Guidance for the Design and Application of Shoulder and Centerline Rumble Strips (2009) / Chapter Skim
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Appendix A Detailed Literature Review
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• Pavement performance issues • Other potential adverse concerns A.1. Safety Effects of Shoulder Rumble Strips This section presents results from studies on the safety effectiveness of shoulder rumble strip applications.
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conducted another study on shoulder rumble strip applications for Caltrans. To reduce the number of SVROR crashes, rolled rumble strips were installed continuously along the shoulders of 158.5 mi (255 km)
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Thus, SVROR crashes were reduced by 49 percent on the freeway sections where continuous shoulder rumble strips were installed, while SVROR crashes increased by 20 percent on the comparison sites. The decrease in SVROR crashes was found to be statistically significant at the 99 percent confidence level.
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Table A-2 summarizes the accident data from the 11 treatment sites and comparison sites. Annino used a before-after with comparison sites to evaluate the safety benefits of the shoulder rumble strips.
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Because larger sample sizes were obtained from Illinois, more weight was given to the Illinois findings, so based on the Illinois data, Griffith estimated the average safety effectiveness of continuous shoulder rumble strips to be: • On all freeways, an 18.3 percent reduction in total SVROR crashes with a standard deviation of 6.8 percent. • On all freeways, a 13 percent reduction in injury SVROR crashes with a standard deviation of 11.7 percent.
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assessed the safety effectiveness of continuous shoulder rumble strips for Maine DOT based upon previous studies and estimated a 50 percent reduction in sleep related accidents due to the installation of shoulder rumble strips. Approximately, 37 mi (59 km)
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Based upon the limited data, it was not possible to draw any conclusions on the safety effects of continuous shoulder rumble strips installed along selected sections of Maine's Interstate highways. Table A-3.
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(3) examined the safety effect of shoulder rumble strips constructed on rural multilane highways in Minnesota.
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conducted a study to evaluate the safety effectiveness of shoulder rumble strips in preventing single vehicle off-road and rollover crashes (under wet or dry pavement conditions only) on Interstate and primary highways in Montana.
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However, the safety benefits of shoulder rumble strips on primary highways was uncertain. • In general, rumble strips seem to be moderately successful in reducing the occurrence of various situation crashes, most notably those caused by drowsy or inattentive driving.
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of the New York State Thruway by 1996. Both agencies, NYSDOT and NYSTA, collected before and after data to evaluate the safety effectiveness of the continuous shoulder rumble strips installed within the state.
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in length, by May 1992 rumble strips were installed along five more sections of the Turnpike totaling 31 mi (50 km)
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(25) has been installing milled shoulder rumble strips on all of its Interstate resurfacing projects since 1996.
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concluded the following: • Freeways without shoulder rumble strips experience a higher rate of accidents over those highways with shoulder rumble strips. • Highway segments with rumble strips on asphalt shoulders (continuous and near travel lane design)
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(27) performed a three-year before-after safety evaluation of continuous shoulder rumble strips installed along rural freeways in Virginia.
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(16) conducted a before-after safety evaluation of shoulder texture treatments on rural freeways based on data from 11 states (Arizona, California, Florida, Georgia, Mississippi, Nevada, North Carolina, South Carolina, South Dakota, Utah, and Wisconsin)
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"After" data is for textured condition. d "Before" accident data not available with new construction sites.
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continuous shoulder textured treatments
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A.2. Safety Effects of Centerline Rumble Strips This section presents results from studies on the safety effectiveness of centerline rumble strip applications.
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The overall study found benefits of installing centerline rumble strips from reductions in head on and side-swipe collisions in spite of increases in traffic volume after the installation. Outcalt also noted that centerline rumble strips might increase the danger to motorcyclists and bicyclists.
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Minnesota Study Briese (33) conducted a cross-sectional analysis to determine the safety effectiveness of centerline rumble strips on two-lane rural highways.
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Briese stated that the analysis of target crashes based upon fatal and severe injury crashes should not be considered evidence that centerline rumble strips are not effective. Missouri Study Unpublished results of a study conducted by the traffic safety section of the Missouri Department of Transportation (34)
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The posted speed limit was 55 mph (88 km/h) , and the ADT was 18,000 veh/day with centerline rumble strips installed intermittently within the evaluation section.
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(4) conducted a before-after study of the safety effectiveness of centerline rumble strips on two-lane rural highways using data from seven states, including California, Colorado, Delaware, Maryland, Minnesota, Oregon, and Washington.
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Selection of this treatment site was biased as the centerline rumble strips were installed at a location with a crash frequency and severity rate above the statewide average for similar roadway types. The other segment was 10 mi (16 km)
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Therefore, it is reasonable to conclude that the change in vehicle location was due to the presence of the centerline rumble strips. In addition, no statistically significant relationship between vehicle speed and the placement of centerline rumble strips was found.
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also investigated how centerline rumble strips affect lateral positioning of vehicles within the travel lane. Field data were collected at eight locations using a camera trailer.
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One-year after installing centerline rumble strips The field observations consisted of measuring the number of encroachments, vehicle lateral positions, and vehicle speeds traveling in both directions of travel for various traffic situations. The traffic situations included free flow conditions, flow conditions less than five seconds headway, and flow conditions during the presence of on-coming traffic.
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The centerline rumble strips at the study site were rolled in asphalt; however, a recent review in Finland has recommended the future use of milled rumble strips. Using, what appears to be, a naïve before-after analysis, there was no statistically significant change one month and one year after the treatment installation in any of the key areas under investigation.
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used a passenger car driving simulator to determine how drivers react when encountering centerline rumble strips. Although the analysis showed drivers take more time to return to their intended travel lane when encountering centerline rumble strips than compared to two-lane roadway centerline encroachment without rumble strips, the results were not statistically significant.
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Thus, this result indicates that roadway geometry has an influence on the time needed to return to the travel lane when centerline rumble strips are present. Lastly, it was shown that 20 to 40 percent of drivers initially steer left when encountering centerline rumble strips on two-lane roads.
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skip lines with centerline rumble strips.
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Both passenger car and commercial truck variations were driven on milled, rolled and raised rumble strips at speeds of 55 and 70 mph. Among all of the factors investigated, including vehicle speed, vehicle type, surface type and rumble strip dimensions, the geometric dimensions of the rumble strips proved to be the most striking factor at alerting the driver by means of auditory signals.
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Figure A-3 illustrates the difference between the two rumble strip patterns. The comparison consisted of water and debris collection, interior sound and vibration production, the opinions of bicyclists, and the opinions of residents in areas where the rumble strips were installed.
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Differences in Noise Levels for Each Type of Rumble Strips and the Base Level (dBA)
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Dimensions of Rumble Strips Installed at Tomakomai Winter Test Track in Japan (42) Dimension Pattern 1 Pattern 2 Pattern 3 Length 14 in (350 mm)
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A-37 Figure A-5. Sound Versus Driving Speed (42)
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Table A-18 summarizes the rumble strips patterns installed and tested at the Caltrans test facility. Six motor vehicles were used to collect sound and vibration data: • Light Passenger Vehicles − Chevrolet Lumina (1992)
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The steering wheel was instrumented with accelerometers to measure the vibration generated by the rumble strips (Figure A-8)
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− The noise created by rumble strip 1 (rolled) was greater than milled rumble strip 2 and less than rumble strips 3, 4, and 5 (all milled)
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− The average noise created by rumble strip 1 (rolled) was greater than for rumble strips 2 and 3 and less than rumble strips 4 and 5.
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Sound levels generated by the rumble strip patterns were compared to the sound levels generated inside the vehicles on smooth pavement. The four test vehicles included: • 1994 Oldsmobile Cutlass station wagon • 1999 Dodge full sized pickup truck • 2000 GMC minivan • Unloaded tandem axle dump truck
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. In general, rumble strips patterns 5 through 9 had the highest sound levels.
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. Background measurements were taken in the travel lane at each speed to provide a comparison to the vibration measurements while traversing the rumble strips.
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Study In an attempt to find an appropriate pattern for centerline rumble strips, field tests of 12 rumble strip patterns were conducted in Kansas (46)
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Thus, it was theorized that patterns with higher densities produce higher average decibel levels. As for trends in decibel levels owing to rumble strip length, it appeared that the longer rumble strips generally produced higher average decibel levels, but there was no consistency among the longer lengths.
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0.316 0.685 0.373 0.429 0.494 0.346 0.546 0.482 0.490 0.852 – – 91.34 90.73 91.07 92.73 90.48 91.43 92.01 90.03 90.54 92.31 88.21 – 1995 Ford L8000 Dump Truck (GW = 48,000) 0.915 0.263 0.587 0.465 0.440 0.592 0.456 0.433 0.283 0.950 0.445 – 83.50 82.86 83.77 87.47 82.68 84.18 88.77 81.44 84.11 85.29 – – 1991 Chevrolet 2500 Pick-Up Truck 1.194 0.845 0.452 0.796 0.572 0.896 1.242 0.614 0.753 1.117 – – 82.89 80.01 83.48 84.24 79.61 84.65 83.59 79.46 83.75 83.32 79.01 82.86 1993 Pontiac Bonneville Full-Size Passenger Car 0.568 0.312 0.179 0.274 0.150 0.374 0.970 0.371 0.459 0.786 0.703 1.053 87.34 86.22 87.76 89.97 86.57 87.44 89.74 87.75 88.62 88.42 85.60 – 1994 Ford Escort Wagon Compact Passenger Car 0.711 0.351 0.508 0.430 0.083 0.238 0.483 0.465 0.083 0.990 0.390 – 88.33 85.89 85.59 87.77 84.97 86.12 89.49 82.83 84.09 87.83 80.62 82.56 1995 Ford Aerostar Minivan 1.146 0.904 0.612 0.600 0.530 0.668 0.692 0.851 0.604 0.437 1.083 1.255 85.63 81.24 83.80 88.65 80.48 84.22 86.76 79.87 82.82 – – – 1997 Jeep Cherokee Sport Utility Vehicle (SUV)
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. The testing involved continuous and intermittent milled rumble strips of varying depths, from 0.8 to 0.32 in (2 to 8 mm)
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Table A-27. Ranking of Test Configurations Based on Vertical Acceleration (tandem bicycle)
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Three objective measures were collected during the motor vehicle testing at PTI's test track: • vertical acceleration of the body frame • pitch angular acceleration of the body frame • maximum sound level in the passenger compartment Based upon preliminary results of the vibration data, only the maximum sound level in the passenger compartment of the minivan was used to assess the relative effect of the six rumble strip patterns on the dynamics of the minivan. Table A-31 presents the rankings
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As part of the field testing, Chen conducted pavement roughness and sound level tests on three different types of rumble strips: continuous rolled rumble strips on asphalt shoulders, continuous milled rumble strips on asphalt shoulders, and intermittent corrugated rumble strips on concrete shoulders. Data were collected at 112 locations on Interstates 85 and 295 in Virginia under the following conditions: • Testing speed: 55 and 65 mph (88 and 105 km/h)
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As part of the sound level testing, Chen compared the difference in sound levels between driving in the travel lane and driving over the different rumble strips. The sound levels were measured while driving at 65 mph (105 km/h)
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Noise Test Results for a Truck Traversing Various Rumble Strip Patterns (104) Mean noise level (dBA)
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Using the instrumented test vehicle, Tye collected sound, vibration, and handling data for numerous rumble strip designs. Raised rumble strip patterns were tested using plywood rib rumble strips.
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Varying the width of the rumble strip ribs did not produce significantly higher or lower sound levels for any given spacing of ribs. Rumble strips spacings of 3, 4, and 5 ft (0.91, 1.22, and 1.52 m)
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, primarily from a human factors perspective. In most cases, the intended effect of shoulder and centerline rumble strips is to alert inattentive or drowsy drivers of motor vehicles that their vehicles have departed from the travel lane.
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The primary measures of interested included: • Maximum lateral position • Time from lane departure to "steady state" • Velocity at "steady state" • Time since last lane departure • The number of steering wheel corrections per minute • Time to correct action Table A-34. Patterns of Simulated Rumble Strips at VTI (77)
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. • For departures to the left (i.e., centerline rumble strips)
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conducted his research in Colorado, he assumed that if rumble strips generated noise levels 6 dBA above the ambient noise level during normal operations (i.e., while driving the in travel lane) , that this change in noise level would be a "clearly noticeable change" and would be sufficient to alert an inattentive/drowsy driver.
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• Vibrations felt through the steering wheel are negligible in their alerting properties compared to the noise level produced in the passenger compartment. • Although several rumble strip configurations required an additional amount of hand grip strength, none of the rumble strips caused any fishtailing or loss of control of light passenger vehicles.
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high rumble strips were considered to have adequate to good properties. There were good correlations between the sound levels measured by the instrumentation and the loudness experienced by the evaluators.
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Relevant recommendations made by O'Hanlon and Kelly (50) include: • The use of rib or marker shoulder treatments along highways having relatively high incidents of SVROR accidents.
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As part of their centerline rumble strip research, Russell and Rys (36) conducted a survey to determine the driver's perceived effectiveness of several rumble strip patterns and the presence of centerline rumble strips.
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. Miller investigated motorcycle rider behavior on roads with centerline rumble strips.
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The primary objectives of this research were: • To investigate the relationship between whole-body vibration generated by milled rumble strips and bicyclists' perceptions of comfort • To investigate the relationship between whole-body vibration generated by milled rumble strips and the controllability of a bicycle • To identify the conditions that cause bicyclists to experience the highest levels of discomfort and control problems while traversing milled rumble strips Torbic used data gathered during the PennDOT Bicycle-Tolerable Shoulder Rumble Strips project (45) and supplemented it with additional data to evaluate the ride quality of bicycles.
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Bicyclist Subjective Control Ratings Averaged Across Various Factors (14) As part of the bicycle testing conducted in Colorado, 29 bicyclists participated in subjective testing to rate the comfort and controllability of bicycles while traversing 10 rumble strip patterns (Table A-21)
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is the most favorable. Outcalt notes that the trends in Figure A-17 and Table A-36 are similar to the trends in sound levels in the motor vehicles, indicating that rougher rumble strips to bicyclists are louder rumble strips with more vibration felt in a motor vehicle.
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Lower values indicate greater discomfort, while higher values indicate better comfort. Based on the subjective results, the ordered list below ranks the body parts most affected while traversing rumble strips: • Wrists, fingers, and elbows (most uncomfortable)
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But every rider reported that riding on the rumble strips was annoying." Thus, these tests did not support bicyclists' fears that shoulder rumble strips would cause them to lose control of their bicycles. Table A-38.
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A.6. Pavement Performance Issues Several pavement performance concerns associated with shoulder and centerline rumble strips have been identified.
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The pavement performance issue that has received the most detailed investigation deals with preparation of rumble strips prior to overlayment of the shoulder surface so that rideability and/or pavement integrity are not compromised. New Hampshire DOT (NHDOT)
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• Additionally, a parallel line of "reflected" rumble strips was observed in this test section. It is hypothesized that the vibratory roller drum bounces due to the alternating mix thickness in the rumble strip resulted in the indentation of the surface alongside of the original rumble strips.
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For shoulder and centerline rumble strips, noise is generated only by errant motor vehicles, not by every motor vehicle. Although the noise produced by shoulder and centerline rumble strips is intermittent, transportation agencies continue to receive complaints from nearby residents.
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The sound levels generated by the rumble strips were measured approximately 10 ft (3 m) from the pavement edge.
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. A general concern with centerline rumble strips is that motorists may not provide sufficient clearance distance between the bicyclist and the motor vehicle when passing a bicyclist on a section of roadway with centerline rumble strips (56)
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When raised rumble strips get scraped from the pavement surface, a secondary concern is that the material could become a projectile. Visibility/Retroreflectivity of Centerline and Edgeline Pavement Markings Some transportation agencies have reported concerns over the visibility and retroreflectivity of centerline pavement markings installed on centerline rumble strips (32,36)
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pavement marking materials. The study consisted of a side-by-side comparison of standard MDOT edgelines and standard MDOT waterborne paint and glass beads placed on milled shoulder rumble strips.
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Because of the inability to collect sufficient data for wet-night visibility of standard pavement markings, the retroreflectivity of the rumble stripes were incomparable; however, the Lindly and Narci concluded that the values would have been lower for flat pavement markings than for rumble stripes. Table A-42.
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