A version of this commentary originally appeared in the opinion section of FoxNews.com.

The terrorist attack in Barcelona is the latest example of what has the makings of a chilling trend in modern terrorism. Airline hijackings came to define terrorism in the 1970s as did suicide bombings in the 1980s, and now the use of vehicles to mow down pedestrians is becoming increasingly commonplace. The style of attack has been given a name—vehicular terrorism—and it was employed in Spain in mid-August by a driver of a van who mowed down pedestrians, killing at least 14 and injuring scores of others.

This latest in a string of such attacks has added urgency to discussions of what can be done to prevent terrorists from using vehicles as weapons. In the lexicon of the security world, these ideas come under the heading of “hostile vehicle mitigation measures,” and they include a broad range of possibilities. Mitigation, not prevention, is the operative word here—cities are filled with pedestrians and vehicles, in some cases, separated by mere inches. Many of the measures would be disruptive and costly and could easily be circumvented, which leads to an uncomfortable question: Do they represent a good investment?

Ten Potential Mitigation Measures

Armed police: More armed police can be deployed to increase surveillance and respond more quickly to an event. However, the time between a moving car or truck suddenly veering into pedestrians and a street filled with casualties is a matter of seconds—rapid response is still good, but cannot prevent carnage.

Increased surveillance: Theoretically, algorithms could be developed to help rental companies identify out-of-the-ordinary rentals, much like airlines use similar methods to identify passengers meriting greater scrutiny. This could prompt crosschecking with existing databases. But it will not prevent terrorists from borrowing or stealing vehicles, or using their own.

Pedestrian barriers: The fences between sidewalks and the street that now prevent jaywalking or street crossings at dangerous intersections—can be strengthened and expanded. It complicates street parking, but parked cars are themselves a barrier.

Traffic obstructions: Bollards, or posts, can be installed (or trees grown) to prevent any vehicle that jumps the curb from traveling more than 20 or 30 feet on a sidewalk.

Slow down traffic: Speed bumps can be installed, slowing down and increasing traffic, and potentially impeding a terrorist armed with a vehicle.

Barriers at events: Trucks are now routinely parked to block streets hosting open-air markets. For instance, vehicle access is denied to the thousands gathered in New York's Times Square on New Year's Eve. Measures were in place to protect those watching the fireworks on Bastille Day in July 2016 in Nice, France, but a security failure may have allowed an unchecked cargo truck to enter the protected area—and 84 people died in the attack.

Protecting government buildings: The threat of terrorist truck bombs has already resulted in road closures and the installation of barriers around government buildings. These measures can be expanded.

Widening the security circle: On a more ambitious level, entire portions of cities can be surrounded by surveillance measures and physical barriers. During the IRA's terrorist campaign, “rings of steel” encircled downtown Belfast and later the financial district of London. Short of permanent measures, police can set up checkpoints and conduct random vehicle stops, as they do to detect drunken drivers or look for suspicious drivers and vehicles at airports.

Pedestrian walkways: More busy shopping streets and restaurant rows can be pedestrianized, already a popular trend.

Technological solutions: Various electronic means of remotely shutting down vehicles exist and could possibly be employed to prevent vehicular attacks. Looking ahead, autonomous vehicles could be programmed to preclude their use as weapons, although self-driving cars could be prone to hacking.

Putting Countermeasures in Perspective

More analysis is required to determine which of these barriers to vehicular terrorism would be more effective, identify other countermeasures and figure out what they would cost. But this does not preclude a discussion of whether the potential results merit the disruption and investment.

Worldwide since 2000, there have been approximately 40 deliberate vehicle attacks.

My recent search of public databases shows that worldwide since 2000, there have been approximately 40 deliberate vehicle attacks by terrorists, or in some cases, mentally unstable individuals. (There may be more, but none involving major casualties.) The identified attacks have resulted in a total of 167 deaths, an average of four per incident. Putting aside the statistical outlier in Nice, the average is two fatalities per attack—the median is one.

While relatively easy to carry out, vehicle attacks have not proved to be the most lethal terrorist tactic. And it is not clear that any of the suggested potential security measures would prevent a determined terrorist behind the wheel from driving a bit further to get roughly the same results.

In the United States, between 200 and 300 people are killed every year at railroad grade crossings. Another 6,000 pedestrians a year die after being struck by vehicles, a number suspected of increasing in part because drivers and pedestrians are paying more attention to their cellphones than to where they are going. In addition, drunken drivers are responsible for about 15 percent of pedestrian deaths.

This death toll is, of course, deplorable, but fatalities due to railroad crossings and drunken driving have not led to calls to redesign the urban landscape. A tiny fraction of the carnage, when caused by terrorists, however, creates alarm—and that changes the equation. Even a relatively small amount of violence, when it is random and theoretically appears to make every one of us a potential target, has enormous psychological power. Something must be done, whatever the costs or societal effects. In that sense, terrorism works.

Brian Michael Jenkins is a senior adviser to the president of the nonprofit, nonpartisan RAND Corporation and director of transportation security research at the Mineta Transportation Institute.

This commentary originally appeared on Fox News Channel on September 3, 2017. Commentary gives RAND researchers a platform to convey insights based on their professional expertise and often on their peer-reviewed research and analysis.