Alameda County Public Works Agency
399 Elmhurst Street, Hayward, California 94544 (510) 670-5480
Traffic Calming Measures
The following section traffic calming measures outline the different levels of traffic calming and the required approval process for each designated level. These traffic calming measures can be implemented individually or in combination. However, not all measures will be feasible or acceptable in all locations.
This section defines each level in the order of implementation of traffic calming measures. It also serves as a guide in the decision-making process for determining the best possible treatment for specific traffic issues within a community.
Level 1 Traffic Calming:
Requires no physical roadway modifications
Approval authority: Director of Public Works Agency with District supervisor
- Roadway Centerline
- Speed Enforcement
- Neighborhood Speed Watch Program
- Residential Neighborhood Gateway
- Street Trees
Level 2 Traffic Calming:
Requires minor physical roadway modifictions
(e.g., raised ceramic tiles, painted legends, striping)
Approval authority: Director of Public Works Agency with District supervisor
Level 3 Traffic Calming:
Requires major physical roadway modifications (e.g., extension of curb lane into roadway, uneven roadway surface)
Approval authority: Director of Public Works Agency with District supervisor
Level 4 Traffic Calming:
Measures physically prohibit vehicular travel to a certain degree (e.g., detours to parallel routes). These are not applicale on collector roadways.
Approval authority: Director of Public Works Agency with District supervisor
Level 1 Traffic Calming:
Roadway Centerline
Removing the roadway centerline striping "softens" the appearance of a roadway, altering motorist perception, and creating a more residential and local visual character for the roadway. With the elimination of centerline delineation, motorists tend to drive closer to the center of the roadway, sharing lanes with opposing traffic and creating roadside area for pedestrians and on-street parking.
Typically, centerline striping is installed on roadways with horizontal and vertical curves in order to separate motorists to improve traffic safety. Unfortunately, striping provides motorists with a sense of security of the travel lane, as well as, delineates major travel thoroughfares for those looking for "shortcuts."
By removing centerlines where not needed for safety, several neighborhood benefits may be achieved:
- Eliminates roadway visual identification as a bypass routes
- Creates the appearance of a minor residential roadway
- Allows motorists to drive towards the center of the roadway
- Reduces the potential for hit-parked-vehicle type collisions thereby encouraging residents to park on the roadway and not on the sidewalk area providing improved access and safety for pedestrians
- Typically reduces motorist speeds by eliminating clearly defined travel lanes, creating a shared roadway
Centerlines will remain where necessary to guide motorists around horizontal or vertical curves. While this traffic calming measure may lose its effectiveness to everyday users over time, its impact should be effective on occasional users.
IMPLEMENTATION GUIDELINES
The County is currently implementing this measure as a part of the on-going pavement maintenance program (slurry seal, chip seal, overlay, and reconstruction projects.) Rather than removing striping for specific roadways, it may be better to wait for a pavement rehab project or reschedule pavement rehab to include the subject roadway.
Level 1 Traffic Calming:
Speed Enforcement
Enforcement is tool that deters motorist from driving behavior that violates existing regulations for parking, driving maneuvers, and excessive speed. Enforcement of posted speed limits may be done by "selective enforcement" by the California Highway Patrol (CHP). Speed enforcement includes passive methods such as the use of a trailer that measures and displays the speed of motorists, but also includes the visual presence of CHP patrol and radar speed enforcement. Selective enforcement is most effective when done in conjunction with the neighborhood speed watch program.
Speed enforcement is effective in creating a heightened visual awareness of motorist speed in neighborhood areas. An additional impact of enforcement is the imposition of penalties upon driving behavior that may create unsafe roadway conditions. Radar enforcement requires compliance with the requirements of the California Vehicle Code and approval and support of the Board of Supervisors and the CHP.
IMPLEMENTATION GUIDELINES
Selective enforcement is implemented with the cooperation of the CHP as the enforcement agency: radar speed enforcement can only be implemented where concurrence and commitment from the CHP can be obtained.
Level 1 Traffic Calming:
Neighborhood Speed Watch Program
The speed watch is an educational program which requires the involvement and commitment from the neighborhood. Our experience indicates that the majority of motorists who drive above the posted speed limit live in the area. As part of the Speed watch program, neighborhood residents will receive a "Drive 25" flyer informing them about traffic issues in their community and the need for their participation to relieve the concerns. Thus, this approach targets the primary offenders.
Neighborhood participation includes the following:
- Identify motorists who drive at excessive speeds - vehicle type, color, license plate, time of day, etc. This information -will be forwarded to the CHP for follow-up which may include selective enforcement at the specified times or a visit to the residence of the owner of the identified vehicle.
- Observe Public Works staff collecting speed data using radar equipment. Radar equipment may be loaned to residents to assist in speeding motorist identification.
- Promotes neighborhood involvement to address traffic issues (excessive speed as well as other community concerns)
This program can be very effective and efficient since it heightens motorist awareness of driving behavior and its impact on the residents; it also provides the CHP with specific times for selective enforcement, and requires a joint effort from the community to regain control of its roadways.
IMPLEMENTATION
This is a mandatory level one measure for the Neighborhood Traffic Calming program. An example of the flyer is shown on the next page. Public Works will collect data, prepare the flyer, and send it out to the identified "neighborhood." This will be one opportunity to have the block captains or neighborhood leaders observe in the field data collection and the use of radar equipment.
Level 1 Traffic Calming:
Residential Neighborhood Gateway
Converting the entrance of a residential area into a neighborhood gateway. This can be done by means of an entry structure or signing in conjunction with other aesthetic features to emphasize the residential neighborhood. Gateways are typically constructed by newer large residential development projects to identify the development community.
Typically, motorists frustrated by congestion on major arterial and collector roadways will seek shortcuts or less congested routes. By providing high quality gateway features at the entrance to a residential neighborhood, some bypass traffic may be discouraged. In addition, gateways may improve the identity of the neighborhood generating more community involvement to preserve neighborhood character.
Some of the negative effects of this traffic calming measure may include the potential for vandalism and the cost to provide a high quality entry feature. Typically, entry structures would be installed on private property.
IMPLEMENTATION
Gateways would be installed at a natural entry to a residential neighborhood, especially where the neighborhood boundary changes in character (i.e. from a rural or commercial area to a residential area). The design of the gateway should be a high-quality design that reflects the character of the residential neighborhood.
Implementation will typically require the use of private property; the cooperation and concurrence of the property owner will be required and cannot be assured. Maintenance of the gateway would be the responsibility of the neighborhood.
Level 1 Traffic Calming:
Street Trees
Install street trees behind the sidewalk or pedestrian pathway along the length of the roadway. This traffic calming measure attempts to narrow the visual corridor of the roadway. Narrowing the visual corridor may influence motorists to drive more cautiously (hopefully slower) because of the apparent reduction of the "shy" distance along the roadway. Without street trees, the visual corridor may be defined in part by the front of houses. By adding street trees, the visual corridor becomes defined by the tree canopies which are closer to the roadway.
Street trees provide several community advantages as well as inconveniences:
- Narrows the visual corridor along the roadway influencing motorists to drive more cautiously.
- Improves the aesthetic character of the community.
- Provides a buffer between the roadway and residences.
- Trees may take time to mature in order to provide the desired effect.
- There is a maintenance responsibility for the tree assumed by the property owners.
- The potential for uplifting of the sidewalk is increased.
- There is a potential for an increase of safety and liability issues
IMPLEMENTATION
Implementation of this traffic calming measure requires the cooperation and support of the property owners along the roadway since street trees will be the responsibility of the property owner per the Alameda County Tree Ordinance. However, street trees will not be needed at every property to get the desired effect of narrowing the visual corridor - however, more street trees improve the residential character of the neighborhood.
The County occasionally receives grants for street trees. However, if trees are not available from the County, other sources of street trees will need to be identified.
Level 2 Traffic Calming:
Rumble Strips
Rumble strips consist of a pattern of raised ceramic pavement markers applied to the pavement to alert motorists of a change in roadway conditions ahead. They transmit vibration and sound to the motorists which refocuses attention back to the roadway.
There are two primary uses of rumble strips as a traffic calming measure:
- Rumble strips can provide advance warning of a change in neighborhood characteristics ahead. For instance, it can be used in conjunction with gateway treatments, centerline changes, street tree treatments, etc. to alert motorists that they are entering an area where they should drive with caution.
- Rumble strips can also create an area with an uncomfortable roadway surface which may influence motorists to drive slower.
Some of the issues regarding rumble strips include the following:
- The noise and vibration created by the rumble strips affects the adjacent residences.
- Bicyclists and motorcyclists may have experience difficulty riding over the ceramic markers.
- Motorists tend to swerve to avoid driving over the rumble strips.
- Influence on motorists speed may be minimal or site specific.
IMPLEMENTATION
Rumble strips can be installed to emphasize traffic calming measures or other unexpected roadway conditions. However, due to the noise and vibration created by rumble strips, written concurrence from the adjacent property owner will be required prior to installing rumble strips.
Level 2 Traffic Calming:
Highlighted Pedestrian Crossings
The primary function of pedestrian crosswalks is to concentrate pedestrians at a single crossing location, most desirably at intersections. Pedestrian crossings can be highlighted in order to accentuate the visibility of the crossing to motorists. Measures to incorporate this include using materials other than standard asphalt concrete (AC) such as textured concrete, raising the crossing above the roadway grade, or adding additional pavement markings (paint) within the existing crossing (additional pavement markings could be considered a Level 1 traffic calming measure.)
As a part of the annual pavement rehab program (slurry seal, chip seal, etc.) throughout the County, crosswalks that do not congregate pedestrians to a centralized crossing will be recommended for removal. Typically, pedestrians develop a false sense of security at crosswalks and tend to enter the roadway without looking for approaching vehicles. However, where crosswalks are appropriate, measures can be taken to emphasize the crossings.
A textured surface project would be a Level 2 traffic calming measure. The type of material selected would determine the effectiveness of this measure. Care must be taken to select a design that increases visibility and does not create tripping conditions such as cracks or raised asphalt "lips." Although the expected effect of highlighted crossings on motorist speed is minimal, it may increase motorists awareness of pedestrian activity in an area.
A raised crosswalk would be similar to a speed hump or other physical device and thus will be discussed with the Level 3 traffic calming measures.
IMPLEMENTATION
Prior to the highlighting of any crossing, the crossing must be determined to be necessary (i.e. on a safe-route-to-school, adjacent to major pedestrian generators such as commercial areas, or at locations with demonstrated conflicts between pedestrians and vehicles). Once this is determined, the type of crossing highlighting, if any, should be decided. There is a cost associated with the textured crossing along with potential noise; the additional markings may be more slippery when wet.
Highlighted crossings may also be used in conjunction with Level 3 traffic calming measures.
Level 3 Traffic Calming:
Bulb-outs
Bulb-outs narrow the roadway width at an intersection by modifying the curb return providing a physical constraint at an intersection which forces motorists to "slow down" in order to pass through the narrower roadway section. This measure is typically constructed at intersections, but mid-block locations may be considered.
This type of measure introduces two traffic calming concepts: physical constraints and visual traffic calming. Level 3 traffic calming involves physical constraints which produces a point speed reduction and pedestrian-friendly crossings. Point speed reductions may occur at bulb-outs, but motorist speed beyond the bulb-outs are typically either unaffected or higher than before installation. Visual traffic calming involves installing features which provide visual breaks along long sections of roadway to make the roadway appear either shorter or as a not a through route.
Bulb-outs offer several benefits to a neighborhood. These include the following:
- Visual traffic calming effect and possible point speed reduction
- Highlights intersections for motorists
- Reduces length of crossings for pedestrians
- Provides opportunities for landscaping
- No adverse effect on emergency vehicle access
There are some design obstacles and with bulb-outs. These include the following:
- Storm drain, street lighting, sewer, and other utilities may be affected and require relocation
- Reduces available on-street parking spaces
- Forces bicyclists into the travel lane with motorized vehicles
IMPLEMENTATION
Beneficial on long, straight, and flat roadway sections where visual traffic calming effects apply. Due to pedestrian benefits, consideration should be given to high pedestrian use intersections (adjacent to schools, commercial centers, etc.). Design considerations include accommodating large vehicles (fire trucks, garbage trucks, moving vans, etc.), street lighting, maintaining drainage system, allowing bicycle access, and landscaping and the associated maintenance and sight distance issue
Level 3 Traffic Calming:
Chicanes
A chicane (shi-kane) is a two or three section curb protuberance that forces motorists to maneuver through a narrow, single or two lane angled roadway section at a midblock location. Single lane chicanes restrict two-way traffic, requiring motorists to alternate traversing the narrow one lane roadway section. Two lane chicanes (also called "tadpoles") accommodate two directional flow simultaneously.
On single lane chicanes, if one does not encounter opposing traffic, the chicane forces one to drive slowly through the traffic calming device resulting in a point reduction in speed. Motorists encountering opposing traffic may have to yield for opposing vehicles to pass before proceeding. A "tadpole" chicane would function similarly to a mid-block traffic circle.
Chicanes introduce two traffic calming concepts: physical constraints and visual traffic calming. Level 3 traffic calming involves physical constraints which produces a point speed reduction. Point speed reductions may occur at a chicane, but motorist speed beyond the chicane are typically either unaffected or higher than before installation, unless used within a -system of traffic calming measures. Visual traffic calming involves installing features which provide visual breaks along long sections of roadway to make the roadway appear either shorter or as a not a through route.
Chicanes offer several benefits to the neighborhood. These include the following:
- Visual traffic calming effect and point speed reduction
- Opportunities for landscaping
- Minimal impact to emergency vehicle access.
Design considerations and negative impacts include the following:
- Possible increase in speeds beyond the chicane
- Increased noise at the chicane
- Removal of on-street parking
- May divert traffic to other adjacent roadways
- Increased potential for motorists hitting the curb
IMPLEMENTATION
Beneficial on long, straight, flat roadway sections where visual traffic calming effects apply. Design considerations should include street lighting, accommodating large vehicles (fire trucks, garbage trucks, moving vans, etc.), advance signing, maintaining adequate drainage, bicycle access, landscaping, and the associated maintenance and sight distance issues.
Level 3 Traffic Calming:
Single-lane Slow Points
A single-lane slow point is similar to a chicane except that there is no skew or angle in the roadway reduction. It provides a narrow roadway section along the roadway centerline which allows only one vehicle to pass at any time.
IMPLEMENTATION
Beneficial on long, straight, flat roadway sections where visual traffic calming effects apply. Design considerations should include street lighting, accommodating large vehicles (fire trucks, garbage trucks, moving vans, etc.), advance signing, maintaining adequate drainage, bicycle access, landscaping, and the associated maintenance and sight distance issues.
Level 3 Traffic Calming:
Road Humps
Road humps are a smaller version [50 mm (2 inches) high as opposed to 75 mm (3 inches)] of speed humps. The purpose of road humps is to alert motorists to the residential area and their driving characteristics rather than as a speed attenuator or bypass traffic deterrent.
A road hump does not provide a significant jarring sensation to a motorist. Rather, it provides a subtle disruption which may make motorists more aware of their surroundings - similar to rumble strips.
The application of road humps is similar but less restrictive than the speed hump. The applicable grades are up to eight percent (8%) and the warrant criteria requirements are not as restrictive.
IMPLEMENTATION
May be applicable on roadways up to eight percent (8%) grade with less restrictive application of warrant criteria. Impact to speeds and as a bypass deterrent is minimal. However, impacts to motorist awareness may be increased
Use the following guidelines for installation of speed humps vs. road humps
- Residential roadways with feasible alternative routes and grades less than or equal to five percent (5%)
- Install Road Humps
- Residential roadways with no feasible alternative routes and grades less than or equal to eight percent (8%)
- Install Road Humps
- Minor collector roadways with feasible alternative routes and grades less than or equal to five percent (5%)
- Install Road Humps
- Minor collector roadways with no feasible alternative routes and grades less than or equal to eight percent (8%)
- Install Road Humps
Level 3 Traffic Calming:
Speed Humps
A speed hump is a raised pavement section which requires motorists to drive at a reduced speed over an undulation. Speed humps differ from speed bumps (typically used in parking lots) in that humps are typically 3.7 m (12 feet) long as opposed to 0.6 m (2 feet) for speed bumps. The longer length of the speed hump increases the impact to vehicles at higher speeds and is more comfortable at lower speeds. The typical height of speed humps is 75 mm (approximately 3 inches.)
Speed humps, unlike the other level 3 traffic calming measures, provide only a physical constraint to produce a point speed reduction. While speeds will be reduced at the speed hump, motorists speed beyond the speed hump will are typically found to be unaffected or higher than before. No visual traffic calming benefits are achieved with speed humps.
Due to the jolt created by driving over the speed hump, traffic will be diverted to other adjacent roadways. While this diversion may benefit the roadway with the speed hump, the impact of the diversion to the entire identified neighborhood must be considered. Speed humps installed in areas without curb and gutter improvements may result in motorists driving on private property to avoid the speed hump. Fire trucks and other heavy vehicles are also affected due to the weight of the trucks. In addition, long term, everyday use of the speed hump can cause motorist frustration.
If applied correctly, speed humps can benefit a roadway:
- Reduces motorist speeds at and between speed humps if properly spaced
- Discourages bypass traffic
- Least expensive Level 3 traffic calming measure
Speed humps have several negative impacts. These include the following:
- Unfamiliar or inattentive motorists may lose control of their vehicles
- Increases emergency response times and impacts emergency vehicle equipment
- Undesired diversion of traffic to adjacent residential roadways
- No visual traffic calming effects
- Point speed reduction may have minimal impact beyond the speed hump
- Increased vehicle noise at the speed hump due to braking and acceleration
- Neighborhood aesthetics are affected by speed humps and the associated signing and pavement markings
IMPLEMENTATION
- Impacts motorcyclists and bicyclists
- Define the "neighborhood" to identify potential affected residential roadways. If other roadways will be impacted, concurrence for the installation of the speed hump on the study roadway must be received from two-thirds of the property owners on those impacted roadways.
- Identify primary emergency response routes
- Identify AC Transit service routes
- Roadway section must be straight and flat. In flat areas with adjacent hills, primary consideration must be given to maintaining traffic safety
- Meet warrants for speed hump installation
- Provide street light at each speed hump
Use the following guidelines for installation of speed humps vs. road humps
- Residential roadways with feasible alternative routes and grades less than or equal to five percent (5%)
- Install Speed Humps
- Residential roadways with no feasible alternative routes and grades less than or equal to eight percent (8%)
- Install Speed Humps
- Minor collector roadways with feasible alternative routes and grades less than or equal to five percent (5%)
- Install Speed Humps
- Minor collector roadways with no feasible alternative routes and grades less than or equal to eight percent (8%)
- Install Speed Humps
Level 3 Traffic Calming:
Raised Crosswalks
Raised crosswalks are similar to speed humps except that these are installed at intersections to elevate crosswalks. This type of traffic calming measure can be expanded to include the entire intersection (raised intersection).
Raised Crosswalks and Intersections, due to similar vehicle and neighborhood impacts, must meet the same criteria as Speed Humps as well as Highlighted Crossings. Raised crosswalks do provide benefits to pedestrians which are not provided by the speed hump.
Raised crosswalks and intersections may be difficult and expensive to install due to drainage requirements. In addition, raised crosswalks and intersections create turning maneuver problems at intersections.
IMPLEMENTATION
Must satisfy the criteria of both Highlighted Crossings and Speed Humps.
Level 3 Traffic Calming:
Roundabouts
A roundabout is a landscaped circular island located in the center of a residential intersection. Traffic drives to the right of the roundabout in a counterclockwise direction for all movements (left-turn, straight, and right-turn) Right-of-way assignment with a roundabout is given to those within the circle whereas those entering the roundabout must yield.
This type of measure introduces two traffic calming concepts: physical constraints and visual traffic calming. Level 3 traffic calming involves physical constraints which produces a point vehicle speed reduction. Point speed reductions may occur at the roundabout. But motorists speed beyond the roundabout are typically either unaffected or higher than before unless applied as a system of devices. Visual traffic calming involves installing features which provide visual breaks along long sections of roadway to make the roadway appear either shorter or as a not a through route. Roundabouts may also serve as gateways (see Level 1) to a community or to a system of traffic calming measures.
Roundabouts function somewhat similarly to bulb-outs except that vehicles must deviate from their path to drive past this traffic calming measure, thus impacting motorists speed more than bulb-outs. Visual traffic calming effects are greater with roundabouts than with bulb-outs. However, pedestrian accessibility with roundabouts is much more difficult and addressing vehicle access (turning radii) becomes more of an issue. Advance signing and pavement markings are usually installed for roundabouts to minimize collision potential.
IMPLEMENTATION
Roundabouts are beneficial on long, straight, and flat roadway sections where visual traffic calming effects or gateway features may apply. This traffic calming measure is not recommended along major collector roadways, at intersections with significant pedestrian activity, nor at intersections with levels-of-service C or worse due to the potential for motorists confusion. (level of service (LOS) is a measure of efficiency from a user perspective (LOS A being very efficient through LOS F, which is gridlock)). Design considerations include accommodating larger vehicles (particularly fire trucks), street lighting, landscaping, and the associated maintenance and sight distance issues.
Level 4 Traffic Calming:
Diverters/Forced Turn Channelization
A diverter is a physical measure constructed diagonally across an intersection which forces traffic to turn right or left. Diverters eliminate through traffic and forces traffic onto sidestreets.
Diverters effectively reduce bypass traffic, however their effect on motorist speed depends on the length of the block. Other benefits are the improved pedestrian and motorist safety at the intersection by eliminating conflicts, areas provided for landscaping, and the maintained through access for bicycles.
The negative aspects .of diverters are that traffic is diverted to other roadways and thus, creates traffic issues on other roadways. Emergency vehicle access may also be diverted, increasing emergency response. The diversion may also prove to be a great inconvenience to some residents gaining access to their property. Additionally, the installation of diverters may require the reconstruction of the entire intersection and the acquisition of right-of-way from adjacent property owners.
While diverters offer tremendous traffic calming and aesthetic benefits to a roadway, the entire neighborhood is affected by this type of traffic calming measure.
IMPLEMENTATION
- Define the "neighborhood" to identify potential affected residential roadways. If other roadways will be severely impacted, 90% concurrence from property owners on those impacted roadways must be received for the installation of the diverter at the study intersection.
- Identify primary emergency response routes
- Identify AC Transit service routes
- Design must accommodate turning of large vehicles
- Landscaping should consider maintenance and sight distance issues
- Requires Board of Supervisors Resolution
Level 4 Traffic Calming:
Half (one-way) Roadway Closure
A half (one-way) roadway closure is a physical measure constructed to allow one-way traffic only at an intersection. This is similar to the chicane described in the level 3 traffic calming measures except that this device allows only one way traffic.
Half closures (which may also provide potential areas for landscaping) effectively reduce bypass traffic in one direction. Motorist speeds in the direction of unrestricted traffic may be unaffected. However, since this is used at an intersection, STOP controls may apply.
Disadvantages to half closures include the diversion of traffic to other roadways, partial emergency vehicle impediment, and the inconvenience to residents.
IMPLEMENTATION
- Define the "neighborhood", to identify potential affected residential roadways. If other roadways will be severely impacted, 90% concurrence from property owners on those impacted roadways must be received for the installation of the half (one-way) roadway closure at the study intersection.
- Identify primary emergency response routes
- Identify AC Transit service routes
- Design must accommodate turning of large vehicles
- Landscaping should consider maintenance and sight distance issues
- Requires Board of Supervisors Resolution
Level 4 Traffic Calming:
Full Roadway Closure
A full roadway closure is a physical measure constructed to essentially cul-de-sac a roadway at an intersection.
Full closures (which may also provide potential areas for landscaping) effectively reduce bypass traffic. Motorist speeds would be similar to cul-de-sac roadways with the same roadway geometry.
Disadvantages to full closures include the diversion of traffic to other roadways, increase of emergency response times, and the inconvenience to residents.
IMPLEMENTATION
- Define the "neighborhood" to identify potential affected residential roadways. If other roadways will be severely impacted, 90% concurrence from property owners on those impacted roadways must be received for the installation of the full roadway closure at the study intersection.
- Identify primary emergency response routes
- Identify AC Transit service routes
- Design must accommodate turning of large vehicles
- Landscaping should consider maintenance and sight distance issues
- Requires Board of Supervisors Resolution
