Speed Bumps And Speed Humps

Speed Bumps and Humps are included in the category that includes all traffic-calming devices raised above pavement level.  Drivers have no other choice than to slow down when they cross these devices or suffer an uncomfortable KER-BUMP or (KER-BUMP-KER-BUMP), running the risk of spilled coffee and a severe jolt to their tailbones.  Although people often gripe about the inconvenience of having to slow down for these devices, they don’t have much choice. Their effectiveness at slowing traffic cannot be disputed. They are sometimes referred to as “Silent Policemen.”

Included in this category are:
• Speed bumps.
• Speed humps.
• Raised crosswalks.
• Raised intersections.

Speed Bumps
A speed bump is a raised area in the roadway pavement surface extending transversely across the travel way, generally with a height of 3 to 6 inches and a length of 1 to 3 feet.

Speed Bump Design Considerations:
• Most effective if used in a series at 300- to 500- foot spacing.
• Typically used on private property for speed control – parking lots, apartment complexes, private streets, and driveways.
• Speed bumps are not conducive to bicycle travel, so they should be used carefully.

Speed Humps
A speed hump (or “road hump”) is a raised area in the roadway pavement surface extending transversely across the roadway. Speed humps normally have a minimum height of 3 to 4 inches and a travel length of approximately 12 feet, although these dimensions may vary. In some cases, the speed hump may raise the roadway surface to the height of the adjacent curb for a short distance. The humps can be round or flat-topped.

The flat-topped configuration is sometimes called a “speed table.” Humps can either extend the full width of the road, curb-to-curb, or be cut back at the sides to allow bicycles to pass and facilitate drainage.

Speed Hump Design Considerations:
• If mid-block pedestrian crossings exist or are planned, they can be coordinated with speed hump installation since vehicle speeds will be lowest at the hump to negotiate ramps or curbs between the sidewalk and the street.
• The hump must be visible at night.
• Speed humps should be located to avoid conflict with underground utility access to boxes, vaults, and sewers.
• Speed humps should not be constructed at driveway locations.
• Speed humps may be constructed on streets without curbs, but steps should be taken to prevent circumnavigation around the humps in these situations.
• Adequate signing and marking of each speed hump is essential to warn roadway users of the hump’s presence and guide their subsequent movements.
• Speed humps should not be installed in street sections where transit vehicles must transition between the travel lane and curbside stop. To the extent possible, speed humps should be located to ensure that transit vehicles can traverse the hump perpendicularly.
• A single hump acts as only a point speed control. To reduce speeds along an extended section of street, a series of humps is usually needed. Typically, speed humps are spaced at between 300 and 600 feet apart.

Speed Hump Real Life Example:
Bellevue, Washington has installed speed humps in residential neighborhoods (labeled as speed “bumps” below, although broader than the typical speed bump). The City uses a 12-foot-wide hump, 3 inches high at the center.  The design allows for little or no discomfort at speeds of 15 to 25 mph, but will cause discomfort at higher speeds. The humps are marked clearly, distinguishing them from crosswalks. White reflectors enhance nighttime visibility. Bellevue found that the speed humps reduced traffic speeds and volumes. The humps, in general, received strong public support, and residents favored their permanent  installation.

The following concerns were raised regarding the speed hump installation:

• Concern about restricted access and increased response time for emergency vehicles. The Bellevue Fire Department asked that the humps be installed on primary emergency access routes.
• Concern about aesthetics of signing and markings at the traffic humps. Residents raising the concerns, however, felt that the speed reductions compensated for the appearance of the humps.
• Concern about the effectiveness of the humps in reducing motor vehicle speeds along the length of a street, not at just two or three points. The distance between speed humps was found to
have an impact on traffic speeds. The City found that maximum spacing should be approximately
500 feet.

The Bellevue Department of Public Works concluded that speed humps were effective speed-control measures on residential streets and recommended their use be continued.

Next… Raised Crosswalks

The City of Austin, Tx has an excellent FAQ section about Speed Humps.

I’ve reproduced some of that faq here in this post but you really should visit this page where the original post occurs to get the full list of speed hump Frequently Asked Questions that they’ve posted.

These frequently asked questions about speed humps are a great resource to have at your fingertips if you are responsible for designing or specifying speed humps or even if you are considering speed humps for your own project.

Q. - Why do we have speed humps?

A. - Speeding on residential streets is a common complaint of concerned citizens. Although enforcement of speed limits by police departments is an effective means of reducing speeds, limited resources do not allow such enforcement on a regular and permanent basis. Research has shown that speed humps are an effective approach to slowing down traffic on residential streets.

Q. - What is a speed hump and how is it different from a speed bump?

A. - A speed hump is a gradual rise and fall of the pavement surface along the roadway extending across the pavement width. Generally, speed humps used on residential streets are 12 to 22 feet long with a maximum height of 3 to 4 inches. Speed “humps” are different from speed “bumps”, which are seen in many private parking lots.

A speed bump is abrupt, having a height of 3 to 4 inches over a length of 1 to 3 feet. Speed bumps cause most vehicles to slow down to almost a stop to go over it. Speed humps, on the other hand, are designed so most vehicles can go over them at 20 mph without causing driver discomfort.

Q. - How are speed humps effective in controlling speeds?

A. - Speed humps cause a gentle vehicle rocking motion that causes driver discomfort, thus resulting in most vehicles slowing down to 20 mph at each hump. Depending upon street geometry, speed humps are placed every 200 to 600 feet. The presence of speed humps causes drivers to slow down at the humps and in between properly spaced successive humps. Speed humps have the advantage of being self-enforcing. They are sometimes referred to as “sleeping police officers”.

Q. - What will happen if I go over speed humps at high speeds?

A. - At high speeds a speed hump can cause significant driver discomfort. At such speeds it can act as a bump and jolt the vehicle’s suspension and its occupants or cargo.

Q. - Do speed humps reduce cut-through traffic?

A. - The primary purpose of speed humps is to reduce the speeds of vehicles traveling along a roadway. Traffic diversion due to speed humps is a side effect which may or may not result. A possible disadvantage of speed humps is that motorists may avoid the speed humps by using other nearby streets in the area.

Q. - How is a driver warned of the presence of speed humps?

A. - On any street with speed humps, warning signs such as “Road Humps Ahead” are placed before the beginning of each series of humps. These signs also indicate the speed at which drivers are advised to travel over the hump. To be properly visible, the speed hump is marked with diagonal white stripes.

Q. - Can speed humps be placed on any street?

A. - Speed humps are placed only on residential streets with not more than two lanes and with a speed limit of 30 mph or less. For safety reasons, speed humps are not installed within sections which are curved or where the street slopes uphill/downhill.

Speed humps are not typically installed on streets where emergency facilities are located. The Department of Public Works and Transportation communicates with the Austin Fire Department and Emergency Medical Services to ensure that the speed humps will not greatly impact their services. Increases in response time of approximately 2-10 seconds per hump may exist with the installation of speed humps.

This is not by any means a comprehensive list of FAQ’s about speed humps but it certainly covers the basic questions asked about speed humps.  The answers too are as related to the public works division of a local US city government but for the most part these answers to frequently asked questions about speed humps can aid in understanding the issues involved with speed humps.