A speed hump (also called a road hump or undulation, and in Ireland called a speed ramp) is a rounded 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, circular, and sinusoidal.
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.
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 bumps
, 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.
Speed humps are constructed of asphalt
, or rubber
. 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 snowplows
. In addition, unlike concrete and asphalt, which necessitate frequent and high cost replacement, rubber products are longer lasting and thus more cost-efficient.
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 up to 10 seconds for ambulances
with patients on-board. Speed humps are thus usually not placed on primary response routes. Speed cushions
may be placed on these routes instead.
Occasionally, there is an increase in traffic noise from braking and acceleration 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, and SUVs are less affected by speed humps, and may not have to slow down as dramatically.
- Speed tables are longer than speed humps with a flat section in the middle. Cars are slowed less compared to speed humps.
- Speed cushions are a series of three humps that are ideal for use on streets when emergency vehicle response time is a concern.
- Speed bumps are significantly smaller than speed humps and used in areas where speed must be slowed nearly to a halt.