U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
This section includes case study examples where agencies weighed the decision to install CLRS or SRS when there was potential concern for roadway users other than vehicles, nearby residents, and pavement condition. Examples include cases where rumble strips were installed and later removed after working with local residents as well as an economic analysis of systemic rumble strip installation. These examples show the importance of involving local residents, advocacy groups, and rumble strip committees in policy-making and implementation decision-making. Case studies were provided by Michigan Department of Transportation (MDOT), MnDOT, and TxDOT.
Michigan policy indicates that non-freeway SRS should be used on all rural, two-lane, four-lane, and divided trunk lines where the posted speed limit is 55 miles per hour and the paved shoulder is at least 6 feet wide. If safety concerns outweigh other issues, such as noise and bicycle use, non-freeway SRS can be installed on roadways with narrower shoulders. Early on in the expansion of MDOT’s non-freeway rumble strip program (around 2008), MDOT was made aware of concerns from the Amish community in the southwestern part of the State regarding SRS and the effect on their buggies and horses. The horses would not cross the rumble strips, both CLRS and ELRS. As mitigation, when calling for SRS, designers tried placing the rumble strips very close to the edge line rather than the standard 12-inch offset to leave more room between the rumbles and the edge of the paved shoulder. However, the Amish did not like the resulting tight squeeze and used the travel lane. When a vehicle would pass them, they would cross the CLRS, scaring the horses. Along the same line, the horses did not like to cross the rumble strips because the rumble strips made it difficult for them to set their feet down. There was at least one instance of a horse getting hurt because of stepping into the rumble strips.
As a result of these issues, several sections of non-freeway rumble strips were filled-in to accommodate the horses and buggies. Additionally, rumble strips were omitted in some areas for which they were planned. Within a few months of the concerns being raised, MDOT’s design guidance was modified to take these unique road users into account. The guidance now indicates that "in locations where horse-drawn buggies utilize the roadway, do not use shoulder corrugations unless a crash history exists. Document this as a context sensitive design decision. When a correctable crash history does exist, consider using corrugations and widening the shoulder 2 ft to accommodate both."
The expanding use of rumble strips has resulted in changes to how Michigan roadways are constructed and maintained. Due to concerns that cutting CLRS into an asphalt joint could expedite the joint deterioration, the MDOT adopted a joint density specification to ensure the center line pavement was sound. A field visit with FHWA representatives determined that a single chip seal over rumble strips allowed the rumble strips to maintain functionality; however, a double chip seal significantly reduced the effectiveness. MDOT has updated their Special Provisions for chip seals to indicate that when performing a double chip seal only the top layer crosses the rumble strips. Upon finding that microsurfacing treatments essentially nullified rumble strips but still reflected the grooves (which would be hard to line up on for cutting), MDOT updated their Special Provision for microsurfacing to indicate rumble strips should be filled-in with microsurfacing material prior to the surface treatment such that rumble strips can be re-cut afterwards.
Near New Prague on Highway 19, MnDOT installed CLRS in 2014 in compliance with the State Technical Memorandum. Due to frequent hits of these rumble strips, several residents in the vicinity started to send complaints to the District 6 office (located in Rochester, MN). The district responded by investigating the highway and working with the residents to identify the locations that were generating the noise pollution. After determining which locations, the district removed the rumble strips at the identified locations and has since replaced them with an experimental sinusoidal rumble strip that should create less nuisance noise. Since installation, the district has not received any complaints from the residents. The efforts to remove the rumbles and repave the removed areas did consume both time and money by MnDOT Maintenance and Engineering sections. MnDOT did have to pay for the rumble strip contractor to mobilize and cut in the sinusoidal rumble strips on the one section of roadway.
Along the North Shore in Minnesota, Highway 61 closely follows the shore of Lake Superior. In compliance with both the State Technical Memorandum regarding rumble strips, and with the State strategic initiatives to apply systemic safety countermeasures, MnDOT's District 1 (headquartered in Duluth, MN) installed CLRS along the highway in 2013. Approximately 40 miles of CLRS were installed north of Grand Marais under a districtwide CLRS project and 9 miles of CLRS were installed between Two Harbors and Beaver Bay on a mill and overlay project. Shortly after the installation, complaints started to be received from residents and others with lake/vacation homes. The noise created by hitting the rumble strips was creating noise pollution that many near the highway found to be unacceptable. After significant outcry and organization by the local population (the Cook County Board played a very active role), a noise study was conducted to better understand the issue and potential solutions. The noise study had some findings that the noise would carry further and with greater amplification then was initially assumed. With these findings, District 1 management decided to fill-in or remove certain rumble strips that were near residential locations along significant portions of the highway. All told, nearly 46 miles (with the exception of approximately 3.5 miles near the Canadian Border) of rumble strips were filled in to the satisfaction of area residents. Since the removal, very few complaints have been received. The District is looking into the idea of using sinusoidal rumble strips as a potential countermeasure on any future projects. This project helped jump start a MnDOT initiative to find a quiet yet effective rumble strip. As of the summer of 2016, MnDOT has approved a sinusoidal rumble strip that provides internal vibration and acceptable noise levels, while producing very little noticeable external noise.
Highway 14 is a major arterial in southern Minnesota, spanning from South Dakota to Wisconsin. The highway connects farms to population centers and manufacturing and trade hubs, and is considered a part of the Interregional Corridor System. Highway 14 is also a combination of designs, including two-lane highway, high-speed expressway, and full freeway design. In 2012, near Mankato, a two-lane section of the highway was determined to have a statistically significant above-average rate of fatal head-on crashes. As a response to this issue, MnDOT agreed to expand the highway to a four-lane expressway. However, this would not be completed until the 2016-2017 timeframe. Rather than doing nothing during the project initiation and design phases, District 7 (headquartered in Mankato, MN) made the decision to try an interim typical section to prevent or reduce the chances of a fatal crossover crash. The typical section changed from 10-foot shoulders and 12-foot lanes (total 44-foot width paved top) to a typical section of 7-foot shoulder – 11-foot lane – 8-foot buffer (with tube delineators) – 11-foot lane – 7-foot shoulder. The buffer was a double striped yellow line with rumbles, and was on each side of the delineators (see Figure 10 for an example from Bing Streetside). This was completed in October of 2012. The after results, though a small sample size, appear to be promising. Before the application, this 7-mile segment was experiencing an average of one fatal or severe head-on crash per year, and has only had one minor crossover crash since implementation (through 12/31/2015). In the time frame from 2006 to September 2012 (6.75 years), there were 59 crashes of all types, and from November 2012 through the end of 2015 (3 years), there have been 20 crashes, resulting in nearly a 30 percent total crash reduction. On the target crash type (head-on, ROR-left, and sideswipe) the corridor has gone from 20 crashes in the before period (from 2006 to September 2012 – 6.75 years), to only 4 crashes (from November 2012 to December 2015 – 3 years) after; resulting in a nearly 60 percent total target crash reduction. Fatal and serious injury crashes have gone from 6 to 0.
Figure 10. Photograph. Buffer median on Highway 14 from Bing Streetside.(20)
Currently (since 1999), TxDOT requires that rumble strips be used for rural, four-lane or more divided highways with a speed limit greater than 45 miles per hour. Rumble strips on rural, undivided highways are installed based upon a B/C analysis of the crash history at that location. The higher the B/C ratio, the more likely they will be installed.
In 2016, the Texas Traffic Safety Force conducted an economic analysis of installing CLRS and ELRS on 20,000 miles of rural undivided highways with adequate pavement width.(21) Assuming an average installation cost of 18,000 dollars per mile, the total cost of installations was estimated to be 360 million dollars. The CLRS and ELRS installations would target ROR and head-on crashes, with an estimated 170 to 180 lives saved per year and 2,800 to 2,900 crashes prevented per year. With a conservative estimate of a 5-year service life, the potential lives saved over service life was estimated to be 850 to 900 lives. The estimated cumulative benefit for was estimated to be 4.3 billion dollars, resulting in a B/C ratio of 12 dollars for every dollar spent.
The task force recommended installing CLRS and ELRS on rural undivided highways with adequate lane and shoulder widths. Additionally, further installations were noted to be implemented through collaboration between TxDOT districts and the Maintenance and Traffic Operations Divisions.
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