Design Guidelines for Traffic Calming Measures
Table of Contents
Raised Crosswalk and Raised Intersection……………………5
Sidewalk Extension……………………………………….. …9
Center Island Narrowing……………………………...19
Curb Radius Reduction……………………………………….19
Raised Median Island………………………………………...24
Median through an Intersection……………………………...39
Right In/Right Out Island…………………………………....41
Traffic Calming Signs……………………………………………...43
Speed Hump sign………………………………………….....43
Traffic Calmed-Neighbourhood sign………………………...44
Design Guidelines for Traffic Calming Measures
The purpose of this guide is to standardize the design procedures of traffic calming measures wherever possible in order to ease the implementation of effective traffic calming strategies in communities throughout North America. The information contained in this guide is not a strict set of standards because of certain instances where specifications may not be able to be met. The specifications presented are optimal, based on various research projects throughout North America, and should be used wherever it is possible and feasible to do so.
There are many general considerations that need to be addressed when designing any traffic calming measure.
• Grades: Maximum and minimum grades are put into place in order to minimize vehicle damage, loss of vehicle control, and reduce potential road or property maintenance due to problems such as poor drainage that could arise from traffic calming measures. An example of a minimum grade is raised crosswalks or raised intersections having at least a 1% cross slope for drainage purposes. Maximum grade must be considered when looking at implementing a vertical deflection on a sloped road. For example, the maximum grade for implementing a speed hump is 8%; anything more than this is thought to be potentially hazardous to a driver because of the high transition slope between the speed hump and the road.
• Long wheelbase and Emergency Vehicles: Knowledge of emergency vehicle routes and primary street usage must be acquired before implementing certain traffic calming measures because of the large turning radii of these vehicles. Many horizontal street calming measures such as traffic circles, chicanes, lateral shifts, and directional closures can be impassable for certain large vehicles, and therefore should be limited to residential use. Another option to accommodate large vehicles is using a mountable rolled curb around the perimeter of the horizontal measure.
• Ease of Passage for Other Street Users: Any traffic calming measure which sacrifices the safety and general use of the street to cyclists or pedestrians should not be implemented. Compatibility of street calming measures to other street users can often be accomplished fairly easy. For example, when implementing a speed hump, passage for bicycles can be obtained by leaving sufficiently wide gaps in the speed hump near the side of the street. Similarly, any street closure should include a walkway or path so it is still possible for pedestrians to access the neighbouring street.
• Surface Drainage: Surface Drainage is an important design consideration on both roadways and sidewalks because of the potential problems it can create for both the road and sidewalk condition, and also the safety of their users. All traffic calming fixtures should have a minimum cross-slope grade in order to promote drainage and reduce ponding or ice patches. On roadways with traffic calming measures that do not have drainage gaps, catch basins must be located at a higher elevation than the traffic calming measure if there is any grade to the roadway.
• Access to Underground Utilities: Whenever implementing a street calming measure, the accessibility of underground utilities must be ensured (Skene, Pg. 4-1 – 4-2).
• Desired Vehicle Speed: The desired vehicle speed through a traffic calmed area must be determined before the exact design dimensions of the traffic calming device can be specified. For horizontal traffic calming measures, the smaller the turning radius is, the slower the traffic will pass through the area. A formula from mechanics is used to relate the turning radius to the velocity of the vehicle.
|R |Maximum horizontal radius of the curve (ft) |
|V |Velocity of the vehicle around the curve (mph) |
|e |Superelevation rate |
|f |Side friction factor |
R = V 2
15 (e + f)
The superelevation rate is negligible in almost all urban areas. The side-friction factor is based on safety against skidding and level of discomfort, and can be determined from graphs and tables in the American Association of State Highway and Transportation Officials (AASHTO) “A Policy on Geometric Design of Highways and Streets”. The calculations of the curve radius apply only to single curves. They can only be used as general approximations for horizontal traffic calming measures involving more than one turn such as chicanes and traffic circles.
For vertical traffic calming measures such as speed humps, another mechanics formula can be used to calculate the centrifugal acceleration over a circular hump of a given radius.
|A |Acceleration (ft/sec2) |
|V |Velocity of vehicle over hump (mph) |
|R |Radius of hump (ft) |
|Constant |Conversion Factor |
A = 2.15 V 2
International traffic calming standards suggest that a vertical acceleration of up to 1 g (9.81 m/sec2) can be tolerable for short periods, however this is fairly high so personal discretion may be used to determine an appropriate sized speed hump (Ewing, pg. 67 – 69).
• Maintenance: Increased or more difficult street maintenance may occur as a result of traffic calming. Certain measures should be considered to minimize this negative effect. Snow plowing over vertical traffic calming elements may cause damage either to the snow plow or the street. Other traffic calming options or careful snow plow operating will be necessary to prevent damage on frequently plowed streets. Accumulation of snow or leaves may also occur as a result of some traffic calming measures so frequent removal may be required at certain times of the year.
• Materials: Materials for all traffic calming measures that will be used in sub-zero temperatures should be able to withstand repeated freeze-thaw action and heavy loads at least as well as the surrounding roadway material. Care should be taken to avoid any materials or paints that may be excessively slippery when wet.
• Signage: Though signs are usually required to inform road traffic of the traffic calming measure approaching, additional warning signs should be minimized for aesthetic reasons. It is unnecessary to erect any additional signs; if the traffic calming measures are navigated at the posted speed there is no risk of vehicle damage or loss of control (Skene, Pg. 4-2)
• Temporary Installations: Temporary traffic calming installations are often beneficial to determine an optimal location or specific design of a traffic calming measure before investing in a permanent fixture. Another advantage of a temporary installation is to judge community response to the device. Disadvantages of temporary traffic calming measures are primarily based on poor aesthetics, creating a public disapproval even for a similar permanent fixture that may be more pleasing. If a temporary traffic calming measure is aesthetically pleasing, it may be able to become a permanent fixture (Ewing, pg.82).
• Streetscaping/Landscaping: Adding streetscaping or landscaping to a traffic calming measure may considerably increase the cost and maintenance but can improve the measure both aesthetically and functionally. Effective landscaping on street calming measures can improve community acceptance by softening the appearance and giving a higher perceived functionality. Streetscaping and landscaping can also make a road seem narrower therefore reducing speeds. Specific streetscaping elements can include ornamental items such as lighting, benches, and planters as well as vegetation. When incorporating streetscaping or landscaping elements, it is important to maintain good visibility and not sacrifice street user safety (Skene, 4-2)
To maintain the highest level of safety and appearance, it is essential to adequately maintain all landscaping measures. There are a few different options when it comes to maintaining streetscaping and landscaping elements. The city of Seattle is a good example because of its extensive use of street calming measures. Seattle initially did all of the landscaping and maintenance for their traffic circles. As more and more circles were constructed the cost of maintenance became unaffordable for the city, so a community involvement program was put into place. The city does the initial landscaping of the measure and the neighbourhood residents are then responsible for any maintenance or replacement that may be necessary. This method generally worked well for Seattle, but there were some problems with neighbourhood negligence resulting in a wide range of landscaping quality on the traffic circles. Other cities such as Portland take full responsibility for construction and maintenance of their streetscaping and landscaping measures for liability and quality purposes (Ewing pg.82).
Vertical deflections include raised crosswalks, raised intersections, sidewalk extensions, speed humps and tables, and textured crosswalks. Vertical deflections are most effective in reducing traffic speeds rather than traffic volumes.
Raised Crosswalks and Raised Intersections - raised junctions, intersection humps, plateaus
Raised Crosswalk serving a dual purpose as a speed hump (Delaware Register of Regulations, Pg. 542).
A raised crosswalk can be implemented either mid-street or at an intersection as long as the boulevard is wide enough to accommodate the required elevation change at the maximum grade. The height of the raised crosswalk depends largely on desired vehicle speed (see Design Considerations), but should generally be high enough to discourage speeding but not produce a risk of vehicle damage or loss of control when navigated at the intended speed. Speed tables can also serve a dual purpose as raised crosswalks.
Raised Intersections are flat raised areas covering an entire intersection with ramps up on all sides (Ewing, pg.34). The flat top is often finished in brick or other suitable textured material for increased effectiveness and increased aesthetics. Like raised crosswalks, the height of the intersection depends on desired traffic speed, but should generally be suitable to reduce speeding while eliminating risk to drivers and their vehicles. Emergency and transit vehicle volume in the area should also be considered due to the decreased ease of use of large quickly moving vehicles on raised intersections, especially when turning.
The height of raised intersections and raised crosswalks should correspond throughout the community’s street network in order for citizens to get a better grasp of the design speeds and operations of the measure. A typical height for an intersection or crosswalk with a standard 2m ramp would be 80mm and could change according to the length of the ramp. The location of a raised crosswalk or intersection in relation to sidewalks and curbs should be identical to regular crosswalks or intersections. A minimum 15mm lip should be maintained at all sidewalk-crosswalk transitions to aid the visually impaired in acknowledging the presence of the intersection or crossing. The transition area between the sidewalks and the raised intersection should be lowered to a 15mm curb face height with a transition slope of no greater than 6%. This transition area should also have a textured finished such as stamped concrete to provide a physical indication of the presence of the crossing. Recommendations for these textured surfaces can be found in the “Geometric Design Guide for Canadian Roads” (GDGCR). The flat top of the raised intersection should have a minimum grade of 1% to promote drainage. The dimensions shown have proven to be the best compromise for emergency and transit vehicle passage, effective speed reduction, and drivability. Raised crosswalks and intersections should be keyed directly into the existing pavement to provide the most secure connection
A speed hump sign should be located directly beside a raised crosswalk facing traffic. If a raised crosswalk is located on a one way street, a speed hump sign should be placed on either side of the street facing traffic. The speed hump sign is necessary for a raised intersection in the same manner, unless the intersection is stop sign or stop light controlled in which case no sign is needed. Pedestrian crosswalk signs are necessary on either side of the raised crosswalk. Solid white reflective pavement markings such as arrows should also be included directly preceding raised crosswalks and intersections. No advance warning signs are recommended for either of these traffic calming measures in order to reduce redundancy and improve aesthetics.
(Skene, Pg. 4-4)
(Skene, Pg. 4-5)
Sidewalk Extension [pic]
Concrete sidewalk extension (Regina, SK).
There are two types of sidewalk extensions that can be used depending on whether the sidewalk and curb are aligned or if the sidewalk is separate from the curb with a boulevard in-between. In the first case, the sidewalk and curb are directly adjacent to the roadway so the extended sidewalk can continue across the intersection where a typical intersection crossing would occur. With a boulevard between the curb and the walk, the extended sidewalk is offset back from the typical intersection crossing. In both cases there must be adequate transition area from the regular sidewalk down to the extended sidewalk.
In the case where the sidewalk is joined to the curb, the transition area approaching the intersection crossing must not exceed a grade of 6% decreasing in elevation to a recommended height of 15mm across the intersection. For the separated curb and walk, the sidewalk is typically lowered in elevation to 40mm through the intersection with a 6% grade slope on either side for vehicle passage. Another option in this case is to construct a raised crosswalk instead of the extended sidewalk. The raised crosswalk can only be implemented if the distance between the sidewalk and the curb is at least 1.5m or preferably 2m to allow a proper transition slope.
Sidewalk extensions always occur at intersections; no additional signs or pavement markings are required.
(Skene, Pg. 4-7)
Textured crosswalks are put into place to further identify the location of a crosswalk to street users. Although textured crosswalks can be used alone, they are commonly used to enhance other traffic calming measures such as a raised crosswalk. The textured surface can be created by concrete stamping, exposed aggregate concrete, or by the use of a concrete paver. Since textured crosswalks rely on both physical and visual means to identify their location, added color can increase the effectiveness of the measure.
There are no specific design dimensions for textured crosswalks. The textured surface should be adequate to provide a visual and physical indication of the crosswalk, and should not be extreme enough to alter vehicle behaviour over the textured section.
No additional signs are required for a textured crosswalk. If pavement markings are required for another purpose in the textured area, coloured materials may be necessary for the textured area instead of painting over the textured surface.
Speed Hump - road humps, undulations [pic]
Speed humps are the most commonly used traffic calming device in North America because of their low price, easy construction, and effective results. Typically, speed humps will reduce vehicle speeds by 8 to 16 kph if placed properly. The Watts profile hump, a 3.6 meter parabolic hump between 7.5 and 10 cm high, with a typical design speed 24 of to 32 kph, is the single most widely used speed control measure in the United States. Speed humps have four common profiles that have been tested extensively throughout North America: sinusoidal, circular, parabolic, and flat-topped. In some cases a speed hump can be coupled with a textured surface to increase the effectiveness of the measure. Any type of speed hump should have the required dimensions to produce enough driver discomfort to reduce speed to the desired level without sacrificing safety to street users. A speed hump should be large enough to cause a vertical deflection in the suspension and body of a vehicle passing over it. A problem with older speed bumps was the suspension of a vehicle would quickly compress and rebound before any vehicle body movement took place if taken at speed. Ease of passage for emergency and transit vehicles must also be considered (Ewing, Pg. 31). Certain measures must also be taken to allow proper drainage and possibly easier bicycle passage.
The type of street in which speed humps are to be placed must be considered for the proper design dimensions to be used. For residential streets, the most common design in Canada is a sinusoidal profile 4m long hump with a height of 80mm (Skene, Pg. 4-6, 4-9). The Watts profile hump has traditionally been the most widely used hump in the U.S, but this 10 cm high design is quickly losing acceptance because of its severe harshness. Popular new designs being used in the U.S. are a 4.2 m hump with the same profile and height as the Watts, and the 6.6 m speed table. Collector streets generally use speed tables rather than speed humps. Speed tables are similar to speed humps with an extended flat top (Ewing, Pg.71). The 80mm height is still used, but the length increases to 7m. According to the Canadian Guide, the speed table is preferred in this case because of the higher design speed allowing easier access for emergency and transit vehicles. On either type of hump, a small drainage culvert should be included close to the curb to promote drainage. This drainage route can be widened to allow a cyclist to pass through; however different jurisdictions have varying views on the necessity of this procedure (Skene, Pg. 3-12).
There have been extensive tests conducted throughout North America on different profiles and dimensions of speed humps, many leading to a shift from speed humps to speed tables, also referred to as trapezoidal humps or speed platforms. The city of Portland, Oregon found that the standard 3.6 m Watts hump was too abrupt. Instead, they implemented 4.2 m parabolic humps or 6.6 m speed tables. The 7m speed tables were found preferable in many cases especially where there is high traffic volume and a high concentration of emergency and transit vehicles. The standard speed table used in the U.S. is 7.5 to 10 cm high with a 3 m table-top and 6 ft long ramps on either side (Ewing, Pg.32). The Canadian version of this is 80mm in height with 2m long ramps and a 3m long table. Some tables are enhanced with brickwork or a textured table surface for increased aesthetics and effectiveness. Since the 6.6 m table is long enough for the entire wheelbase of a vehicle to be on the flat top at once when crossing it, there is a less abrupt transition and almost no risk of bottoming out. The table design results in a higher design speed of 40 to 48 kph 1) (Ewing, Pg. 72). Speed tables can also be effective in serving a dual purpose as a raised crosswalk when placed appropriately. Speed tables tend to have a significantly higher public approval rating because of their superior aesthetics and less harsh ride. Although speed tables are a very effective device in many situations, they have some major drawbacks. Speed tables are expensive compared to a standard speed hump especially when enhanced with brickwork or a textured surface. Speed humps are also less successful in certain cases in solving a speeding issue because of their relatively
1) 85th percentile speeds
mild vehicle deflection. The 6.6 m table is only one design however, and dimensions can
be varied in order to achieve the desired traffic speed if necessary. In Boulder, CO, for example, speed tables were designed with heights of up to 6 inches, ramps of 2.25 to 3 m, and tables ranging from 5.4m to 6.9 m (Ewing, Pg. 32 – 34).
Speed humps and tables should always be keyed directly into the existing pavement during construction to provide the most secure connection and minimize damage to and from snow plow equipment.
A speed hump sign should be placed directly beside a hump facing traffic, and if a speed hump is located on a one-way street, a speed hump sign should be placed on either side of the speed hump facing traffic. White reflective pavement markings are also recommended directly preceding the speed hump (Skene, Pg. 4-9).
Engineering principles state that the more acute the horizontal curvature of a traffic circle, chicane or curb extension, the greater number of motorists will reduce their speed. For example, a horizontal curve with a radius of 12.9 m will normally reduce the speed of a regular sized vehicle to approximately 24 kph (Ewing, Pg. 68).
Chicane - deviation, serpentines, reversing curves, or twists
[pic](Delaware Register of Regulations, Pg. 16)
Chicane (Delaware Register of Regulations, Pg. 16)
A type of horizontal deflection such as a chicane is a curved S-shaped traffic calming measure which slows the traffic by having a slight curve in road, making motorists have to sway a little to follow the road. Normally, three alternating curb extensions are used. (Ewing, Pg. 38). Well-designed chicanes can decrease vehicle speeds and traffic volume.
The purpose of a chicane is to interrupt any single lane of traffic. This is done by offsetting the middle section of neighbouring chicanes by about 2 meters. Increasing the length and reducing the height between chicanes can reduce the strain on emergency and transportation systems, but can also increase the travelling speed of the traffic. In addition, a 1 meter drainage channel is required (Skene, Pg. 4-9, 4-11).
The most important aspect of chicanes is their placement. The location of a chicane must consider all driveways, fire hydrants, and parking areas. According to European guidelines, the alignment of chicanes should shift a minimum of one lane width, and have a deflection of no less than 45 degrees. The purpose of central chicanes is to inhibit the race track effect (Ewing, Pg. 38).
Two-lane chicanes are most effective on wide residential and collector streets. Chicanes must have a clear, direct path between them. A chicane on a two-lane street must have a paved width of 12 meters and a chicane on a one-lane street must have a paved width of 7 meters.
Chicanes can also be landscaped or streetscaped to enhance the neighbourhood’s safety and appearance. Landscaping of chicanes has several considerations: sight distance, cost, climate, and other local regulations. They should also be accepted by the residents and street users of the area.
Normally, Object Markers, Delineation Markers or Bollards with reflective tape are located in the middle of the chicane to help drivers navigate around the chicanes. For one way chicanes, a sign should warn motorists that there is a chicane ahead. A Yield sign as well as a Yield To Oncoming Traffic sign are required in front of two-way one lane chicane to warn motorists of the narrowing road and the possibly of having to yield. Stopping Prohibited signs are also required along the chicane (Skene, Pg. 4-9, 4-11)
(Skene, Pg. 4-10)
Lateral shifts - axial shifts, staggering or jogs
Curb extensions bend the lanes of the road to create a slight twist which produces a lateral shift. Lateral shifts are used frequently in Europe as standard calming measures. Lateral shifts are also used in the United States in cities such as Beaverton and West Palm Beach. Like chicanes, lateral shifts are a useful and cost-effective way to create extra parking and slow traffic (Ewing, Pg. 39). Lateral shifts have a travel speed 8 kph (8 kph) more than a chicane of the same size, making them better suited for main roads (Deleware Register of Regulations, Pg. 563).
Curb Extension [pic]
Extended curb with sidewalk (Regina, SK).
Curb extensions are located at intersections or at mid-block on both sides of the street to decrease the surface of the roadway. Therefore, they decrease the speed of vehicles.
Usually when approaching a curb extension, each lane should be 3 meters wide or if local policy authorizes, 2.5 meters. However, the departing lane must always be 3 meters wide. Mid-block curb extensions require a minimum width of 2.75 meters for each lane. Curb extensions are most useful when they continue past the intersection and in the opposing direction. A 5 meter offset is necessary if curb extensions are used diagonally across from each other at intersection corners.
Curb extensions are 5 to 7 meters in length, except when they act as bus stops. Curb extensions that are used for bus stops have to be able to hold all buses.
Mid-block curb extensions should to also contain room for cross-walks and shifts in elevation; the minimum requirement is 7 meter long.
Finally, design considerations should be made for emergency operations, service vehicles and transit vehicles depending on the communities needs.
Object Markers should be used when there is profound snow accumulation, low visibility of the curb extension and when there is any kind of sharp corner or abrupt curb extension (Skene, Pg. 4-11).
(Skene, Pg. 4-12)
Center island narrowings - mid-block medians, median slow points or median chokers
To narrow a street, an elevated center island should be located in the middle of the street to reduce the amount of roadway surface (Ewing, pg.39). Normally, center island narrowings are about one car length: 1.8 m 20 m wide and 20 feet long. Center islands are most effective in reducing travelling speeds when they are closely spaced or they disrupt large open streets (Delaware Register of Regulations, Pg. 565).
Curb Radius Reduction [pic]
Curb Radius Reduction at intersection (Regina, SK).
The name says it all! Curb Radius Reduction is a reduction of the curb radius at an intersection. Curb radius reduction slows turning motorists and decreases pedestrian crossing distances.
In general, a smaller radius of 3 to 5 meters is needed for passenger vehicles; though this can cause problems with large right turning vehicles. They may infringe on the sidewalk and damage the surrounding area. A hard surfaced material like concrete or extended sidewalks is an alternative to this problem.
No signs are required for curb radius reduction, but signing is required for any repositioning or replacement of pavement markings or other signs. When combining curb radius reduction and curb extensions, Object Markers should be used in cases of profound snow accumulation, low visibility of the curb extension, or where sharp corners or abrupt curb extensions exist.
(Skene, Pg. 4-13)
Neckdowns - nubs, bulbouts, knuckles or intersection narrowing
[pic] (Delaware Register of Regulations, Pg. 17)
Neckdowns are a type of curb extension which decreases the road surface from curb to curb at intersections. The main benefit of neckdowns is that by reducing the curb radius at the corners, the distance a pedestrian must cross is less and the speed of turning vehicles is decreased. Neckdowns simply help make intersections pedestrian friendly (Ewing, Pg. 39).
Chokers - pinch points, mid-block narrowings, mid-block yield points or constrictions
[pic](Delaware Register of Regulations, Pg. 17)
Chokers are another type of mid-block curb extension which narrows the road surface by widening the sidewalk area (Ewing, Pg. 41). Two-lane chokers are typically from curb to curb and have a length of 6 meters. Chokers should not block curb side parking space or driveways. Chokers can be dangerous for cyclists. Bypass lanes for cyclists should be implemented wherever traffic is heavy (Delaware Register of Regulations, Pg. 564).
Straight and angle On-street Parking (Regina, SK.)
The location of on-street parking depends on the type and lay out of the street.
On-street parking can occur on both or either side of the street and therefore decreases the speed of motorists and sometimes traffic volume. One draw back is that on-street parking requires cyclists to use traffic lanes.
The location is the most important aspect of on-street- parking. The location of the on-street parking must consider driveways, fire hydrants, and parking areas. Note that on-street parking must not be used to create temporary curb extensions.
No parking signs are required to regulate parking in areas of minimum pavement width and on streets where parking is only permitted on one side. If curb extensions are combined with on-street parking, signage is required (Skene, Pg. 4-14).
(Skene, Pg. 4-15)
Raised Median Island [pic]
Raised Median Island with landscaping and pedestrian access (Regina, SK).
Lane width needs to be reduced for raised median islands to decrease the travel speed of motorists on a two lane street. Parking should not be allowed across from a raised median island. Stopping is also ban at raised median islands. If a mid-block crosswalk is combined with a raised median island, parking may be permitted if the sight line is an appropriate distance from the crosswalk. Bicycle lanes can be placed beside curbs where parking is not permitted.
The single lane width next to the median island should not exceed 3.5 meters. Any raised median island should be 5 to 7 meters long at an intersection or mid-block. The length should be controlled by the location of the median island to allow access to driveways and other streets. Raised median islands should have a width of at least 1.5 meters for required signage, and a pedestrian area. The geometry of island medians must follow the GDGCR “Geometric Design Guide for Canadian Roads” requirements.
A Keep Right sign is needed to guide traffic to the right of the median. A Stopping Prohibited sign is also required to maintain the necessary pavement widths. For mid-block crosswalks, Pedestrian Crosswalk signs are compulsory. Pavement markings should follow GDGCR and MUTCDC guidelines. Object Markers are voluntary (Skene, Pg 4-14, 4-17).
Traffic Circle - intersection islands [pic]
A Traffic Circle taking the place of 4-way stop signs (Regina, SK).
Traffic circles allow traffic to flow freely through an indirect path at an intersection. This causes motorists to slow down and yield before entering the intersection. Motorists enter the intersection by first turning right and must turn left around the center island and finally right to exit the intersection (Ewing, Pg. 35). Landscaping the inner raised section of the island, is a nice and easy ways to improve the appearance of the intersection. However, the outer portion must be mountable for medium sized vehicles to maintain functionality (Skene, Pg. 4-17).
There are concerns with traffic circles regarding cyclists and pedestrians. A traffic circle can take over the intersection leaving cyclists and pedestrians with no where to cross. The cost is another concern due to the size of a traffic circle and the materials needed to construct and maintain it (Ewing, Pg. 36).
Mini traffic circles were designed in the 1980’s for more manoeuvrability for larger vehicles. Mini traffic circles are less expensive than regular ones (Ewing, Pg. 72).
A traffic circle must be large enough to create an indirect path for it to be effective. Although other shapes can be can used, a circle shape is recommended (Skene, Pg. 4-17). Each traffic circle has specific dimensions according to the size of its intersection. Traffic circles are sloped from the center of the island for good drainage (Ewing, Pg.73). For mini traffic circles, one standard single-unit truck is used to determine its dimensions (Delaware Register of Regulations, Pg. 559).
Traffic Circle sign is needed to demonstrate the difference in horizontal alignment. Yield signs are recommended for all entrances of traffic circles (Skene, Pg. 4-17).
(Skene, Pg. 4-18)
Roundabout with appropriate signage (Regina, SK).
Roundabouts slow traffic by directing it counter clock-wise around an island. However, roundabouts differ from traffic circles because they have a larger radius and they are more effective on higher volume roadways such as arterial and collector streets. According to international procedures, roundabouts have a design speed of about 40 kph (Delaware Register of Regulations Pg. 561). Motorists must yield, and then they must wait until there is a break in traffic before entering the intersection. Roundabouts assign rights-of-way to motorists and reduce the use of all-way stop signs (Ewing, Pg. 37-38).
Standard roundabouts have inner landscaped areas with a radius of 6.4 meters and outer mountable areas of 1.8 meters around the inner area. According to the Delaware Register of Regulations the dimensions of a normal roundabout include: having flaring entry lanes of 3.4 to 4.6 meters at yield lines. The radii of the roundabout should be smaller than the curved made by the motorist. The circulating lanes should be between 1 and 1.2 times larger than the entry lanes. The exit should be larger and straight to let vehicles accelerate as they leave the roundabout (Delaware Register of Regulations Pg .561).
Traffic calming obstructions are any traffic calming devices that intrude onto a roadway to reduce traffic volumes and/or traffic speeds. Landscaping or streetscaping is commonly used to enhance the aesthetics and effectiveness of obstructions. Landscaping can increase driver awareness of the presence of the obstruction and increase public approval of the traffic calming measure. Care must be taken not to reduce visibility to the point of creating a safety hazard when adding landscaping.
Directional Closure - half closure, semi-diverter [pic]
A modified exit-only directional closure preventing entrance onto the street and blocking through traffic (Regina, SK)
A directional closure is formed by the construction of physical barriers blocking off a particular turning lane at an intersection in order to force traffic to travel on certain streets and limit the use of others. The two different types of directional closures are entrance-only and exit-only. The entrance-only closure barricades the right lane of a residential street at the intersection, allowing vehicles traveling on a collector street to turn onto a residential street, while blocking the collector street from the residential street. An exit-only directional closure barricades the left lane of a residential street, allowing vehicles to turn from a residential street onto a collector street, but limiting access to the residential street from the collector street (Skene, Pg. 4-17, 4-19).
Directional closures must be sufficiently long to discourage traffic from bypassing the closure by travelling on the wrong side of the street. In Ft. Lauderdale, FL, a barricade length of 9 m was found to be sufficient in reducing any illegal bypasses of the obstruction.(Ewing, Pg.23) Barricades on exit-only closures should have an angle promoting the direction of the desired turn on the side of the barricade away from the intersection. The exit-only directional closure must also be wide enough so that two vehicles are unable to pass through the street at the point of the barricade at the same time, discouraging any through traffic at the intersection. Since directional closures are most commonly used on two-lane streets, the full single lane closure is generally used. Gaps on the curb side of the obstruction should be considered to accommodate bicycle traffic. The bicycle gaps should be 1.5 to 2m wide, and the adjacent sidewalk curb should be rolled to reduce the risk to cyclists of clipping their pedals.
For an exit-only obstruction, Entry Prohibited and Right or Left Turn Only signs are required to inform approaching traffic of the obstruction. A sign to exclude cyclists from these limitations should be included. An Object Marker should also be placed on the edge of the barrier closest to traffic. On the collector street, One-Way street signs must be placed in order to inform the traffic on that street that no turning onto the residential street is permitted. For entry only closures, a Cul-De-Sac sign should be placed at the beginning of the block containing the closure along with the Entry Prohibited and Checkerboard warning signs.
(Skene, Pg. 4-21)
Diverter - diagonal diverters, full diverters, diagonal road closures
[pic](Delaware Register of Regulations, Pg. 13)
Modified diverter, allowing access through from one direction. (Regina, SK)
Diverters are used to eliminate straight through traffic at an intersection by directing vehicles onto a different street away from the intersection. Diverters are placed diagonally across an intersection and are almost always incorporated with landscaping in the area where the previous intersection was located. Pedestrian and cyclist paths should also be included to allow access to the adjacent street. The paths through the diverter should have some type of vehicle barricade such as bollards to eliminate illegal use of the path. To accommodate the need for emergency vehicle access through the diverter, a lockable or breakaway gate may be used, but in most instances the length of the diverted route is not long enough to justify this.
Diverters should create a turning radius adequate for all vehicles to a maximum turn radius of 7.5m. Parking should be prohibited along a diverter in order to maintain the minimum diverter width of 1.5 m and to maximize the landscaping area. Bicycle paths and bollard spacing is most commonly 1.5 m as well (Skene, Pg. 4-19, 4-23).
Single turn signs should be placed preceding the diverter or star diverter, and parking prohibited signs should be placed along the diverter.
Star diverters are a star shaped obstruction placed in the middle of a four-way intersection in a similar manner to a traffic circle. The shape of the diverter forces vehicles approaching the intersection from any direction to make a right turn. Since the star diverter does not completely close off the intersection there may be problems with drivers going around the point of the star and proceeding directly through the intersection (Ewing, Pg. 23).
(Skene, Pg. 4-22)
Full Closure - cul-de-sac, dead end [pic]
Full closure with streetscaping (Regina, SK)
Full street closures completely eliminate through traffic by blocking the street with various barriers. Barriers used for full closures include landscaped islands, walls, gates, and bollards. Closures are discouraged in the vast majority of cities through-out North America because of the reduced access for emergency vehicles, and the disturbance that the closures cause to the city’s street networks. Other street calming measures should always be considered first (Ewing, Pg 19). Access for cyclists and pedestrians should be included in a full closure barrier.
The end of the closed roadway should be altered into a type of cul-de-sac to allow vehicles to turn around. In order to prevent illegal traffic use, the street closure barrier should have bollards or other landscaped obstacles placed typically at 1.5 m intervals. Pedestrian and bicycle access through the closure should also have a width of 1.5 to 2 m with adjacent rolled curbs for cyclist safety.
A Cul-De-Sac sign should be placed at the entrance to a street with a full closure. A Checkerboard sign should be placed at the road closure to advise road users that the street has no exit.
(Skene, Pg. 4-24)
Intersection Channelization [pic]
Channelized intersection using a median island (Regina, SK).
Channelized intersections help prevent certain movements such as through and left-turn movements in a particular area. The goal of intersection channelization is to prevent motorists from making illegal turns.
The dimensions of a channelized intersection exit vary due to different channel radii and vehicle size. The right-turn radius of the channel should be large enough to prevent left turns and through movements. The island channel should be between 6 m2 and 10 m2 for pedestrian protection.
An Entry Prohibited sign is needed on the channel island. Right or left Turn Only signs are also needed to warn motorist that they are turning into the cross-street. No Left Turn signs should be placed on the cross-street and the end the channel island. Other required signs are one Keep Right sign and an Object Marker which should be placed in the centre of the protected street on the end of the divisional island. An additional Object Marker must be placed at the pointed corner end.
(Skene, Pg. 4-25)
Raised Median through an Intersection
[pic](Delaware Register of Regulations, Pg. 13)
Raised median blocking left turn and through access (Regina, SK).
Short medians in the middle of intersections hinder left turn and straight through movements from residential streets. The median should have sufficient area for pedestrians and should not be located on streets which require primary emergency aid.
The median should be at least 1.5 meters long and be wide enough to provide a minimum of 3.5 meter lane on each side. It should also extend past the intersection to deter motorists from driving around the median and turning left. If there is a crosswalk, the median should be between 5 to 7 meters past the outskirts of the crosswalk, always depending on driveways and road access.
A Keep Right sign and Object Markers should be on each end of the median. There should be a One-Way sign facing both directions in the middle of the protected street. No Stopping signs are usually needed depending on lane widths and municipal policy. Pavement Markings are also required by the MUTCDC (Manual of Uniform Control Devices for Canada) when nearing the median.
(Skene, Pg. 4-27)
Right-In/ Right-out islands are similar to channelized intersections. Their purpose is to prevent straight through movements and left turns.
The Right-In/Right-out islands should be large enough to prevent left-turns and through movements. The island channel should measure between 6 m2 and 10 m2 to protect pedestrians. Depressed curbs and signs should accommodate larger vehicles which frequent the street often.
Two Right-Turns Only signs are needed, one sign in front of the intersection and the other on the island. A Keep Right sign and an Object Marker are necessary at the end of the island. An Object Marker is required at the end of the island facing the right turning lane onto the confined street. An Entry Prohibited sign is necessary on the island in front of the straight through movement. No Left Turn signs should be placed on the far cross-street as well as at the end of the channel island. Right or Left Turn Only signs are needed; the signs should warn motorist that they are turning into the cross-street. All sign regulations should correspond to MUTCDC standards.
(Skene, Pg. 4-28)
Traffic Calming Signs [pic]
Some commonly used traffic calming signs (Delaware Register of Regulations, Pg. 46)
Most of the signs are traditional MUTCDC signs with the exception of the Speed Hump sign and the Traffic Calmed Neighbourhood sign.
Speed Hump Sign
This original speed hump sign should be located prior to the speed hump with the educational tab sign.
Traffic-Calmed Neighbourhood sign
The traffic-calmed neighbourhood sign as well as the supplementary tab sign are now required in all traffic-calmed neighbourhoods (Skene, Pg. 4-23, 4-26, 4-29).
Conversion Table :
|Length |1 ft = 0.3 m |
| |1 in = 2.5 cm |
| |1 in = 25 mm |
|Velocity |1 mph = 1.6 kph |
|Length |ft = feet |
| |in = inch |
| |km = kilometer |
| |m = meter |
| |cm = centimeter |
| |mm = millimeter |
|Velocity |mph = miles per hour |
| |kph = kilometres per hour |
|Acceleration |g = acceleration due to gravity |
Channelization Directed motion of vehicles and/or pedestrians at an intersection through the use of raised median islands and signs.
Chicane A curved S-shaped traffic calming measure which slows the traffic by having a slight curve in road, making motorists have to sway to follow the road. Normally, three alternating curb extensions are used to create a chicane.
Collector Street A street where vehicles have free movement and access.
Curve Horizontal deflection creates a change in direction making motorists turn their vehicles. Vertical deflection creates a change in gradient making motorists ascend the elevated area.
Deflection A physical change in the vertical or horizontal characteristics of the road.
Depressed Curb A concrete curb which has a lowered section to help drainage or pedestrians. It can also be called a drop curb.
Divert Redirect traffic by utilizing physical barriers and/or signs.
GDGCR “Geometric Design Guide for Canadian Roads”
Local Street Residential Street
Measure A traffic regulating device which controls the movement of motorists, cyclists, and pedestrians.
MUTCDC “Manual of Uniform Traffic Control Devices for Canada”: Gives a consistent procedure for proper signage and pavement marking for traffic control devices.
Regulation A policy supported by government.
Rolled Curb A sloped concrete curb.
Sidewalk The continuation of a sidewalk across an intersection. May be raised
Extension or unraised.
Standard Common specifications for traffic calming devices found to be
suitable under normal circumstances
Streetscaping Physically beautifying the area surrounding a traffic calming measure
while aiding the measure itself. Some examples include planters,
benches, and waste receptacles.
Traffic Calming Physical devices that modify motorist behaviour in order to decrease
traffic speed, traffic volume, or both. Traffic calming enhances the
safety of other street users.
Traffic Volume The amount of traffic that travels on a certain roadway in a specific
Ewing, Reid. (1999) Traffic Calming: State of the Practice. Institute of Transportation Engineers. Ch. 1 – 4
Skene, Michael, Project Chair. (1998). Canadian Guide to Neighbourhood Traffic Calming. Transportation Association of Canada. Pg. 3-12, 4-10 – 4-30
Delaware Register of Regulations. ( 2000). Final Regulations: Geometric Design of Traffic Calming Measures. Vol. 4, issue 3. Pg. 561-565
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