On residential streets, engineers attempt to control car speeds by installing traffic-calming devices . You probably know all about the venerable speed bump , but these days you’re more likely to drive over the lower and wider speed hump or the even wider speed table . Many people refer to these generally as sleeping policemen , a richly evocative, perhaps even poetic locution.

In 1861, when the few steam-powered automobiles around were known as road locomotives (or light locomotives), the British Parliament established the world’s first speed limit of 10 miles per hour (16 kilometers per hour). In 1865 a revised law slashed it to 4 mph in the country and 2 mph in towns and villages. Apparently alarmed by even these modest speeds, Parliament also decreed the world’s first traffic-­calming devices: each vehicle had to be preceded by a person walking 60 yards (about 55 meters) ahead and waving a red flag to warn others of the vehicle’s approach.

The world has seemed like a too-fast place ever since, and today’s traffic engineers spend much of their time getting people to slow down. Along the way they’ve developed a remarkable lingo.

One traffic-calming technology popular of late is the neckdown (also called a bulbout ), which is a curb that extends into the street on both sides of an intersection; narrowing the intersection forces cars to slow down. A similar idea is the chicane , an S-shaped curve that creates curb extensions drivers must negotiate. Speed bumps, humps, and tables fall under the category of vertical deflection , while neckdowns and chicanes are horizontal deflections .