Speed hump

# Speed hump

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Encyclopedia

A speed hump is a rounded traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

device used to reduce vehicle speed and volume on residential streets. Humps are placed across the road to slow traffic and are often installed in a series of several humps in order to prevent cars from speeding before and after the hump. Common speed hump shapes are parabolic
Parabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...

, circular, and sinusoidal
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...

.

Generally, speed humps are 12 to 14 feet (3.7 to 4.25 m) in length and span the width of the road. The height of humps ranges from 3 to 4 inches (7.5 to 10 cm). The length and height of the speed humps determine the speed at which traffic will travel over the devices. Shorter lengths and greater heights slow cars most drastically. When placed in a series 350–550 feet (100–170 m) apart, humps will reduce 85 percentile speeds by 8–10 mph (13–15 km/h).

A warning sign notifies motorists before humps. Humps generally have pavement markings to enhance visibility and a taper edge near the curb to allow a gap for drainage.

Speed humps are used in locations where very low speeds are desired and reasonable. Speed humps are typically placed on residential roads and are not used on major roads, bus routes, or primary emergency response routes. Placement is generally mid-block between intersections.

## Results

Typical speeds resulting from speed humps are 10–20 mph (15–30 km/h). Studies show an average 18% reduction in traffic volume and an average 13% reduction in collisions.

## Comparison to speed bumps

While similar to speed bump
Speed bump
A speed bump is a speed-reducing feature of road design to slow traffic or reduce through traffic, via...

s, humps are less aggressive than speed bumps at low speeds and are used on actual streets, as opposed to bumps which are primarily placed in parking lots. While speed bumps generally slow cars to 5 – 10 mph (8 – 15 km/h), humps slow cars to 10 – 20 mph (15 – 30 km/h). The narrow nature of speed bumps often allows vehicles to pass over them at high speed while only perturbing the wheels and suspension, hardly affecting the vehicle cab and its occupants. The relatively long slopes of speed humps gradually accelerate the entire vehicle in vertical direction, causing the perturbation of the cab to become progressively more severe at higher speeds.

## Composition

Speed humps are constructed of asphalt
Asphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...

, concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, or rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

. While traditionally most humps were constructed of asphalt or concrete, rubber is becoming increasingly common in some regions for several reasons. Asphalt and concrete can be difficult to construct precisely while rubber products are pre-shaped to standardized sizes and thus consistently meet industry standards. An additional advantage is ease of installation, which is particularly beneficial when a city wants to test streets before deciding where to keep the devices. The simple installation process also allows for relocation during the winter when snow is a concern, which prevents damage to the humps by snowplow
Snowplow
A snowplow is a device intended for mounting on a vehicle, used for removing snow and ice from outdoor surfaces, typically those serving transportation purposes...

s. In addition, unlike concrete and asphalt, which necessitate frequent and high cost replacement, rubber products are longer lasting and thus more cost-efficient.

## Criticisms

One criticism of speed humps is their effect on emergency vehicles. Response time is slowed by 3–5 seconds per hump for fire trucks and fire engines
Fire apparatus
A fire apparatus, fire engine, fire truck, or fire appliance is a vehicle designed to assist in fighting fires by transporting firefighters to the scene and providing them with access to the fire, along with water or other equipment...

and up to 10 seconds for ambulances with patients on-board. Speed humps are thus usually not placed on primary response routes. Speed cushion
Speed cushion
Speed cushions are traffic calming devices designed as several small speed humps installed across the width of the road with spaces between them. They are generally installed in a series across a roadway resembling a split speed hump. The design of speed cushions forces cars to slow down as they...

s may be placed on these routes instead.

Occasionally, there is an increase in traffic noise from braking and acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

of vehicles on streets with speed humps, particularly from buses and trucks. Other effects include increased vehicle fuel consumption and emissions – as most fuel injection systems in modern internal combustion engines operate in open-loop mode (fuel rich) when accelerating – as well as increased wear and tear on brakes, engine and suspension components.

Damage caused by snow plows during the winter months is an additional concern.

Heavy sedans, trucks
Pickup truck
A pickup truck is a light motor vehicle with an open-top rear cargo area .-Definition:...

, and SUV
Sport utility vehicle
A sport utility vehicle is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. It is usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle. Not all four-wheel...

s are less affected by speed humps, and may not have to slow down as dramatically.

Thin cuts are sometimes placed in the middle of a hump in order to allow bicycle
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

traffic to pass through. However, forcing cyclists to take a particular line on the road compromises their ability to position themselves safely according to the other traffic on the road at the time.

## Similar devices

• Speed table
Speed table
A speed table is a traffic calming device designed as a long speed hump with a flat section in the middle. Speed tables are generally long enough for the entire wheelbase of a passenger car to rest on top. The long, flat design allows cars to pass without slowing as significantly as with speed...

s are longer than speed humps with a flat section in the middle. Cars are slowed less compared to speed humps.
• Speed cushion
Speed cushion
Speed cushions are traffic calming devices designed as several small speed humps installed across the width of the road with spaces between them. They are generally installed in a series across a roadway resembling a split speed hump. The design of speed cushions forces cars to slow down as they...

s are a series of three humps that are ideal for use on streets when emergency vehicle response time is a concern.
• Speed bump
Speed bump
A speed bump is a speed-reducing feature of road design to slow traffic or reduce through traffic, via...

s are significantly smaller than speed humps and used in areas where speed must be slowed nearly to a halt.