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TRAFFIC CALMING POLICY REVIEW
Traffic Calming Devices
Voice Your Views & Concerns
After studying the material on this web site, please provide your views, concerns and ideas about the future of traffic calming in Knoxville.
Policy Review Timeline
What is Traffic Calming?
Traffic Calming Devices
Background
Current Practice
Peer City Review
Neighborhood Survey Results
Other Resources
Traffic Calming Home Page
As our community revisits the City of Knoxville's traffic calming policy, a large question is whether it is feasible for the City to resume installation of physical devices. Traffic calming devices are diverse in both their design and purpose, and therefore it is important to keep in mind that these devices are not suited to meet the needs of every street or neighborhood.

Assuming the City resumes installation of physical devices, it should be noted that, from a technical standpoint, physical devices typically are employed only on local streets. Generally, this would exclude busier streets designated to carry higher traffic volumes such as those with double yellow centerlines.

Since physical traffic calming devices may be appropriate for one type of street but not another, it is important to understand the various classifications of streets. Click here to see the list of Roadway Classifications.

Here is a list of traffic calming devices that are appropriate for local residential streets. For each device, there is a description, a brief listing of advantages and disadvantages, and estimated cost per device.

Stop signs and traffic signals are not included in the list below. Click here to see Devices Considered Inappropriate for Traffic Calming Purposes.

CHANNELIZATION ISLANDS OR MODIFIED INTERSECTIONS
Channelization Islands
  • A raised island can force traffic in a particular direction, such as right-turn-only.
  • Advantages: Reduces vehicle speed, reduces through traffic, necessary to enforce changes in priority from one street to another
  • Disadvantages: Can cause confusion regarding priority movements
  • $10,000
  • CHICANES
    Chicanes
  • Curb bulges or planters (usually 3) on alternating sides, forcing motorists to slow down.
  • Advantages: Imposes minimal inconvenience to local traffic, pedestrians have reduced crossing distance, provides large area for landscaping, provides greater visual obstruction, cost of device is limited by length, effective means of changing drivers' initial impression of street by appearing as road closure yet allowing movement, accepted by public as speed control device, aesthetically pleasing, reduces speed without significantly impacting emergency vehicles.
  • Disadvantages: Increases area of landscaping to be maintained by residents, cost is greater than many other devices (best if incorporated into street reconstruction or initial road design), may create opportunities for head on conflicts on narrow streets.
  • Cost depends on street length. Cost to address storm water issues can make this device cost-prohibitive.
  • GATEWAYS
  • Gateways indicate changing road conditions, traffic calming, residential or commercial districts.
  • Advantages: Positive indication of change in environment from arterial road to residential street, reduces entry speed, reduces pedestrian crossing distances, helps give neighborhood a sense of identity, allows neighborhood creativity and participation in design
  • Disadvantages: Maintenance responsibility, must be funded by residents
  • Cost depends on design, construction materials and labor.
  • HORIZONTAL SHIFTS
    Horizontal Shift
  • Lane centerline that curves or shifts
  • Cost depends on street length. Cost to address storm water issues can make this device cost-prohibitive.
  • LANE NARROWINGS, 2 TO 1 LANE
    Lane Narrowings
  • Curb extensions, planters, or centerline traffic islands are used to narrow traffic lanes. Also called "chokers."
  • Advantages: Minor inconvenience to drivers, minimal inconvenience to local traffic, good for pedestrians due to shorter crossing distance, provides space for landscaping, slows traffic without seriously affecting emergency vehicles, effective when used in series, single lane narrowing reduces vehicle speed and through traffic
  • Disadvantages: Only partially effective as visual obstruction, unfriendly to bicyclists unless designed to accommodate them, conflict between opposing drivers arriving simultaneously could create problems
  • $10,000, plus cost to address storm water issues (can make this device cost prohibitive).
  • MEDIAN ISLAND
    Median Island
  • Raised island in the road center (median) narrows the lanes and provides pedestrians with safe place to stop while crossing the road.
  • Advantages: Provides refuge for pedestrians and bicyclists, may improve streetscape if landscaped, provides barrier between lanes of traffic, may produce a limited reduction in vehicle speeds
  • Disadvantages: May reduce sight lines if over landscaped, increase costs for landscaping maintenance, impair access, and encourage wrong-way drivers
  • $10,000
  • PARTIAL OR FULL STREET CLOSURE
    Partial or Full Street Closure
  • Restricts entry/exit to/from neighborhood by either limiting traffic flow directions at intersection or closing street entirely.
  • Advantages: Reduces or eliminates cut-through traffic in at least one direction, provides space for landscaping, can include two-way access for bicycles.
  • Disadvantages: Reduces access for residents, emergency vehicles can be partially or totally inhibited, often controversial, compliance with semi-diverters (partial street closures) is not 100 per cent, may require maintenance if landscaped.
  • $10,000
  • PAVEMENT TREATMENTS
    Pavement Treatments
  • Special pavement markings and textures (cobbles, bricks, etc.) differentiate the roadway from other areas.
  • Advantages: May be aesthetically pleasing, may be used to define pedestrian crossing
  • Disadvantages: Requires increased maintenance
  • $3,000- $5,000
  • SPEED CUSHION
    Speed Cushion
  • Trapezoidal speed humps require passenger vehicles to slow down but do not slow emergency vehicles.
  • Advantages: Reduces vehicle speeds in vicinity of device, self enforcing, relatively inexpensive, do not impact emergency vehicles
  • Disadvantages: May create noise, drivers may increase speed between humps
  • $3,000- $5,000
  • SPEED HUMPS
    Speed Humps
  • These are curved humps, 7-10 cm high and 3-4 meters long.
  • Advantages: Reduces vehicle speeds in vicinity of device, self enforcing, relatively inexpensive
  • Disadvantages: May create noise, can slow emergency vehicles, may impact storm water drainage, drivers may increase speed between humps
  • $3,000- $5,000
  • SPEED TABLES & RAISED CROSSWALKS
    Speed Tables
  • These are ramped surfaces above the roadway, 7-10 cm high and 3-6 meters long, that can provide a level pedestrian crossing.
  • Advantages: Reduces speed, increases safety of pedestrian walkway if installed, can be designed to be aesthetically pleasing
  • Disadvantages: May create noise, can slow emergency vehicles, may impact storm water drainage, drivers may increase speed between humps
  • $3,000- $5,000, plus cost to address storm water issues (can make this device cost prohibitive)
  • RUMBLE STRIPS
  • Low bumps across the road make noise when driven over. These can be applied strips or can be cut into the pavement.
  • Advantages: Relatively inexpensive, creates driver awareness, may reduce speeds
  • Disadvantages: High maintenance, may adversely impact bicyclists, may not reduce vehicle speeds, create noise
  • $500
  • TRAFFIC CIRCLES
    Traffic Circles
  • These are roundabout islands at intersections.
  • Advantages: Reduces speed at intersection approach, provides space for landscaping, low cost maintenance, makes movements more difficult without restricting them
  • Disadvantages: Typically will require additional signage, initial safety issues as drivers adjust, maintenance responsibility if landscaped
  • $10,000
  • WOONERF
    Woonerf
  • Very low speed residential streets with mixed vehicle and pedestrian traffic
  • Advantages: Can provide very safe multiuse streets including pedestrians, bicyclists and motor vehicles
  • Disadvantages: May be very expensive. Cost depends on size of woonerf area.


  • DEVICES CONSIDERED INAPPROPRIATE FOR TRAFFIC CALMING PURPOSES

    The City of Knoxville Engineering Department adheres to standard engineering practices recommended by the Institute of Transportation Engineers (ITE). Under those guidelines, stop signs, traffic signals, speed limit reduction and "children at play" signs are not considered appropriate for traffic calming purposes. To understand ITE's rationale, please see the following resources, as well as the Current Practices page of this web site.

    Stop Signs
  • Controlling Speeds on Residential Streets by Richard Beaubien http://ite.org/traffic/documents/JDA89A37.pdf
  • City of Phoenix Brochure, "Will Stop Signs Slow Traffic on our Street?" http://www.ite.org/traffic/documents/Phoenix/MoreStopSigns.pdf
  • Presentation by City of Knoxville Traffic Engineering
    http://www.cityofknoxville.org/engineering/traffic

    Speed Limit Reduction
  • City of Phoenix Brochure, "Will a Lower Speed Limit Help Reduce Speeding?" http://www.ite.org/traffic/documents/Phoenix/LowerSpeedLimit.pdf

    "Children at Play" Signs
  • City of Phoenix Brochure, "Will 'Children at Play Signs' Help Slow Traffic?" http://www.ite.org/traffic/documents/Phoenix/ChildrenAtPlay.pdf

    Traffic Signals
  • City of Phoenix Brochure, "Will a Traffic Signal Reduce Accidents at our Intersection?" http://www.ite.org/traffic/documents/Phoenix/TrafficSignal.pdf
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