Speed bumps (also called traffic thresholds, speed breakers or sleeping policemen) are a class of traffic calming devices that use vertical deflection to slow motor-vehicle traffic in order to improve safety conditions. Variations include the speed hump, speed cushion, and speed table.

The use of vertical deflection devices is widespread around the world, and they are most commonly used to enforce a speed limit under 40 km/h (25 mph).

Although speed bumps are effective in keeping vehicle speeds down, their use is sometimes controversial—as they can increase traffic noise, may damage vehicles if traversed at too great a speed (despite that being the point), and slow emergency vehicles. Poorly-designed speed bumps that stand too tall or with too-sharp an angle can be disruptive for drivers, and may be difficult to navigate for vehicles with low ground clearance, even at very low speeds. Many sports cars have this problem with such speed bumps. Speed bumps can also pose serious hazards to motorcyclists and bicyclists if they are not clearly visible, though in some cases a small cut across the bump allows those vehicles to traverse without impediment.

Each of these devices can be made from a variety of materials, including asphalt, concrete, recycled plastic, metal, or vulcanized rubber. Several trade-offs must be made when selecting the material for a new speed cushion. Traditionally most vertical deflection devices have been constructed of asphalt or concrete. Due to the rigidity and durability of these materials, they have more permanence and are more effective at slowing traffic. However, they can be difficult to shape and form into consistent forms and precise dimensions.

Rubber products are pre-shaped to standard sizes to meet industry standards. Preformed rubber products are typically bolted down, making them easier to install or remove. Temporary bolt-down installations can be ideal for planners in testing the use and positioning of speed bumps before implementing them in a larger project. Bolt-down products can also be removed or relocated during winter snow periods—where speed bumps are easily concealed and may be damaged by snowplows.

On June 7, 1906, The New York Times reported on an early implementation of what might be considered speed bumps in Chatham, New Jersey, which planned to raise its crosswalks five inches (13 cm) above the road level: "This scheme of stopping automobile speeding has been discussed by different municipalities, but Chatham is the first place to put it in practice". The average automobile's top speed at the time was around 50 km/h (30 mph), but braking was poor by modern standards.^{[citation needed]}

Arthur Compton was a physicist and winner of the 1927 Nobel Prize in Physics for his discoveries resulting in major changes in electromagnetic theory. He is commonly known for his work on the Compton effect with X-rays. He also invented what he called "traffic control bumps", the basic design for the speed hump, in 1953. Compton began designs on the speed bump after noticing the speed at which motorists passed Brookings Hall at Washington University in St. Louis, Missouri, where he was chancellor.

The British Transport and Road Research Laboratory published a comprehensive report in 1973 examining vehicle behavior for a large variety of different bump geometries. At the time speed humps were not permitted on public roads but had been installed on private roads.