New research suggests people drive more after transit is targeted, even though the choice actually elevates their safety risk.

On Friday, convicted terrorist Adis Medunjanin was sentenced to life in prison for plotting an attack on the New York City subway system several years back. Public transit has been the target of a number of similar efforts in the post-9/11 era: Madrid trains in 2004, London subway and buses in 2005, the Moscow metro in 2010. Fortunately, in the case of Medunjanin and his cohorts, law enforcement spoiled the plan before its execution.

Society doesn't need any additional incentive to prevent a terror attack beyond avoiding the tragedy itself. When the focus of such attacks is public transit, however, stopping them doesn't just save the lives directly at stake. It may also save road fatalities that occur in the aftermath as people shift back to their cars despite the higher general risk of a traffic accident, according to recent research.

An Israeli research team led by Wafa Elias recently surveyed hundreds of residents of Jerusalem and Haifa to see how their travel behavior changed in response to terror attacks that targeted public buses in those cities. Transit attacks are all too common in each city, going all the way back to 1948, resulting in hundreds of deaths and injuries. Yet even in 2002, when about 200 people were killed by terrorism in the deadliest year on record in Israel, road fatalities were roughly three times higher.

In an upcoming issue of Transport Policy, Elias and colleagues report a few general results from their questionnaires. They found that fear of a terror attack was similar in the two cities, even though Jerusalem is targeted more often. In Haifa, about a third of survey respondents indicated that they had stopped riding the bus for a period after a transit terror attack; in Jerusalem, the figure was close to 25 percent. More people said they would do so, in the future, if an attack targeted their regular bus line: 60 percent in Haifa, and 52 percent in Jerusalem.

In both cities, people said their fear of being involved in a car crash was greater than that of being in a terror attack — the proper response, at least as far as the statistics are concerned. Still, more than half of survey respondents said they drove when they stopped riding the bus after attacks, with another third saying they took taxis. Only about 11 percent switched to walking or bike-riding. This reaction suggested to Elias and colleagues that "an undesired shift" to private car use occurred after a transit attack, creating the potential for additional deaths:

People are aware that the risk of road crashes is higher than the risk of terrorist attacks. Although this fact accords with the reality even in a country like Israel, where there are far more fatalities from road crashes than from terrorist attacks, people’s behavior may be affected by the threat of a terrorist attack despite its low probability of occurrence.

Another result from the survey, which comes as no surprise, is that people who had access to a car were much more likely than others to refrain from using the bus in the event of a transit attack. That finding accords with another recent study of post-terrorism travel behavior, this one set for publication in an upcoming issue of Psychological Science. German researchers Wolfgang Gaissmaier and Gerd Gigerenzer report that "driving opportunity" was a substantial predictor of increased road fatalities in the aftermath of 9/11.

Gaissmaier and Gigerenzer looked at car crash data from October to December of 2001, and compared that to similar data from the previous five years. The researchers looked at changes across the country in traffic fatalities, miles driven, and "driving opportunity" — defined as major highway mileage per capita. They also considered proximity to New York City, as previous research suggested that road fatalities increased in areas near the attacks but not the rest of the country.

Contrary to that work, Gaissmaier and Gigerenzer found that traffic fatalities rose for all states immediately after 9/11, on average, despite a general decrease in fatalities during the previous five years. That increase was strongly tied to driving mileage: states averaged a monthly increase of 27 miles after the attacks, which far exceeded the rate from previous years. Nearness to New York was a slight indicator of driving mileage — but "driving opportunity," as measured by per capita highway mileage, was a much stronger one.

The behavioral moral of the recent work is that psychological fear accounts for only some of the indirect damage caused by a terror attack. Environmental factors, like having access to a car or more roads, can enable that outcome. Even understanding all this and knowing the numbers, a desire to drive after a transit (or plane) attack — a desire to retain some semblance of control — is completely reasonable. Far better to prevent the attacks in the first place, and remove any need to weigh science against instincts.

Top image: dotshock/

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