What Are Low Cost Traffic Engineering Improvements?
Research has confirmed that low cost, shorter-term strategies that utilize shoulders, narrow lanes, regulatory devices, and technology to manage travel and control traffic can increase capacity and improve operations and safety at a particular bottleneck along a congested metropolitan corridor.
Low cost traffic engineering improvement techniques are typically spot applications or are limited to shorter sections of roadway that do not cover an entire length of an arterial corridor. Some of these strategies include pavement markings, static and dynamic signing, roadway lighting, raised medians, curb cuts, roadway geometric changes, or lane controls. These strategies provide the guidance, warning, and control needed for drivers to ensure safe and informed operation through traffic bottlenecks or congested areas.
An understanding of the types of low cost actions that have been implemented is best gained through the examination of several successful programs, including the Automobile Club of Michigan (AAA Michigan); the Traffic Engineering Department of the City of Winston Salem, North Carolina; and the Traffic Engineering Department of the City of Knoxville, Tennessee.
AAA Michigan initiated a program to identify and treat locations in the cities of Detroit and Grand Rapids with frequent crashes. Over the past six years, AAA Michigan examined 253 intersections in Detroit and Grand Rapids and implemented low cost safety improvements at 112 sites. Actions implemented at the intersections included the following:
- implementation of all-red intervals;
- replacement of 8-inch signal heads with 12-inch signal heads;
- relocation of signal heads to improve visibility by realigning two signal heads facing each other, realigning the signal heads over each lane of travel, or mounting the signal heads using box span installations;
- installation of secondary post-mounted signal heads to improve visibility at some locations;
- installation of back plates on traffic signals to improve visibility at some locations;
- installation of left turn lanes through re-striping of approach lanes and exclusive left turn phases, where needed; and
- removal of on-street parking.
Post-implementation crash studies conducted for improvements in Detroit showed a greater than 50% reduction in total crashes and a greater than 60% reduction in total injuries at the treated intersections. A benefit-cost study conducted as part of the project found a 15:1 return for the Detroit intersection improvements and a 16:1 return for the Grand Rapid intersections.
In 1986, the Traffic Engineering Division of the City of Winston Salem, North Carolina began an annual program to locate and treat crash locations and evaluate the results of such treatments. Over time, the program has completed before-and-after studies at 364 locations, adding 40 to 50 new locations each year. As a result, the program has reduced targeted crashes by 49% and total crashes by 13%.
Low cost treatments implemented at high crash locations included the following:
- creating a left turn lane within the confines of an existing roadway,
- adding left turn phases to existing signals,
- replacing "Yield" signs with "Stop" signs at intersections,
- replacing two-way stops with multi-way stops,
- installing traffic signals,
- using bigger and/or better signs,
- installing short segments of center line and stop bars at "Stop" locations,
- installing double-indicating "Stop" signs (adding a left-side sign),
- painting the message "Stop Ahead" and "Stop" on pavement,
- removing signals from late night/early morning programmed flashing operation,
- adding back plates to existing signal installations,
- adding a signal head to an existing display,
- replacing 8-inch signal heads with 12-inch signal heads,
- adding "Signal Ahead" signs,
- installing red "T" displays (two red signal heads mounted horizontally over an amber and green),
- installing an all-red interval, and
- replacing protected/permissive left turn phases with full protected left turn phases.
The City of Knoxville, Tennessee, Traffic Engineering Department has successfully implemented a number of low cost traffic engineering improvements over the years. Examples include the following:
- installing sight distance mirrors where more expensive earthwork to remove the sight distance obstacle is not feasible,
- installing strobe lights in signals to make the public more aware of signals that are present in areas where background lighting is present,
- providing longer all-red intervals in the signal timing where such things as bridge decks interfere with signals,
- placing signal heads to provide a better view of red signals in limited sight-distance-to-signal faces,
- providing narrower lane widths to provide additional lanes,
- providing narrower lane widths to allow for a pedestrian island, and
- providing detector actuated flashers for sight distance problems that would require very expensive earthwork to correct sight distance problem.
Two state agencies in New York, New York State Department of Transportation (NYSDOT) and the New York State Thruway Authority (NYSTA), installed continuous shoulder milled rumble strips during the 1990s. NYSDOT installed approximately 8,000 shoulder-kilometers of continuous shoulder rumble strips along its existing rural interstate highways and parkways throughout the state between 1993 and 1998. During the same period, the NYSTA installed 3,131 shoulder kilometers of rumble strips on 81% of the New York Thruway (3,864 shoulder-kilometers) between 1992 and 1996.
Both agencies evaluated the effectiveness of continuous shoulder rumble strips by collecting data before and after the installation. They both concluded that the installation of the continuous shoulder rumble strips reduced the number of crashes by at least 65% to 70%. Particularly, NYSTA noted that the number of run-off-road crashes was reduced by 88% (557 cases in 1991 versus 74 cases in 1997), and fatalities declined by 95% (17 cases in 1991 versus 1 case in 1997).
With improved manufacturing efficiencies and increased numbers of installations, the cost of purchasing and installing milled rumble strips has dramatically decreased over the years. For example, NYSTA reports that the linear meter cost of a milled rumble strip was $3.63 in 1993 compared to $0.38 in 1996. These costs do not include maintenance and protection of traffic.
Table 1 contains several more examples of low cost traffic engineering improvements that have been implemented across the country. These actions include restriping pavement to provide additional travel lanes, landscaping to remove restrictions to sight distance, and installing improved signage to reduce crashes.
|Barnstead, New Hampshire||Installed warning signs/beacons at intersection of Route 288 and N. Barnstead Rd.|
|Hampton, New Hampshire||Restriped and narrowed lanes on New Hampshire Route 111 to 11 feet to provide wider bike lanes|
|New Hampshire, various locations||Installed and placed driver speed feedback signs at various locations|
|Bow, New Hampshire||Restriping pavement to provide an auxiliary lane to convert an on- and off-ramp into a weave at interchange of I-89 and I-93|
|Orlando, Florida||Removed and landscaped approaches to improve sight distance at first median cut west of John Young Parkway on Town Center Boulevard due to high collision rate related to inadequate sight distance|
|Glenlig, Maryland||Created left turn lanes with striping and a short bulb-out section on Route 32|
|Stuart, Florida||Reduced number of median openings on U.S. Route 1|