Cars have emerged as a preferred "weapon of choice" for terrorists, former NYPD Commissioner Bill Bratton told CNBC on Friday.
"It's low cost, low tech, very high impact and it follows the al-Qaeda and ISIS instructions to use guns, bullets, bombs and cars," Bratton said on "Squawk Box."
A manhunt is underway in Spain as police search for those responsible for a series of terror attacks, which killed at least 14 people and injured more than 100 others. The Islamic State group later claimed responsibilities for the attacks.
Spanish officials are looking for the driver of a van that plowed into pedestrians on Barcelona's busiest boulevard late Thursday. Two people were arrested but the van driver, who fled on foot, remained at large.
Early Friday morning, police killed five suspects engaged in an attack that injured six people in a seaside resort town and that the government for Spain's Catalonia region said was connected to the Barcelona killings.
Bratton said he and other security experts have discussed the impact of using vehicles and they have become increasingly concerned about coordinated attacks.
On Saturday, a car plowed into a crowd of people protesting a white nationalist rally in Charlottesville, Virginia, killing one person.
Bratton said he expects more attacks with vehicles.
"It follows a pattern. Attack with a car. Get out of the car and attack with guns, knives or in this case possibly suicide vest," he said. "It is, unfortunately, the new normal that we're going to have to start facing more frequently."
Media outlets in Europe said the suspected five terrorists were wearing fake suicide belts.
Bratton said the best defense countries have against these kinds of attack is intelligence.
"You can prevent a number of them by the monitoring social media, through the various intelligence entities that are out there," he said.
Many of the attackers as of late could be characterized as "lone wolf" who might be inspired by or enable by ISIS, Bratton said. "But are not being directed by them," he said.
—The Associated Press contributed to this report.