Speed Bumps And Speed Humps

Continued from…Reducing street area where motor traffic is given priority.

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

Continued from…Intersection Humps/Raised Intersections:

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/Raised Intersections
continued from Raised Crosswalks

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.

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.