2018-114 Traffic CalmingDate: August 31, 2018 Report No. 2018-114
INFORMAL STAFF REPORT
TO MAYOR AND CITY COUNCIL
SUBJECT:
Neighborhood Traffic Management Measures – Traffic Calming
BACKGROUND:
Traffic calming measures are mainly used to address speeding and high cut-through traffic
volumes on neighborhood streets. These issues can create an atmosphere that can be considered
threatening to non-motorists. High cut-through volumes become an increased concern when
larger commercial vehicles are involved. Along with the additional amount of traffic generated
within the neighborhood, cut-through motorists are often perceived as driving faster than local
motorists. By addressing high speeds and cut-through volumes, traffic calming can increase both
the real and perceived safety of pedestrians and bicyclists, and improve the quality of life within
a neighborhood. Because traffic calming measures have the potential to create controversy, their
installation often occurs as the final step of a three-step process referred to as the “three E’s”
(education, enforcement, and engineering).
Education:
Communities with educational programs seek to remind speeding drivers of the negative effects
of their actions, often by stressing that the community’s children are the most at risk. Educational
campaigns may use brochures or neighborhood newsletters to spread this message. Newsletters
may also contain information on speeding fines (particularly in school zones), pedestrian and
bicycle safety tips, and information on average speeds in a neighborhood.
Enforcement:
Enforcement involves a more intensive police presence and a greater allocation of time to
enforcing the speed limit in a particular neighborhood. Unfortunately, it is often not practicable
to maintain a police presence at the level needed to permanently lower speeds. However,
consistent visible enforcement does lead to respect of the speed limit by motorists.
Engineering:
Engineering includes, but is not limited to, traffic calming measures. It can also include the use
of signs and pavement markings to obtain the desired effect. Prior to installing traffic calming
measures on local or collector streets, traffic conditions on adjacent arterial streets should be
investigated to determine if operational deficiencies are contributing to the identified traffic
concerns. In addition, when the use of traffic calming measures may divert large volumes of
traffic from local streets, the effects on adjacent roadways should be addressed.
Date: August 31, 2018 Report No. 2018-114
Below are the steps the City currently follows when a traffic calming request is made by a
resident:
Assessment of the resident request
Collect and compile supporting data
o Identification of project area
o Review of street classification and land use
o Determination of eligibility
Average Daily Traffic (ADT) – 1000 ADT or 100 peak hour vehicles
Speeding survey – 85th percentile speed more than 5 mph above the speed
limit
Cut-through – 40% more for peak hour or minimum 100 cut-through trips
Traffic Calming Plan Development
Neighborhood Meeting – Approval of traffic calming concept
Funding the Project
Engineering Design
Construction
Evaluation of Effectiveness
Based on the above process, if a project is not eligible for traffic calming (e.g. 85th percentile
speed on a particular street is less than the posted speed limit), then the remaining steps are not
carried out and the citizen is notified.
Selecting Potential Traffic Calming Measures:
The selection of traffic calming measures is based on:
1. The potential of a particular measure to address the issue.
2. The type of roadway.
3. Actual site conditions.
Specific measures have been grouped into four categories based on the means by which they
reduce volumes or speeds. The following is a description of the categories:
Horizontal Deflection – refers to two types of traffic calming measures. The first type hinders
the driver’s ability to drive in a straight line by creating a horizontal shift in the roadway. This
shift forces drivers to slow their vehicles in order to safely navigate. The second type of
horizontal deflection measure is designed to narrow the width of the travel lane. Doing so
reduces the usable surface of the roadway causing drivers to slow their vehicles to maintain an
acceptable level of comfort. Although horizontal deflection measures are mainly used to address
speed concerns, applications that narrow the travel lane can improve pedestrian safety by
reducing the width of the crossing. Horizontal deflection measures may also have the secondary
effect of reducing volumes; however, the effects will typically be minor.
Vertical Deflection – refers to traffic calming measures that create a change in the height of the
roadway. When designed properly, vehicles must slow down over these measures in order to
Date: August 31, 2018 Report No. 2018-114
maintain the safety of the vehicle and avoid unpleasant bumping sensations. As with horizontal
deflection measures, vertical deflection measures are mainly used to reduce vehicle speeds, with
minimal impact to traffic volume. Vertical deflection measures can also be used to improve the
safety of pedestrian crossings.
Physical Obstruction – refers to measures that prevent particular vehicle movements, thereby
discouraging or eliminating cut-through traffic. The overall traffic volume reduction depends
upon the nature of the traffic calming measure and the number of movements obstructed.
Signs and Pavement Markings – can be used as traffic calming measures that regulate traffic
movements in lieu of physical changes to the roadway. In certain applications, these measures
may produce the same effect as the physical traffic calming measures.
Aside from their primary function of reducing speeds or volumes, the large majority of measures
also have the ability to reduce issues between motorists and pedestrians, bicyclists, and other
vehicles. In addition, well designed and landscaped traffic calming measures can enhance a
neighborhood’s appearance and quality of life for residents.
Common Varieties of Traffic Calming Measures
Below is a list of commonly used traffic calming measures:
Horizontal Deflection Curb extension / bulb-out Areas of expanded curbing that extend across a parking lane and may narrow a travel lane.
Chicane Series of 3 bulb-outs, staggered at mid-block locations on alternating sides of the street.
Gateway Entrance treatment, typically using physical and textural changes, that
provides identity to an area.
On-street parking Provision of on-street parking that reduces roadway width.
Raised median island Narrow islands, at mid-block or intersections, between travel lanes with breaks in landscaping and curbing for pedestrians.
Traffic circle Raised island in the center of an intersection that requires vehicles to travel
counterclockwise around the circle.
Vertical Deflection Speed hump Raised humps in the roadway, typically 3 inches high with a 12 or 22-foot travel length.
Speed Cushion Series of three to four cushions spaced across the roadway width that
permits wide axle emergency vehicles to pass without slowing down.
Raised crosswalk Marked pedestrian crossings elevated 3 to 6 inches above street grade at intersections or mid-block. Raised intersection Intersections, including crosswalks, raised 3 to 6 inches above street grade.
Physical Obstruction
Semi-diverter Directional closure created by physically blocking half the street.
Diagonal diverter Physical barrier placed diagonally across a four-way intersection to create
two unconnected intersections.
Date: August 31, 2018 Report No. 2018-114
Right-in / right-out island The use of raised islands to prevent left turns and through movements, to and from side streets, at intersections with major streets.
Raised median through
intersection
Median barrier through an intersection that discourages through traffic in a
residential area by restricting movements.
Street closure The use of a cul-de-sac to close a roadway by extending a physical barrier across the entire width, obstructing all traffic movements.
The table below depicts the effectiveness of each traffic calming measure in addressing volume
and speeding problems. The actual effectiveness of any traffic calming device is unique to the
application and the location.
Effect of Traffic Calming Measures:
Date: August 31, 2018 Report No. 2018-114
CONCLUSION:
As the City of Denton continues to grow, neighborhood traffic issues are a major concern for
residents in several subdivisions throughout the community. As discussed in the report, staff
follows a process to assess the traffic related issues by using one of the various traffic calming
options after reviewing and tailoring it to specific neighborhood streets to address the most
common traffic concerns such as speeding and cut-through traffic.
Staff will begin work with the Public Affairs to develop a Traffic Calming Handbook (TCH) that
will provide additional details and design specifications for the commonly used traffic calming
measures. Once completed, the TCH will be presented to the Traffic Safety Committee and
subsequently to the City Council.
STAFF CONTACT:
Pritam Deshmukh, P.E.
City Traffic Engineer
(940) 349-7710
Pritam.Deshmukh@cityofdenton.com