estimates, based on model simulations, suggest that nearly 40 percent of nonrecurring delays on freeways and principal arterials are due to crashes. Weather, another unpredictable factor, accounts for 27 percent of highway delays. Relatively fewer delays resulted from road work-zones (24 percent) and vehicle breakdowns (11 percent) [1]. Although motor vehicle accidents are, by far, the most frequent type of transportation accident, other modes also experience major disruptions due to accidents. A freight train carrying hazardous materials derailed in a Baltimore tunnel in 2001 [2]. The resulting fire lasted several days and forced the city to close some highways and rail passages. Freight and passengers were delayed as trains were diverted hundreds of miles throughout the Middle Atlantic region.

The United States, because of its size and varied geography, is vulnerable to many types of natural disasters that can affect transportation. The flooding of the Mississippi River in 1993 shut down large portions of the inland waterway system, washed out rail track, damaged rail bridges, and closed an estimated 250 highway segments and bridges [3]. The following year, the Northridge earthquake had a major impact on the Los Angeles metropolitan area transportation system. Measuring 6.8 on the Richter scale, the earthquake knocked out four freeways, caused the collapse of parking structures, and ruptured numerous natural gas distribution lines [4, 5].

Disputes initiated by labor or business and other business adjustments can disrupt the passenger and freight transportation system. For example, a strike by San Francisco Bay Area Rapid Transit employees caused huge traffic jams on bridges and highways in 1997; a strike by United Parcel Service employees stalled shipments of goods later that year; and a labor lockout by terminal operators shut down west coast ports for 10 days in 2002 [6, 7]. A different type of business-related disruption caused problems on the Union Pacific Railroad in 1997. Following a merger with Southern Pacific Railroad in 1996, accidents and congestion overwhelmed the expanded railroad, resulting in federal intervention [6].


1. Chin, S.M., O. Franzese, D.L. Greene, H.L. Hwang, and R. Gibson. “Temporary Losses of Highway Capacity and Impacts on Performance,” Oak Ridge National Laboratory, May 2002.

2. National Transportation Safety Board, “Update on July 18, 2001 CSXT Derailment in Baltimore Tunnel,” press release, Dec. 4, 2002, available at, as of April 2003.

3. U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Statistics Annual Report 1994 (Washington, DC: 1994).

4. _____, Transportation Statistics Annual Report 1995 (Washington, DC: 1995).

5. _____, Journal of Transportation and Statistics: Special Issue on the Northridge Earthquake 1(2), May 1998.

6. _____, Transportation Statistics Annual Report 1998 (Washington, DC: 1998).

7. _____, U.S. International Trade and Freight Transportation Trends (Washington, DC: 2003).