To reduce speed on a street we can do a number of things:
Islands that project out from each side street, making it narrower and creating a zig-zag effect that slows cars down.
Chicanes are suitable for residential streets and some smaller roads but not thoroughfares or main roads.
Speed humps and platforms
A narrow mound of seal across a road that causes cars to judder as they drive over.
Most cars will slow down for these and they are suitable for residential streets but not thoroughfares or main roads.
Placing these in the middle of a road narrows the lanes and causes traffic to slow. These are suitable in a number of situations.
Flush median strips
Painted areas of road, usually painted in white with diagonal stripes. These also narrow the road, causing traffic to slow and are suitable for thoroughfares or main roads.
Partial road closures
Closing off the exit at one end (no exit roads) to prevent people from using it as a fast thoroughfares or main bypass street. This is suitable for some smaller roads.