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21st Century Operations Using 21st Century Technologies

What Agencies Are Using Low Cost Improvements?

photo of yellow warning sign with a black downward-pointing curving arrow to the left of a black dot to the left of a black upward-pointing curving arrow; this sign is mounted above a sign with the words "20 mph"

Traffic circles were effective in reducing speeds on residential streets in Portland.

Automobile clubs, municipal agencies, and state transportation departments have all applied low cost traffic engineering solutions.

Low cost improvements are another set of tools available to traffic engineers to mitigate increasing traffic congestion and to reduce crashes. They are best viewed as one of a number of strategies that can be employed by the practicing traffic engineer to effectively and efficiently manage traffic. The research conducted for this study found a number of public and private agencies that have adopted low cost traffic engineering solutions as a continuing part of their programs.

City of Portland, Oregon

Traffic circles have been an integral part of the City of Portland's Traffic Management Program for approximately five years. Portland has utilized traffic circles to reduce vehicle speeds and eliminate very fast traffic on local residential streets. Traffic circles are frequently chosen over other devices because they do not divert truly local traffic and do not restrict access to adjacent streets or land uses.

Experience in Portland and other cities in the U.S. and Europe indicates that traffic circles are effective in reducing vehicle speeds and can reduce the number and severity of intersection accidents.

photo of car traveling around traffic circle

Portland has used traffic circles like the one shown above for approximately five years, dramatically reducing multi-vehicle crashes.

An evaluation by the City of Portland to determine the impact of traffic circles and their potential effect on traffic speeds and intersection safety substantiates the finding that traffic circles are successful at reducing the number of vehicles traveling at high speeds (30-35 mph) on residential streets. On many of Portland's residential streets, 15% or more of the vehicles routinely exceeded 35 mph. After traffic circles were installed, vehicles rarely exceed 35 mph. The larger circles (12-foot radius) appear to reduce vehicle speeds more than smaller traffic circle islands. Moreover, the analysis found that traffic circles have dramatically reduced, if not almost eliminated, reported accidents, especially multi-vehicle collisions. The cost to construct each circle ranges from $3,000 to $9,000.

Springfield, Missouri

The Public Works Department of the City of Springfield, Missouri routinely installed and evaluated low cost traffic engineering improvements to correct safety problems at intersections. As presented in Table 2, these treatments range in cost from $150 to $5,000.

The Department of Public Works continues to install and monitor the effectiveness of various intersection improvement strategies and report this information to city management.

Table 2. Springfield, Missouri Intersection Problem Treatments
Problem Description Cost
Poor signal head visibility attributed to side mounted signals Install mast arm to mount signal heads overhead to improve visibility $5,000
Illegal turning-left movements Install lane use signs $150
Poor alignment of overhead flashing signal at four-way-stop controlled intersection Realign signal and relocate "Stop Ahead" sign to improve visibility $300
Crashes by drivers turning left at signalized intersection Install protected phase $1,500
photo of cars stopped at intersection with three overhead traffic signals  photo of two overhead traffic signals at intersection

Treatments used in Springfield included installing a protected phase (left) and overhead signals (right).

AAA Michigan

AAA Michigan selected locations for improvements based on high levels of crashes. Midblock crashes along the studied corridors were insignificant when compared with the crashes at signalized intersections; therefore, midblock crash treatments were not targeted for implementation, and the focus of the effort was placed on improving signalized intersections. The improvements implemented varied by location; however, in general, they were low cost improvements on the order of approximately $30,000 per intersection (Table 3).

Table 3. Selected Intersections Treated as Part of AAA Michigan Program
Intersection City Description Cost Crash Reduction
Seven Mile Road and John R. Road Detroit Approach lanes re-striped to include left turn lanes at the north, south, and eastbound approaches. In addition, an exclusive left-turn phase for the east-west traffic was installed using a three-phase design. Parking was removed for 200 feet of clear sight distance. Signal heads were upgraded from 8-inch to 12-inch signal heads, and all-red intervals of sufficient length were added. $35,200 50%
Seven Mile Road and Ryan Road Detroit Exclusive left turn lanes were installed along with exclusive left turn phases. No roadway widening was required because existing pavement width was available. The traffic signals were upgraded from 8-inch to 12-inch diameter signal heads, and all-red intervals of sufficient length were installed. On-street parking was removed, providing approximately 200 feet of clear sight distance. $36,100 53%
Hubble Road and Puritan Road Detroit Left turn lanes were installed at all approaches. The traffic signals were upgraded from 8-inch to 12-inch diameter signal heads, and all-red intervals of sufficient length were installed. $30,300 64%

Maryland State Highway Administration

The Maryland State Highway Administration (MDSHA) works to improve mobility through non-traditional signal timing improvements (Table 4). With considerable peak period main line traffic flowing to and from Washington D.C., engineers are challenged to maintain traffic flow while providing adequate service to local and side street traffic.

Table 4. Examples of Innovative Low Cost Implementations by Maryland State Highway Administration
Problem Treatment Approximate Cost
Mainline congestion resulting from inadequate storage capacity Two exclusive left turns allowed per cycle $5,000 per intersection
Lengthy delays for minor movements Half-cycle variation $5,000 per intersection
Lengthy mainline queues and congestion Directional lead-lag $5,000 per intersection
Crashes by drivers turning left at signalized intersection Install protected phase $1,500

Signal Timing Improvements

Two turn phases per cycle – In situations where main line peak period flow requires an extended green period, left turn lanes that are not permissive can extend beyond the storage area, causing disruption to main line traffic flow. In these situations, MDSHA has begun allowing for two exclusive left turn lane periods per main line cycle. The lead- and lag-exclusive left turn is activated in the direction of peak period traffic flow. This has proven to be an effective, low cost method to improve mobility. The process requires the controller to be reprogrammed. The total cost is below $5,000, with half for reprogramming the controller and half for engineering assessment of the intersection and potential treatments.

Half-cycle variation – A variation of the "half cycle" is used to decrease delays for minor movements while maintaining traffic flow on the main line. A 3-minute cycle will consist of one long mainline movement, then a side street movement, another short mainline movement, and another side street movement. This variation is useful when developing progression on two consecutive intersections with different cycle lengths. Synchronization software is utilized to assess signal cycles prior to implementation. The innovative signal cycle improves main line traffic flow at a cost of less than $5,000.

Directional lead-lag – At intersections where only exclusive left turns are allowed, MDSHA has begun to use a signal cycle called "directional lead-lag". By utilizing signal synchronization software, the process allows one direction-exclusive left turn and mainline traffic flow during the lead phase, allowing the other direction-exclusive left turn and mainline movement during the lag phase of the green band. Field assessments have shown this to double the duration of green bands, reduce queues, and reduce unnecessary stop time. The innovative signal cycle improves main line traffic flow at a cost of less than $5,000.

Pennsylvania Department of Transportation

The Pennsylvania Department of Transportation (DOT) developed a program of low cost safety improvements as an element of its Safety Management Plan (Table 5). Improvements were targeted at high crash locations. Funds were made available to implement a variety of low cost actions, including the following:

  • pedestrian channelization devices and addition of a 3-second advance for pedestrians at signalized intersections,
  • centerline rumble strips where concentrations of head-on crashes occurred on two-lane highways, and
  • removal or delineation of trees or utility poles where the concentration of crashes involving trees occurs in a set segment of highway.
Table 5. Sample Problems Treated by Pennsylvania DOT
Problem Treatment Approximate Cost
Head-on crashes Centerline rumble strips $5,000 per mile
Fixed objects on roadside
  • Tree delineation utility pole delineation
  • Shoulder rumble strips
  • $90 per pole
  • $3/linear foot
Pedestrian safety 3-second advance for pedestrians at signalized intersections $5,000 per intersection

Centerline milled rumble strips are designed to reduce the incidence of drivers crossing into the opposing travel lane by using the sound and sensation of encroachment across the centerline to alert them. This treatment costs approximately $5,000 per mile and is effective in reducing the frequency of head-on crashes.

photo of raised horizontal strips across yellow centerline in roadway  photo of pedestrian crossing sign on center line in roadway

Pennsylvania DOT used centerline milled rumble strips (left) and pedestrian treatments (right) as elements of its Safety Management Plan.

A variety of low cost pedestrian safety treatments have been applied by the Pennsylvania DOT, including time extensions for pedestrians at signalized intersections to give pedestrians a three-second head start when crossing, installation of "Stop for Pedestrians in Crosswalk" sandwich boards, and exclusive pedestrian phases at intersections with a high level of pedestrian and vehicle crashes.

Pennsylvania DOT has also installed delineation treatments on roadside obstacles, such as utility poles. While these are very inexpensive treatments, they have proven to be effective in reducing fixed-object crashes.

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