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 most fundamental traffic-calming goal is to reduce the speed of vehicular traffic . With the reduction of speed, the following important objectives can be realized:

1. Improved “feel” of the street.

This objective calls for increased community involvement in and “ownership” of the street. If people feel more comfortable on the street, they are more likely to walk or bicycle there and to engage in other street oriented activities with their neighbors. A key aspect of achieving this objective is reducing the perceived threat of danger from motor traffic.

2. Enhanced aesthetic values and a sense of nature.

Several traffic-calming techniques, such as street landscaping, pedestrian amenities, and reclamation of roadway areas can serve as community open space.  Not only do these techniques make the neighborhood more attractive, but they also break up long, uninterrupted street vistas conducive to speeding and convey the message that “this is a pedestrian place.”

3. Reduced crime.

It’s harder to make a speedy getaway if a fleeing felon has to deal with speed humps, woonerfs, and traffic circles. It’s harder to get away without being spotted if there are “eyes on the street” – if the street is a positive, community focus.

4. Equitable balance among transportation modes.

With reduced motorist speeds, safety is improved. Pedestrians and bicyclists have more time to detect and avoid motor vehicles. Traffic calming sends the message that “motor vehicles don’t exclusively
OWN the roadway” – that other modes have equal rights. Studies that evaluate traffic-calming improvements show increased levels of walking, bicycling, and transit use following installation.

5. Increased safety/decreased severity of injury in traffic crashes.

With reduced speeds comes a significant reduction in the number and severity of crashes involving motor vehicles. Traffic-calming facility evaluations uniformly show fewer crashes, fewer fatalities, and less severe injuries.

6. Improved air quality and noise levels.

Slower moving vehicles make less noise and, generally, emit fewer pollutants.

7. Decreased fuel consumption.

With more trips made by walking, bicycling, and transit, and with slower traffic speeds, fuel consumption reductions of 10 to 12 percent have been reported.

8. Continued accommodation of motor vehicle traffic.

An important objective is the continued accommodation of motor vehicle traffic. Although traffic calming shifts the balance among travel modes, this shift should not result in severely restricted traffic volumes or in shifting traffic problems from the traffic-calmed area to other streets.

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.

Traffic Calming? What is it?

According to our friends at the Instutute of Transportation Engineers:

Traffic Calming is the combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior and improve conditions for non-motorized street users.¹

Traffic calming goals include:

• increasing the quality of life;
• incorporating the preferences and requirements of the people using the area (e.g., working, playing, residing) along the street(s), or at intersection(s);
• creating safe and attractive streets;
• helping to reduce the negative effects of motor vehicles on the environment (e.g., pollution, sprawl); and
• promoting pedestrian, cycle and transit use.¹

Traffic calming objectives include:

• achieving slow speeds for motor vehicles,
• reducing collision frequency and severity,
• increasing the safety and the perception of safety for non-motorized users of the street(s),
• reducing the need for police enforcement,
• enhancing the street environment (e.g., street scaping),
• encouraging water infiltration into the ground,
• increasing access for all modes of transportation, and
• reducing cut-through motor vehicle traffic.

¹Lockwood, Ian. ITE Traffic Calming Definition. ITE Journal, July 1997, pg. 22.

This excellent article just about says it all.  It not only defines what traffic calming is it also provdes the objectives and goals of traffic calming devices.

As I am sure you can tell from this excerpt, the ITE traffic calming website is an excellent resource to use when you need information about speed bumps, speed humps, speed tables or any other type of traffic calming device.  So check it out!

Imagine New York City without cars…!

… and, Speed Bumps with gaps for Emergency Vehicles Only?

To me, both seem pretty hard to imagine.

But we might not have to have such vivid imaginations to actually see both happen in the near future thanks to New York’s first “Street Design Manual”.

According to the reputed “Architect’s Newspaper” the manual was well received by “… a large crowd of planners, engineers, and designers. Excitement ran high among both the speakers and the crowd, not just for the manual itself but for what it represents: New York’s determination to conceive of greener, more people-friendly streets, and an unprecedented inter-agency collaboration toward that end. “This is like the Woodstock of urbanism!” laughed Benepe.”

The article went onto say that the purpose of the Street Design Manual was “clearly committed to being in the vanguard of street design, venturing beyond the tried-and-true standards into more experimental waters.” “…That includes speed cushions (speed bumps with gaps that allow emergency vehicles to pass through at full speed), and separated busway…”

Speed Bumps with gaps for emergency vehicles to speed through? Cool!

Wonder how they propose to get regular vehicles to cross “over” the speed bump instead of just “speeding through the gaps” like the emergency vehicles would?

I guess we’ll just have to read The Manual to find out!

P.S. Next time you’re in New York City, don’t forget to wear your favorite walking shoes!