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Traffic Calming Program


"Verkehrsberuhigung" is German traffic calming and "means more than making the traffic quiet, it means making surrounding areas better." It is not unusual for a group of citizens to become concerned about speeding in their neighborhood or downtown, and then top lead to the County Commissioners, Town Council, or the local road agency for more speed limit signs, children at play signs and multi-way stop signs. Additional police enforcement is also frequently sought. Unfortunately, such measures can be worse than ineffective. Inappropriate and unwarranted signs tend to be ignored, and may endanger the public by leading to a general disbelief and disregard for valid and needed traffic control devices. Nonetheless, the need to evaluate and consider traffic calming devices and physical changes to reduce average speeds can be a remedy under certain circumstances. Retrofitting existing community streets to reduce vehicular speeds is an option when persistent problems exist. Each problem area needs to be reviewed individually by the Department and a solution needs to be custom designed to fit the particular situation. Although the community may be consulted to provide input, the DPW&T reserves the right to implement or install measures that address critical safety concerns directly attributable to excessive traffic speeds or volumes, even if the generally required citizen support is not received. Likewise, physical measures may be removed or modified if it is determined that the measure is the direct cause of a traffic safety problem.

Traffic calming devices shall be installed within neighborhoods only if ALL of the following justification criteria are met:

  • Receipt and verification of petitions from (65% minimum of) all residents of the street in question, as defined below; and
  • The street in question must have at least 55% of ADT exceeding the posted speed limit* ; and
  • The street in question must have a speed limit of 25 mph; and
  • The street in question must be classified as a local or neighborhood collector, and
  • The street in question is not a culdesac, and
  • The street in question must not be impaired safety-wise or drainage-wise due to the installation of said traffic calming device, and
  • The street in question must be 750 feet or more in uninterrupted length (excluding intersections), and
  • The street in question already has posted speed limit signs.

*Traffic studies (Speed/Volume) will be taken approximately mid-block(s) of the requested zone(s).

Neighborhood Traffic Calming

In the Spring of 2001, the St. Mary's Department of Public Works & Transportation (DPW&T) launched a Neighborhood Traffic Calming Pilot Program, and is designed to provide a process for neighborhoods to identify and address problems related to speeding motorists, excessive traffic volumes, and overall concern for safety on local residential streets. The pilot program involved the use of speed humps at the entrance to the Lexwoods Apartments. The success of the NTCP will depend on neighborhood residents being involved with the decision-making-process pertaining to the overall program, and to initiate projects that are specific to their neighborhoods. Speed bumps are also maintained on Beach Road, Breezy Point Road and Bayview Road.

The NTCP document provides procedures, guidelines and techniques to assist neighborhood residents in carrying out a NTCP project. The DPW&T is responsible for the information contained in the NTCP document and any related revisions or appeals of its contents. Since NTCP is a neighborhood program, we ask that you please coordinate your efforts for traffic calming in your neighborhood with other residents of your neighborhood.

If there is a street segment in your neighborhood that is experiencing traffic related problems and you want it considered as a potential NTCP project, your neighborhood must submit an application or written request to our office, the Department of Public Works & Transportation by June 1, each year. Typically, we prefer to have a level of consensus of at least 65% of the property owners in the 'affected traffic area". The affected traffic area includes the owners of any property where the only ingress and egress requires passage over and/or through the area where a proposed traffic calming device is proposed.

If you have any questions pertaining to the NTCP, please give our Deputy Director a call at (301) 475 4200 ext. 3536 or email us at

Three Levels

Level I measures are passive in nature and include educational methods and special pavement markings. For these measures to be implemented, they must be requested and supported by the neighborhood. Speed Awareness Programs and Neighborhood Speed Watch Programs are typical Level I measures that are normally handled by our County Highways Division.

Level II measures include traffic control devices and physical measures which control access to neighborhoods, change travel patterns, and regulate the flow of traffic through the neighborhood. Prior to implementation, the DPW&T usually requires a petition be signed by the affected residents. Publications include; One-way Streets (not to be implemented on streets wider than 26 feet), Turn Prohibitions (shall not be considered for residential collector streets), Traffic Circles (limited to minor streets with less than 1,000 vehicles per day), Roundabouts (for minor streets where ADT exceeds 1,000 vehicles per day), Chokers (used only in conjunction with circles and roundabouts as they have limited effect on travel speeds and volumes when used alone), Semi-diverters (must have an adequate alternate route for diverted traffic and needs Sheriff enforcement) and Speed Humps.

Level III measures are used solely for the purposes of addressing severe "through" traffic problems. These measures have the greatest detrimental impact on the residents of the neighborhood and should be considered only after all other measures have been shown to be ineffective. In addition to a petition, a formal Public Hearing is required to provide the general public an opportunity to express their concerns, Due to the severe impact on travel patterns, Level III measures should not be considered on residential collector roadways. Full Road Closures are the most effective method, but also the most restrictive and requires establishing a reasonable alternate route. Diagonal Diverters convert intersections into two unconnected streets with sharp turns and should only be used in conjunction with other control devices.

Point System Criteria

The following factors are used to develop a numerical score for each traffic calming request: Road category (classification); Traffic volume (% current ADT is over the desired volume for the roadway); Speed (how many m.p.h. the 85th percentile speed is over the posted speed limit); Traffic accidents (rate per million vehicle miles); presence of an Elementary School or playground on the street; Major pedestrian generators school, library, park, playground, bus stop, stores etc. within ¼ mile of the subject street); Lack of sidewalks (based on the % of the street that does not have sidewalk); Limited sight distance (uncorrectable and extensive limitations receive higher point totals);and Non-local traffic (amount that the ADT is compromised). Scores are used to rate the requested streets according to their prevailing traffic conditions and to determine which level is appropriate for the subject street. A high score, available funding and other factors are used to determine which roadways will proceed to the next phase. Requests will usually be handled in the following prioritized order; school walking route streets, connector or through streets, and the remaining cul-de-sacs or isolated roadways.

Engineering Retrofit

Retrofitting existing residential streets to reduce vehicular speeds is an option when persistent problems exist in a community. Each community's problems need to be reviewed individually by the Department and a solution needs to be custom designed to fit the particular situation. The community will be encouraged to provide input regarding the options used in developing a final solution.

Options for retrofit include:

  1. Roadway Striping In many cases, a center line stripe can be effective in channeling traffic and thereby reducing speeds. There are also other specialized striping techniques that can be used to draw attention to lane markings.
  2. Edge Line Markings... are used to delineate lane widths. Reducing the lane width has the potential for reducing speeds. The area between the edge of the road and the lane marking can then be used for parking in selected situations or as a bike lane.
  3. Traffic Circles... are generally installed in intersections. Because of the need to deflect around the center island, vehicle speeds can be reduced. The Modern Roundabout design is effective for regulating speeds at intersections. For an animated tutorial of how to safely safe navigation through a traffic circle, please visit the State Highway Administration's Traveling Maryland's Roundabouts website.
  4. Chokers and chicanes... physically reduce the width of the road, thereby forcing the driver to reduce the vehicle speed to safely travel through the device.
  5. Flashing Warning Signs... are generally installed at school locations to alert drivers to pedestrian crossings and to reduce speeds in designated school zones.
  6. Rumble Strips... create tire noise and are used primarily to alert drivers to a change in road conditions. They are rarely used in proximity to homes. "
  7. Median or Pedestrian Refuge Islands... are generally used with multilane roadways and can be used to reduce the width of a road, which can regulate speeds and provide improved pedestrian crossing opportunities. Pedestrian crossings are intended to conform to Americans with Disabilities Act (ADA) requirements.
  8. Intersection Modifications Changing the intersection by restricting the through movements, diverting traffic or raising the pavement height can be very effective in regulating vehicular speeds. These changes can also include reducing the corner radius at intersections, which will lower turning speeds.
  9. Roadway Medians... can range in length, width and architectural features. They are effective in reducing the width of the street and reducing the turning radius at intersections.
  10. Speed Humps... are designed to provide an elongated pavement rise that is designed to allow vehicles to travel over them safely at or below the posted speed. After pilot testing these devices, the county has decided not to use them for traffic calming on a routine basis. This option will be considered only in extremely limited situations and requires specific written authorization by the Director of Public Works and notification to the County Administrator. The cost of installing proposed speed humps ranges for each location. Please contact this office for the expected cost by emailing Speed Humps vs. Speed Bumps
  11. Redesign of Streets In limited instances, residential streets will be subject to reconstruction primarily through the Capital Budget. In these circumstances, there will be opportunity to modify the geometry to reduce vehicular speeds.
  12. Other Traffic Calming Devices There are some other potential traffic calming concepts that could be used to reduce vehicle speeds. Examples include streetscape additions and landscaping. These options will be reviewed on a selective basis.

In order to implement the retrofit program, the following guidelines will apply:

Low Volume Local Roads - For these roadways, which do not have through movements, an education strategy is recommended. Enhanced law enforcement and engineering retrofit would not be used in these locations. Low volume roads would be less than 1000 ADT.

Local Roads and Minor Collectors - For these roadways, which are through streets or have ADT's greater than 1200 vehicles, all of the traffic calming strategies can be employed.

In order for an engineering retrofit to be considered, the prevailing speed (85th percentile) shall be measured in excess of 10 mph over the posted speed limit. When this determination is made, the Department will do an analysis and present a plan of action to the community. The plan may consist of one or more of the retrofit options. After citizen review and community association approval of the plan, the Director will authorize implementation of the plan consistent with the available budget resources.

Major Collector Roads - The primary emphasis for speed control will be enforcement and education. In circumstances where problems continue, retrofits will be considered. Edge markings, roundabouts, chokers, intersection modifications, roadway medians and striping are the principal options for consideration. In unusual circumstances, other options can be considered. The Department will present a plan for citizen review and community association approval. After review and approval by the community, the Director will authorize implementation of the plan consistent with available budget resources.

Arterial Roads - Due to the nature and function of these roadways, traffic enforcement will be the primary method for speed control. However, in some cases traffic calming may still be needed. In these situations, retrofits will be done as a Capital Project.

School Zones - All options will be considered for controlling speeds in school zones. If these alternatives are not successful, speed humps will be considered for traffic calming on local and collector County streets.

Questions and Answers about Speed Humps

Why do we have speed humps?

Speeding on residential streets is a common complaint of concerned citizens. Although enforcement of speed limits by police departments is an effective means of reducing speeds, limited resources do not allow such enforcement on a regular and permanent basis. Research has shown that speed humps are an effective approach to slowing down traffic on residential streets.

What is a speed hump and how is it different from a speed bump?

A speed hump is a gradual rise and fall of the pavement surface along the roadway extending across the pavement width. Generally, speed humps used on residential streets are 12 to 22 feet long with a maximum height of 3 to 4 inches. Speed "humps" are different from speed "bumps", which are seen in many private parking lots. A speed bump is abrupt, having a height of 3 to 4 inches over a length of 1 to 3 feet. Speed bumps cause most vehicles to slow down to almost a stop to go over it. Speed humps, on the other hand, are designed so most vehicles can go over them at 20 mph without causing driver discomfort.

How are speed humps effective in controlling speeds?

Speed humps cause a gentle vehicle rocking motion that causes driver discomfort, thus resulting in most vehicles slowing down to 20 mph at each hump. Speed humps cause a gentle vehicle rocking motion that causes driver discomfort, thus resulting in most vehicles slowing down to 20 mph at each bump. Depending upon street geometry, speed humps are placed every 600 to 800 feet. Speed humps have the advantage of being self-enforcing. They are sometimes referred to as "sleeping police officers".

What will happen if I go over speed humps at high speeds?

At high speeds a speed hump can cause significant driver discomfort. At such speeds it can act as a bump and jolt the vehicle's suspension and its occupants or cargo.

Do speed humps reduce cut-through traffic?

The primary purpose of speed humps is to reduce the speeds of vehicles traveling along a roadway. Traffic diversion due to speed humps is a side effect which may or may not result. A possible disadvantage of speed humps is that motorists may avoid the speed humps by using other nearby streets in the area.

How is a driver warned of the presence of speed humps?

On any street with speed humps, warning signs are placed before the beginning of each series of humps and at each hump. These signs also indicate the speed at which drivers are advised to travel over the hump. To be properly visible, the speed hump is marked with special markings.

Can speed humps be placed on any street?

Speed humps are placed only on residential streets with not more than two lanes and with a speed limit of 30 mph or less. For safety reasons, speed humps are not installed within sections which are curved or where the street slopes uphill/downhill are over 8%.

Speed humps are not typically installed on streets where emergency facilities are located. The Department of Public Works and Transportation communicates with the St. Mary's Fire Department and Emergency Medical Services to ensure that the speed humps will not greatly impact their services. Increases in response time of approximately 8-10 seconds per hump may exist with the installation of speed humps.

What are the different types of speed humps?

There are several speed hump designs that can be utilized. In St. Mary's County, the flat-topped speed hump, which is 22 feet long and 3.5 inches high is the preferred alternative.