You can impede manned vehicles with traffic cones in exactly the same way. Randomly put them on roads, and people will stop, causing traffic jams. Throw them under the wheels of moving cars, and people will crash and likely die.
Allowing people to drive 2-tonne death traps around dense urban areas seems like a bigger mistake.
Allowing people to drive 2-tonne death traps around dense urban areas seems like a bigger mistake.