Continued from Slow Point Examples:Corner Radius Treatment
Slow Point Examples: Narrow Traffic Lanes
Narrow Traffic Lanes
Especially in residential areas, wide streets may not be necessary or desirable. Wide traffic lanes
encourage faster motor vehicle speeds. Consideration should be given to the review of cross-sections
for all street classifications to determine whether roadway lane widths can be reduced (within
AASHTO guidelines) so more area can be dedicated to bicycle and pedestrian use and associated trafficcalming facilities.
• Additional area for landscaping, and pedestrian
• Reduced vehicle speeds and increased safety.
• On-street parking may be restricted.
• Cross-section approaching the reducedwidth street should also be slowed.
Example: City of Portland, Skinny Street Program The City of Portland requires most newly constructed
residential streets to be 20 or 26 feet wide, depending on neighborhood on-street parking needs. In the past, residential streets were required to be as wide as 32 feet. To achieve a variety of benefits, the City reduced residential street widths. The City’s Fire Bureau participated in the development of this standard to ensure access for emergency vehicles.
Next up… Street Closures
Continued from… Slow Point Examples: Medians
Another Slow Point Example are Curb Extensions
The sidewalk and/or landscaped area on one or both sides of the road is extended to reduce the roadway to a single lane or minimum-width double lane. By reducing crossing distances, sidewalk widening is used to facilitate easier and safer pedestrian movement. Reducing roadway width results in vehicle speed reductions. When curb extensions are used at intersections, the resultant tightened radii ensure that vehicles negotiating the intersection do so at slow speeds.
• Can be installed either at intersections or midblock.
• May be used in conjunction with other trafficcalming devices.
• Curb extensions are limited only to the degree that they extend into the travelway. Curb extensions cannot impede or restrict the operation of the roadway.
• Successful bicycle facilities need a clear separation from sidewalk and street pavement, with adequate distances from parked cars to avoid opening doors. Cross-traffic should be slowed to allow bicyclists better continuity and safety.
• Narrowing certain streets can, at the same time, create safer bicycle facilities, but care should be
taken that bicyclists are not squeezed by overtaking vehicles where the road narrows. Encouraging motorists to let the bicyclists through first by using complementary trafficcalming techniques such as speed tables and cautionary signing or leaving sufficient room for both to pass safely at the narrowing would be appropriate measures.
• If it is expected that a motorist should be able to pass a bicyclist, the minimum desirable width is
• Curb extensions can be employed to facilitate bicycle movement where a segregated multi-use trail crosses a busy street.
Next…Slow Point Examples:Corner Radius Treatment
Continued from…Reducing street area where motor traffic is given priority.
Slow Point Examples: 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.
• 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.
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.
• 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.
• Vehicle speed reduced.
• Most effective when used in a series.
• Imposes minimal inconvenience to local traffic.
• Pedestrians have a reduced crossing distance, greater safety.
• 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.
• 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.
• Not very effective in slowing vehicles or diverting through traffic.
• Only partially effective as a visual obstruction.
• 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.
• 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.