Slow Point Examples: Medians

Medians

Medians are islands located along the roadway centerline, separating opposing directions of traffic
movement. They can be either raised or flush with the level of the roadway surface. They can be expressed as painted pavement markings, raised concrete platforms, landscaped areas, or any of a variety of other design forms. Medians can provide special facilities to accommodate pedestrians and
bicyclists, especially at crossings of major roadways.

Design Considerations:
• Medians are most valuable on major, multi-lane roads that present safety problems for bicyclists
and pedestrians wishing to cross. The minimum central refuge width for safe use by those with
wheelchairs, bicycles, baby buggies, etc. is 1.6 meters (2 meters is desirable).
• Where medians are used as pedestrian and bicyclist refuges, internally illuminated bollards are suggested on the medians to facilitate quick and easy identification.
• Used in isolation, roadway medians do not have a significant impact in reducing vehicle speeds. For the purpose of slowing traffic, medians are generally used in conjunction with other devices, such as curb extensions or roadway lane narrowing.

Several caveats apply:
• To achieve meaningful speed reductions, the travel lane width reduction must be substantial and visually obvious. The slowing, however, is temporary; as soon as the roadway widens again, traffic resumes its normal speed.
• Bicyclists have been put at risk of being squeezed where insufficient room has been left between a central median and the adjacent curb. Experience shows that most drivers are unlikely to hold back in such instances to let bicyclists go through first. This threat is particularly serious on roads with high proportions of heavy vehicles.
• The contradiction between the need to reduce the roadway width sufficiently to lower motorist speeds, while at the same time leaving  enough room for bicyclists to ride safely, must be addressed. This may be achieved by reducing the roadway width to the minimum necessary for a bicyclist and a motorist to pass safely (i.e., 3.5 meters).

There are three suggestions:
• Introducing color or texture changes to the road surface material around the refuge area reminds motorist that a speed reduction is intended.
• White striping gives a visual impression that vehicles are confined to a narrower roadway than that created by the physical obstruction — adjacent areas exist that vehicles can run over, but these are not generally apparent to approaching drivers.
• In some cases, provide an alternate, cut-through route for the bicyclists.

Next… Slow Point Examples:Curb Extensions

2. Reducing street areas where motor traffic is given priority. This category of traffic-calming includes all those that reduce the area of the street designated exclusively for motor vehicle travel. “Reclaimed” space is typically used for landscaping, pedestrian amenities, and parking.

Discussed here are:
• Slow points.
• Medians.
• Curb extensions.
• Corner radius treatment.
• Narrow traffic lanes.

Slow Points (neck-downs, traffic throttles, pinch points) - Slow points narrow a two-way road over a short
distance, forcing motorists to slow and, in some cases, to merge into a single lane. Sometimes these are used in conjunction with a speed table and  coincident with a pedestrian crossing. The following are advantages and disadvantages of both one-lane and two-lane slow points:

(1) One-lane slow point.
One-lane slow points restrict traffic flow to one lane. This lane must accommodate motor traffic in both travel directions. Passage through the slow point can be either straight through or angled.
Advantages:
• Vehicle speed reduced.
• Most effective when used in a series.
• Imposes minimal inconvenience to local traffic.
• Pedestrians have a reduced crossing distance, greater safety.
Disadvantages:
• Reduced sight distances if landscaping is not low and trimmed.
• Contrary to driver expectations of unobstructed flow.
• Can be hazardous for drivers and bicyclists if not designed and maintained properly.
• Opposing drivers arriving simultaneously can create confrontation.

(2) Two-lane slow point.
Two-lane slow points narrow the roadway while providing one travel lane in each direction.
Advantages:
• Only a minor inconvenience to drivers.
• Regulates parking and protects parked vehicles as the narrowing can help stop illegal parking.
• Pedestrian crossing distances reduced.
• Space for landscaping provided.
Disadvantages:
• Not very effective in slowing vehicles or diverting through traffic.
• Only partially effective as a visual obstruction.

Design Considerations:
• Where slow points have been used in isolation as speed control measures, bicyclists have felt squeezed as motorists attempt to overtake them at the narrowing. Not all bicyclists have the confidence to position themselves in the middle of the road to prevent overtaking on the approach to and passage through the narrow area.
• To reduce the risk of bicyclists’ being squeezed, slow points should generally be used in conjunction
with other speed control devices such as speed tables at the narrowing. Slower moving drivers will be more inclined to allow bicyclists through before trying to pass. Where bicycle flows are high, consideration should be given to  a separate right-of-way for bicyclists past the narrow area.
• A textured surface such as brick or pavers may be used to emphasize pedestrian crossing movement. Substituting this for the normal roadway surface material may also help to impress upon motorists that lower speeds are intended.
• Such measures should not confuse pedestrians with respect to the boundary of the roadway area over which due care should still be taken. In particular, where a road is raised to the level of the adjacent sidewalk, this can cause problems for those with poor sight. However, a tactile strip may help blind people in distinguishing between the roadway and the sidewalk; similarly, a color variation will aid those who are partially sighted.
• Slow points can be used to discourage use of the street by large vehicles. They can, however, be barriers to fire trucks and other emergency vehicles. Some designs permit access by emergency vehicles by means of lockable posts or ramped islands.
• Slow points can enhance the appearance of the street. For example, landscaped islands can be installed, intruding into the roadway to form a narrow “gate” through which drivers must pass. Landscaping enhances the neighborhood’s sense of nature and provides a visual break in views along the street.
• Slow points are generally only sanctioned where traffic flows are less then 4,000 to 5,000 vehicles per day. Above this level, considerable delays will occur during peak periods.
• Clear signing should indicate traffic flow priorities.

Next… Slow Point Examples

Intersection humps raise the roadway at the intersection, forming a type of “plateau” across the intersection, with a ramp on each approach.  The plateau is at curb level and can be enhanced through the use of distinctive surfacing such as pavement coloring, brickwork, or other pavements. In some cases, the distinction between roadway and sidewalk surfaces is blurred. If this is done, physical obstructions such as bollards or planters should be considered, restricting the area to which motor vehicles have access.

Design Considerations:
• Ramps should not exceed a maximum gradient of 16 percent.
• Raised and/or textured surfaces can be used to alert drivers to the need for particular care.
• Distinctive surfacing helps reinforce the concept of a “calmed” area and thus plays a part in reducing vehicle speeds.
• Distinctive surfacing materials should be skid-resistant, particularly on inclines.
• Ramps should be clearly marked to enable bicyclists to identify and anticipate them, particularly under conditions of poor visibility.
• Care must be taken so the visually impaired have adequate cues to identify the roadway’s location (e.g., tactile strips). Color contrasts will aid those who are partially sighted.

Next… Traffic Calming - Reducing Street Area Where Motor Vehicle Traffic is a Priority.

(Continued from Bumps, Humps, & Other Raised Pavement Areas)

Raised crosswalks are essentially broad, flat-topped speed humps that coincide with pedestrian crosswalks at street intersections. The crosswalks are raised above the level of the roadway to slow traffic, enhance crosswalk visibility, and make the crossing easier for pedestrians who may have difficulty stepping up and down curbs.

Raised Crosswalks Design Considerations:
• Can be constructed of brick, concrete block, colored asphalt or cement, with ramps striped for
better visibility.
• Raised crosswalks are applicable:
(1) On roadways with vehicular speeds perceived as being incompatible with the adjacent residential                       land uses.
(2) Where there is a significant number of pedestrian crossings.
(3) In conjunction with other traffic-calming devices, particularly entry treatments.
(4) On two-lane or fewer residential streets classified as either “local streets” or neighborhood
collector streets.”
(5) On roadways with 85th percentile speeds less than 45 mph.

Next… Intersection Humps/Raised Intersections

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

Professional engineers, planners, government, and the public all are aware of and sensitive to proposals
for changes in the traffic environment. Roadway congestion, air quality, traffic safety, street crimes,
and the high cost of new improvements are among the most-widely debated issues in America today. New design ideas are, and should be, subjected to rigorous testing and evaluation before being accepted as
part of the standard engineering and transportation planning tool kit. Traffic calming is not a panacea for
urban transportation woes, but it can have significant benefits in many situations.

In considering the application of traffic-calming techniques, what specific issues are likely to arise? The discussion on the following pages focuses on traffic-calming issues.

1. Traffic safety.

The Issue: Encouraging people to walk, play, and bicycle in and next to the streets is just asking for trouble. They will have a false sense of security and accidents will increase. They will develop bad habits that may increase their when they leave the neighborhood.

Comment: Traffic-calming measures have been implemented in many European cities. In the Netherlands and Germany, extensive research has been conducted to evaluate the safety and impact of traffic-calming techniques and devices.
2. Impact on traffic volumes, distribution, and operations.

The Issue: Traffic calming will never work on anything except very low-volume residential streets. It will substantially reduce the amount of traffic that a street can handle efficiently and this is counterproductive.
We need to move vehicles, not restrict them.  Furthermore, if we slow traffic on one streets, the traffic will simply be diverted to another street. The net result will be increased congestion and more problems overall.

Comment: A 5-year German Federal Government evaluation of traffic calming and follow-up research
found:
• Little change in overall traffic volumes.
• Reduction in average vehicle speeds by almost 50 percent.
• Average increase in motorist trip time of only 33 seconds.

3. Lack of proven design standards.

The Issue: There are no uniform, accepted, and legally defensible standards to follow. If we want to try traffic calming, where can we get specific information about design?
Comment: Many U.S. cities are now developing and testing design guidelines for traffic-calming improvements. Although uniform, national standards have yet to evolve, valuable experience is being gained. The list of references in this blog provides a starting point for further exploration of
specific design approaches.
4. Liability.
The Issue: These traffic-calming ideas may be accepted in Europe, but they haven’t really been tried here. Are we opening the door to all kinds of legal problems if somebody crashes on a traffic circle or a speed table and sues us?

Comment: When considering the use of any new design approach, concerns about liability can be addressed somewhat through performance of “due diligence” on the part of the engineer, planner, or other professionals involved in the design. Research into the experiences of other U.S. cities, European standards, and evaluation studies should be thorough and followed up with a first-hand look if possible. Construction of a pilot project or other testing of proposed designs can benefit, as can ongoing and systematic valuation of the improvements once installed.

5. Emergency and service vehicle access.

The Issue: Construction of speed bumps, neckdowns, medians, and traffic circles will increase response times for emergency vehicles and may restrict access for garbage trucks, delivery vans, and other large vehicles.

Comment: Studies in Berkley and Palo Alto, CA, show that traffic management measures (e.g., traffic diverters, bicycle boulevards) have not impaired police or fire emergency response times. • The Seattle Engineering Department works closely with its Fire Department to design and field-test traffic circles on a site-specific basis to ensure good emergency access.
6. Impacts on bicycling.

The Issue: Pavement texturing, speed tables, wider sidewalks, “bulb-outs” at corners and similar
improvements may make things better for pedestrians, but may have a negative impact on bicycling.
Emergency vehicle access should always be considered when incorporating traffic-calming
measures.

Comment: A 5-year German Federal Government evaluation of traffic calming and follow-up research found doubling of bicycle use over a 4-year period.

• Implementation of traffic management strategies in the downtownarea of the Dutch City of Groningen contributed to a substantial increase in bicycling and walking. Bicycle use is now well over 50 percent of all trips.
• Studies of traffic-calming areas in Japan show increases in both bicycle and pedestrian traffic volumes along most routes.

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.

Six Main Objectives of Traffic Calming

1. To encourage public involvement in the traffic calming process by incorporating the preferences & requirements of the citizens,
2. To reduce vehicular speeds,
3. To promote safe & pleasant conditions for motorists, bicyclists, pedestrians, & residents,
4. To improve the environment & livability of neighborhood streets
5. To improve real & perceived safety for non-motorized users of the streets,
6. To discourage use of residential streets by non-citizens cut through vehicular traffic.

Sounds good in theory but how does all this work practically.  Please provide your comments and experiences.

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.

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!