Preventing people from using vehicles as deadly weapons is a difficult task for law enforcement officials, experts say.

Cars, trucks and vans have been used to ram people more than a dozen times around the world in recent years, often with deadly results similar to those in northern Toronto on Monday.

Federal Public Safety Minister Ralph Goodale said Monday night what happened does not appear to be connected to national security, but he called the incident a 鈥渉orrific attack.鈥�

Not all recent vehicle attacks have been linked to terror groups, says Candyce Kelshall, an adjunct professor with the terrorism, risk and security studies program at Simon Fraser University in Burnaby, B.C.

She says there have been at least three incidents in Germany in recent years where people have driven cars into groups or buildings, but did not have any connection with Islamic State militants or other terrorist organizations.

Regardless of the motive, it鈥檚 tough to stop someone from using a vehicle to kill, Kelshall says.

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鈥淵ou can鈥檛 stop people driving cars or walking on streets,鈥� she says. 鈥淚t鈥檚 a difficult to thing to police.鈥�

Vehicles are a popular weapon because they鈥檙e accessible, says Alex Wilner, an assistant professor with Carleton University鈥檚 Norman Paterson school of international affairs in Ottawa.

鈥淚t鈥檚 deadly, it鈥檚 easy and it鈥檚 cheap. So, if you put the math together, it doesn鈥檛 take a lot to kill people,鈥� he says.

Cities are increasingly looking for ways to place barriers between vehicles and pedestrians, Wilner says.

In some places, garbage and fire trucks are being put in place at entrances to festivals or markets, he adds.

Similar safety measures were in effect in Toronto on Monday night, with streets closed near the Air Canada Centre where the Maple Leafs were playing an NHL playoff game.

Wilner says several vehicles used in recent attacks have been rentals and there may be some appetite for creating a registry to help prevent similar occurrences. What a registry or database would look like is unclear, he adds.

Mubin Shaikh, an expert on counterterrorism, says he thinks a no rental list would be a reactive measure that would have minimal impact.

If there are restrictions on rentals, people can still borrow or steal vehicles, he notes.

鈥淎 criminal will try to take whatever they can, however they can,鈥� he says.

鈥淲ill it deter the determined attacker? Probably not.鈥�

Shaikh, who is from Toronto, said he heard about Monday鈥檚 tragedy after landing at an air force base in Germany where he was scheduled to give a briefing on attacks using vehicles.

鈥淯nfortunately, this is the reality in which we live nowadays,鈥� he said, adding that he鈥檚 become hyper-vigilant when walking down the street and is constantly looking for cement planters or pillars that he could hide behind if a vehicle jumps the curb.

鈥淎t the end of the day, it鈥檚 impossible (to prevent). We live in an open society and vehicles are in our proximity all the time. That鈥檚 normal city life.鈥�

Gemma Karstens-Smith, The Canadian Press

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