National Academies Press: OpenBook

Guidance for the Design and Application of Shoulder and Centerline Rumble Strips (2009)

Chapter: Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research

« Previous: Section 3 - Purpose, Types, and Dimensions of Rumble Strips
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
Page 20
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Suggested Citation:"Section 4 - Review of Completed Shoulder and Centerline Rumble Strip Research." National Academies of Sciences, Engineering, and Medicine. 2009. Guidance for the Design and Application of Shoulder and Centerline Rumble Strips. Washington, DC: The National Academies Press. doi: 10.17226/14323.
×
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16 S E C T I O N 4 This section summarizes the review of completed research on shoulder and centerline rumble strips. This review includes research completed by other agencies prior to and during the course of this research. The information is organized as follows: • Safety impacts of shoulder rumble strips, • Safety impacts of centerline rumble strips, • Operational impacts of centerline rumble strips, • Vehicle dynamics related to vibration and noise stimuli, • Effects of rumble strips on specific types of highway users (i.e., motorists, motorcyclists, and bicyclists), • Pavement performance issues, and • Other potential adverse concerns. A detailed review of the completed rumble strip research is provided in Appendix A. Safety Impacts of Shoulder Rumble Strips Safety evaluations of shoulder rumble strips have been conducted in many states, and in some cases the evaluations included data from multiple states. Table 4 summarizes the results of these safety evaluations, along with results from sev- eral unpublished materials. Table 4 shows the state/location of the evaluation, the type of facility where the rumble strips were installed, the types of collisions included in the analysis, the estimated safety effectiveness of the rumble strip appli- cation, and the type of analysis that was performed (i.e., if it could be determined from the reference material). The following are several key findings: • Most of the studies evaluated the safety effectiveness of shoulder rumble strips installed along freeway facilities. Only a limited number of studies investigated the safety effectiveness of shoulder rumble strips along lower class roadways (i.e., nonfreeways). • Most of the evaluations were limited to those collision types most directly affected by the installation of shoulder rumble strips (i.e., SVROR-type crashes). However, several studies did investigate the safety impact of shoulder rum- ble strips on total crashes. • SVROR crashes were reduced by 10 to 80 percent due to shoulder rumble strips. The simple average percent reduc- tion in SVROR crashes from these studies is 36 percent. • Total crashes were reduced by 13 to 33 percent due to shoul- der rumble strips. The simple average percent reduction in total crashes from these studies is 21 percent. Concerning the safety effectiveness of shoulder rumble strips, NCHRP Report 617: Accident Modification Factors for Traffic Engineering and ITS Improvements (28) summarizes the status of crash reduction factors for a variety of treatments. In prepar- ing NCHRP Report 617, a panel of safety experts assigned a level of predictive certainty to each accident modification factor (AMF) based upon a critical review of the published research. In assigning a single value or values of the safety effectiveness of shoulder rumble strips, the panel only referenced the 1999 study by Griffith (1) and assigned a medium-high level of predic- tive certainty to these estimates. NCHRP Report 617 specifically states that the estimated safety effects are only applicable to free- ways and not other types of roads (i.e., two-lane or multilane roads). Finally, draft chapters of the forthcoming Highway Safety Manual (HSM) include AMFs for shoulder rumble strips for freeways and rural multilane divided highways. The AMFs for freeways are based upon research by Griffith (1) and Perrillo (23), and the AMFs for rural multilane divided highways are based upon research by Carrasco et al. (3). Safety Impacts of Centerline Rumble Strips Table 5 summarizes the results of safety evaluations that quantified the safety effectiveness of centerline rumble strips. Review of Completed Shoulder and Centerline Rumble Strip Research

These safety evaluations suggest that head-on collision fre- quency and rate decreased after installation of the centerline rumble strips. Several key findings are as follows: • Most of the studies evaluated the safety effectiveness of centerline rumble strips installed along rural two-lane roads. Only one study investigated the safety effectiveness of centerline rumble strips along another type of roadway (i.e., rural multilane highways). • Most of the evaluations were limited to those collision types most directly affected by the installation of centerline rumble strips (i.e., head-on or crossover-type crashes). However, several studies did investigate the safety impact of centerline rumble strips on total crashes. • Head-on crashes were reduced by 34 to 95 percent due to centerline rumble strips. The simple average percent reduc- tion in head-on crashes from these studies is 65 percent. Concerning the safety effectiveness of centerline rumble strips, NCHRP Report 617 (28) only referenced the Persaud et al. study (4) when assigning a single value or values of the safety effectiveness of centerline rumble strips and 17 State/location Type of facility Type of collisions targeted Percent decrease (–) or percent increase (+) in target collision frequency from application of shoulder rumble strips (standard deviation) Type of analysis Arizona (16) Interstate SVROR –80% Cross–sectional comparison SVROR –49% California (17) Interstate Total –19% Before–after with comparison sites Connecticut (18) Limited–access roadways SVROR –32% Before–after with comparison sites Fixed object –41% Florida (16) Ran–into–water –31% Naïve before–after SVROR (total) –18% (±6.8%) Freeways SVROR (injury) –13% (±11.7%) SVROR (total) –21.1% (±10.2%) Illinois and California (1) Rural freeways SVROR (injury) –7.3% (±15.5 %) Before–after with marked comparison sites and a comparison group Kansas [unpublished; cited in Stutts (19)] Freeways SVROR –34% Unknown Maine (20) Rural freeways Total Inconclusive Before–after with comparison sites Massachusetts [unpublished; cited in Stutts (19)] nwonknU%24–RORVS Michigan (21 lanoitces–ssorC%93–RORVS) comparison Total –16% Injury –17% SVROR (total) –10% SVROR (injury) –22% Naïve before–after Total –21% Injury –26% SVROR (total) –22% Minnesota (3) Rural multilane divided highways SVROR (injury) –51% Before–after with comparison sites SVROR (total) –13% (8%) Minnesota (2) Rural two–lane roads SVROR (injury) –18% (12%) Before–after EB analysis with a reference group Montana (22) Interstate and primary highways SVROR –14% Before–after with comparison sites New Jersey [unpublished; cited in Stutts (19)] nwonknU%43–RORVS New York (23) Interstate Parkway SVROR –65% to 70% Naïve before–after Pennsylvania (24) Interstate SVROR –60% Naïve before–after Tennessee (25) Interstate SVROR –31% Unknown SVROR –27% Utah (26) Interstate Total –33% Before–after with comparison sites Virginia (27) Rural freeways SVROR –52% Before–after with comparison sites Washington (15 retfa–erofebevïaN%81–latoT) Multistate (16) Rural freeways SVROR –20% Before–after with comparison sites Table 4. Summary of safety benefits attributed to the installation of shoulder rumble strips.

assigned a medium-high level of predictive certainty to these estimates. NCHRP Report 617 also specifically states that the estimated safety effects are only applicable to rural two-lane roads and not other types of roads (i.e., multilane roads). Finally, draft chapters of the forthcoming HSM include AMFs for centerline rumble strips for rural two-lane roads, which strips are based upon research by Persaud et al. (4). Operational Impacts of Centerline Rumble Strips Lateral positioning and vehicle speed are the two measures most often considered when investigating the operational impacts to vehicular traffic due to the presence of centerline rumble strips. In most cases it was found that the installation of centerline rumble strips does impact the lateral positioning 18 State/Location Type of facility Type of collisions targeted Percent decrease (–) or percent increase (+) in target collision frequency from application of centerline rumble strips (95% confidence interval) Type of analysis %24–)latot(no-daeHCalifornia (29) Rural two–lane road %09–)lataf(no-daeH Naïve before– after Head-on –34% Colorado (30) Rural two–lane road %5.63–epiwsediS Naïve before– after %59–no-daeH Drove left of center –60% %31+ODP %4+yrujnI A/NlataF Delaware (31) Rural two–lane road %8–latoT Naïve before– after Massachusetts (32) Rural two–lane roads Head-on Opposite-direction angle Opposite-direction sideswipe SVROR with centerline encounters Inconclusive Before–after with comparison group Total –42% Total (fatal and severe injury) –73% Head-on / opposite- direction sideswipe / SVROR–to–the–left (all severities) –43% Minnesota (33) Rural two–lane roads Head-on / opposite- direction sideswipe / SVROR–to–the–left (fatal and severe injury) 13% Cross– sectional comparison Missouri (34) Rural two–lane roads –erofebevïaN%06–latoT after Nebraska (35) Rural two–lane roads Cross–over crashes –64% Naïve before– after –69.5% Naïve before– after Oregon (36) Rural two– and four–lane highways Cross–over crashes –79.6% Before–after with comparison group )%02–8(%41–latoT )%52–5(%51–yrujnI Frontal/opposite-direction sideswipe (total) –21% (5–37%) Multistate (4) Rural two–lane roads Frontal/opposite-direction sideswipe (injury) –25% (5–45%) Empirical Bayes (EB) before–after Table 5. Summary of safety benefits attributed to installation of centerline rumble strips.

of vehicles and that the presence of centerline rumble strips causes drivers to move further away from the centerline (37–42), but at least one study (33) suggests that centerline rumble strips do not impact the lateral positioning of vehicles. Regarding encroachments, one study (33) suggests that center- line rumble strips reduce the number of encroachments, while another study (39) suggests otherwise. The results of five studies (33,37,39,40,42) suggest that centerline rumble strips do not change vehicle travel speeds, or if a change in vehicle speed does occur, the change is small or minimal. Noyce and Elango (32) concluded, based on driver simu- lation studies, that motorists encountering centerline rumble strips do not always immediately steer their vehicles back to the right toward the intended travel lane. This finding is somewhat counterintuitive and is cause for concern. How- ever, Miles et al. (38) indicate that centerline rumble strips do not significantly change driving behaviors in passing zones nor do they affect the driving environment adversely or induce unsafe driving practices. Vehicle Dynamics Related to Vibration and Noise Stimuli The noise and vibration created by rumble strips is the key feature in their use. Unlike most other visual-based traffic con- trols, rumble strips use noise and vibration to create a response from the driver. To determine optimum rumble strip dimen- sions, numerous studies have been conducted to detect the amount of vibration and noise generated by vehicles as they traverse different types and patterns of rumble strips. Several recent studies (14,43–45) have focused on finding rumble strip dimensions that are a compromise between the alerting properties desirable for motorists and the neg- ative benefits potentially experienced by bicyclists when encountering rumble strips. In general, higher vibration and noise levels generated by rumble strips are desirable to alert inattentive/drowsy motorists. On the other hand, lower vibration levels are desirable for bicyclists so that bicyclists do not experience discomfort and control problems while travers- ing the rumble strips. The more recent studies (14,44,46,47) have also collected vibration and noise data for more types of motor vehicles. It is important to note that the transferability of results, or the ability to compare results between studies, is difficult pri- marily because the vibration data were collected in different ways. For example, Hirasawa et al. (42) measured vibrations at the steering column. Bucko and Khorashadi (14) measured the vibrational properties of the steering wheel. Outcalt (44) mounted accelerometers on the floor of the motor vehicle just behind the driver’s seat at the spot where the floor was welded to the vehicle frame and to the steering wheel. Elefteriadou et al. (45) measured the vertical acceleration and pitch angular acceleration of the body frame of the motor vehicle. Chen (48) evaluated vibration based upon the International Roughness Index (IRI). Tye (49) measured the right front-wheel bounce. The study conducted by Elefteriadou et al. (45) was unique in that it was the only study that utilized simulation modeling to investigate optimum dimensions of rumble strips, and it was the only study that tried to measure the impact of rumble strip patterns on the controllability of a bicycle by using an objective measure of control (i.e., the ability of a bicyclists to ride along a designated path while traversing the rumble strip). Even though numerous studies have been conducted to investigate the optimum dimensions of rumble strips, there is no clear absolute answer to the issue. Several general points that may be concluded are the following: • The sound levels generated by the various rumble strip configurations differ in the various test vehicles. • In general, for milled rumble strips, wider and deeper cuts will generate higher levels of vibration and noise for all types of vehicles because of tire-drop capabilities; however, tire drop is dependent upon the properties of the tire, the speed of the vehicle, and the spacing of the cuts. Effects of Rumble Strips on Specific Types of Highway Users 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. However, shoulder and/or centerline rumble strips may also cause unintended behaviors or may negatively impact certain types of highway users such as motorcyclists and bicyclists. This section summarizes those studies in which participants subjectively rated the impact of rumble strips and, to the extent possible, focuses on the correlation between the alerting prop- erties of the rumble strips (i.e., vibration and sound levels) and the reactions or behaviors of highway users to these stimuli. Several studies investigated the effect that rumble strips have on drivers of passenger cars. In general it is assumed that rumble strips that generate 3 to 15 dBA of noise above the ambient noise level will alert drivers that their vehicles have drifted from the travel lane. Bucko and Khorashadi (14) rated the alerting properties of various sound levels, suggesting that increases in the range of 11 to 13.5 dBA have low to moderate alerting value compared to increases in the range of 16.7 to 19.9 dBA, which have high alerting properties. It is important to note that Bucko and Khorashadi (14) concluded that vibra- tions felt through the steering wheel are negligible in their alerting properties compared to the noise level produced in the passenger compartment. Therefore, when attempting to 19

rate the alerting properties of rumble strips, Bucko and Kho- rashadi (14) only considered noise level. However, research conducted by Hirasawa et al. (42) suggests that both sound and vibration contribute to drivers’ impressions from the rum- ble strips. None of the studies fully investigated the relationship of the alerting properties of rumble strips (i.e., vibration and sound levels) and the reactions or behaviors of drivers of pas- senger cars. The research conducted by O’Hanlon and Kelley (50) in the early 1970s could probably be considered the most comprehensive research that investigated the human factor issues associated with rumble strips; however, O’Hanlon and Kelley did not measure the vibration levels experienced by the drivers, so they too could not investigate the correlation between the alerting properties of rumble strips and drivers’ reactions to these stimuli. [Note: The various studies and documents that report on either the desired noise levels to be generated by rumble strips or the field studies that doc- ument sound level intensities measured in the field alternate between expressing the sound levels in units of dB and dBA. The intensity of sound is measured in units called decibels (dB). Intensity is perceived as loudness. The notation dBA refers to decibels measured on a sound level meter using the A-weighting filter network. Once the A-weighting scale is selected, the meter mimics the way the human ear responds to sound. The A-weighting scale is the most commonly used family of curves relating to the measurement of sound (51,52). For consistency purposes, it is assumed that even when a ref- erence reported a sound level in units of dB, the A-weighting was applied. Therefore, all units of sound level throughout this document are reported in units of dBA, even if the orig- inal reference reported the sound level in units of dB.] Only one study (14) investigated truck drivers’ reactions to rumble strips. The biggest difference between trucks and pas- senger cars is the level of stimuli experienced by truck drivers when traversing rumble strips. Bucko and Khorashadi note that in commercial vehicles, vibrations are dampened consid- erably because of the size and weight of the vehicles. Thus, the alerting properties of the vibration levels are essentially insignificant, so the noise in the passenger compartment of a commercial vehicle generated by rumble strips has a greater effect in alerting the driver than the vibration. Bucko and Khorashadi also note that increases in the sound level generated by rumble strips in the range of 1.88 to 4.72 dBA were consid- ered to have low alerting value and increases in the range of 3.62 to 4.62 dBA were considered to have moderate alerting value. Only a few studies included motorcycles as part of field experiments. The most detailed study on the interaction between motorcyclists and rumble strips was performed by Miller (53), who investigated motorcycle rider behavior on roads with centerline rumble strips. The research included a review of motorcycle crash records, an observational study of motorcyclists on roads with centerline rumble strips, and a closed course field study where 32 motorcyclists navigated across rumble strips. Miller concluded that centerline rumble strips add no measurable risk to motorcyclists. These results are consistent with findings from other studies (14,42). The research conducted by Torbic (54) is the only investiga- tion that truly looked at the correlation between the alerting properties of rumble strips and bicyclists’ reactions to the stim- uli. Torbic concluded that the relationship between whole- body vibration and a bicyclist’s perception of comfort is linear; as vibration increases, comfort decreases. Torbic also con- cluded there is no clear relationship between whole-body vibra- tion and the controllability of a bicycle. This research was also unique in that Torbic developed a methodology for quantify- ing whole-body vibration of bicyclists based upon guidelines in International Standard Organization (ISO) 2631 (55) to assess human response. In the other comprehensive studies that investigated bicyclists’ reactions to rumble strips (14,44,45), bicyclists subjectively rated the comfort and control levels of bicycles while traversing various experimental rumble strip pat- terns, but no correlation was made between the vibration lev- els experienced by the bicyclists and the subjective comfort and control ratings. Finally, a general conclusion that can be drawn from the three most comprehensive studies that included bicy- cle and motor vehicle testing of various rumble strip designs (14,44,45) is that rumble strips providing the greatest amount of stimuli (noise and vibration) to alert an inattentive or drowsy driver also are the most uncomfortable for the bicyclists to tra- verse. Likewise, rumble strips that are the most comfortable for bicyclists generate the least amount of stimuli in a motor vehi- cle to alert an inattentive or drowsy driver. In all three studies, compromises were made when selecting the rumble strip design most compatible for both types of road users. Very few pedestrians encounter rumble strips so, for all practical purposes, rumble strips have an insignificant effect on pedestrians. Pavement Performance Issues Several pavement performance concerns associated with shoulder and centerline rumble strips have been identified. Very little scientific-based research has been conducted to address these concerns, but through observational reports most of the pavement performance concerns appear to be unwarranted. Several maintenance concerns associated with shoulder and centerline rumble strips have been reported. Mainte- nance crews reported concerns that heavy traffic would cause shoulder pavements with rumble strips to deteriorate faster and that the freeze-thaw cycle of water collecting in the grooves would crack the pavement. For the most part, these concerns have been shown to be unfounded. Most trans- portation agencies do advise against installing shoulder rum- 20

ble strips on pavements that are rated as deformed or show high degrees of deformation and/or cracking. Inclement weather also appears to have an insignificant impact on the durability of shoulder rumble strips. Field tests refute concerns about the effects of the freeze-thaw cycle as water collects in the grooves. In fact, field tests show that vibra- tion and the action of wheels passing over the rumble strips knock debris, ice, and water out of the grooves. Snow plow drivers have also noted that they have come to depend on shoulder rumble strips to help them find the edge of the travel lane during heavy snow and other low visibility situations. Shoulder rumble strips may also present a challenge to maintenance and rehabilitation crews when lane closures require traffic to be diverted to the shoulder. For long-term rehabilitation projects involving asphalt shoulders, most agen- cies simply mill a trench around the rumble strips and fill the trench with asphalt. Once construction is complete, the shoul- der can be resurfaced and new rumble strips installed along the new asphalt overlay. Similar to the experience with shoulder rumble strips, sev- eral agencies have expressed concerns about pavement dete- rioration associated with the installation of centerline rumble strips. However, none of these concerns have been validated. The pavement performance issue that has received the most detailed investigation deals with the preparation of rumble strips prior to overlayment of the shoulder surface so that rideability and pavement integrity are not compromised. New Hampshire DOT (NHDOT) conducted research to develop a specification defining materials, sequences, and/or options to perform this operation successfully. Four test sec- tions were prepared in the following manner for evaluation: • Test Section A: Shim and overlay; • Test Section B: Just overlay; • Test Section C: Mill, inlay, and overlay; and • Test Section D: Mill and overlay. Test Sections C and D performed the best, showing no sign of reflection in the area of the former rumble strips, while Test Section A resulted in mild depressions, and Test Section B resulted in pronounced rumble strip reflection. Thus, prepar- ing areas with rumble strips prior to overlayment either by (1) milling, inlaying, and overlaying or by simply (2) milling and overlaying is preferred over the other two preparation options, which would likely result in some degree of reflection in the area of the former rumble strips. Other Potential Concerns This section summarizes potential issues or concerns asso- ciated with shoulder and/or centerline rumble strips that were not previously addressed. Impact of Noise on Nearby Residents A common problem cited by transportation agencies con- cerning the use of rumble strips is noise that disturbs nearby residents (15). However, noise is generated relatively infre- quently by rumble strips placed on the shoulders and on the centerlines of undivided highways. For shoulder and center- line 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 con- tinue to receive complaints from nearby residents. To address these complaints, some agencies have increased the offset of the rumble strip from the edgeline to decrease the incidence of vehicles falsely traversing the rumble strips. Other transporta- tion agencies have completely removed the rumble strips. Another alternative is to construct noise barriers. It has been noted that some residents claim to be able to hear the noise generated from the rumble strips from up to 1.2 mi (2 km) away (56). Studies have also shown that when rumble strips are terminated 656 ft (200 m) prior to residential or urban areas, tolerable noise impacts are experienced; also at a dis- tance of 1,640 ft (500 m), the noise generated from rumble strips is negligible (57). A recent survey to determine the opinions of residents in areas where centerline rumble strips had been placed showed that the majority of residents find the external noise produced from centerline rumble strips acceptable or tolerable and that the potential driver safety outweighed the effect of the external noise (43). Bicycle Issues Most studies that investigated the impact of rumble strips on bicyclists focused on the comfort and control problems that bicyclists may (or may not) experience while traversing rumble strips. However, bicyclists have several other con- cerns associated with rumble strips that have not necessarily been validated or dismissed through research. The severity or extent of these concerns is difficult to assess without the sup- porting research. One concern with shoulder rumble strips is that they may encourage bicyclists to ride in the travel lane in situations where bicyclists would rather ride on the shoulder. Even though rumble strips are typically installed on only about half of the paved shoulder, the remaining area between the outer edge of the rumble strip and the outside edge of the shoulder is often littered with debris. The debris discourages bicyclists from utilizing that area. Therefore, bicyclists may prefer to ride in the travel lane. A possible solution to this dilemma is to move the rumble strip further from the travel lane to provide bicyclists with adequate room to ride between the travel lane and the rumble strip. This, however, decreases the recovery 21

area available to errant motor vehicles. Another possibility is to make the rumble strips narrower. Yet, another possibility is to provide a gap in the rumble strip pattern to allow bicy- clists to cross back and forth from the paved shoulder to the travel lane without having to encounter rumble strips. A general concern with centerline rumble strips is that motorists may not provide sufficient clearance distance be- tween the bicyclist and the motor vehicle when passing a bi- cyclist on a section of roadway with centerline rumble strips. In other words, the centerline rumble strips may force motorists away from the centerline (as has been shown in several studies) closer to bicyclists riding near the outside edge of the travel lane, leaving less distance between a bicyclist and motor vehi- cle during the actual passing maneuver. Another concern is that when motorists encounter centerline rumble strips dur- ing the passing maneuver, the noise generated by the rumble strips may startle bicyclists, which could result in an undesir- able maneuver by the bicyclist. Maintenance Concerns Weather does cause problems with raised rumble strips. Snow plow blades passing over the rumble strips tend to scrape them off the pavement surface, which is why raised rumble strips are usually restricted to areas that do not contend with snow removal. 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 mark- ings installed on centerline rumble strips. This could poten- tially be a problem under nighttime conditions especially if snow, salt, sand, or debris collect in the grooves of the rumble strips. Visibility of pavement markings can also be an issue when rumble strips are installed along the edgeline. Conflicting evidence as to whether this is an actual problem is found in the literature. However, the majority of studies suggest that visibility/retroreflectivity of pavement markings placed over rumble strips (i.e., rumble stripes) is higher com- pared to standard edgeline/centerline pavement markings, particularly during wet-night conditions. Rumble stripes also appear to be more resilient and durable than standard pave- ment markings, particularly in areas with winter maintenance activities. 22

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 641: Guidance for the Design and Application of Shoulder and Centerline Rumble Strips explores the design and application of shoulder and centerline rumble strips as a crash reduction measure, while minimizing adverse effects for motorcyclists, bicyclists, and nearby residents.

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