Terrorist are using cars as weapons. How can we protect ourselves?

Westminster Bridge by Katie Chan,
via Wikimedia Commons

In an alarming number of recent terror attacks, the assailants have made use of vehicles to ram or crush their victims. Recently, an attacker killed three people on Westminster Bridge in London by hitting them with a hired vehicle before getting out of the car and fatally stabbing a police officer. Last year on Bastille Day, an attacker drove a truck through celebrating crowds in Nice and killed eighty-four people. These attacks and others would indicate a disturbing trend even without reports the Daesh has recommended the use of vehicles to sympathizers aiming to commit lethal terror attacks.

Nice Bay by Fecchi, via Wikimedia Commons

Shortly after the derisively named "undies bomber" failed to blow up a plane bound for the United States with underwear soaked with explosives, American and international aviation authorities severely restricted the liquids they permitted passengers to carry on board. They had, of course, long forbidden passengers from bringing knives into the cabin of an airliner. Every time a terrorist organization attempts an assault against the civil aviation system, even if they fail, even if they fail in a risible manner, regulators take action. With several terror attacks committed using road vehicles, reports the Daesh has specifically committed to  this method of inflicting casualties, the call for road safety authorities to take some action would seem obvious.