Speed Bumps And Speed Humps

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.

When any new traffic management approach is introduced, issues, concerns, and questions are bound
to arise. Design decisions related to traffic can have far-reaching consequences. Lives, economic well-being, and urban livability are directly affected.

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.

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.