Brain Jenkins @ RAND is always sensible and this short article reviews the current furore, 'Vehicular Terrorism: Weighting the Benefits and Worth, of Prevention.

A "taster":
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?
Link:https://www.rand.org/blog/2017/09/ve...and-worth.html