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

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13 S E C T I O N 3 Purpose of Rumble Strips A rumble strip is a raised or grooved pattern placed on the pavement surface of a travel lane or shoulder (15). Rumble strips are intended to provide motorists with an audible and tactile warning that they are approaching a decision point of critical importance to their safety or that their motor vehicles have partially or completely left the travel lane. Noise generated as the motor vehicle tires pass over the rumble strip provides an audible warning to the motorist, while vibration induced in the motor vehicle by the rumble strips provides a tactile warn- ing. Although rumble strips alert motorists of potential deci- sion points or hazards, rumble strips do not identify what type of action is appropriate. Rumble strip applications fall into four general categories: • Shoulder Rumble Strips—Shoulder rumble strips are placed on highway shoulders, outside of the travel lane. In some cases, the rumble strips may be installed along the edge-line of the roadway and may be referred to as edgeline rumble strips or rumble stripes. Shoulder rumble strips are designed primarily to mitigate SVROR-type crashes. On divided highways, shoulder rumble strips may be installed on the right (outside) shoulder and the left (median) shoulder. Figure 2 illustrates a typical shoulder rumble strip installation. • Centerline Rumble Strips—Centerline rumble strips are placed on or near the centerline of the roadway. Centerline rumble strips are designed primarily to mitigate head-on crashes, opposite-direction sideswipe crashes, and to some degree SVROR-to-the-left crashes. Figure 3 illustrates a typical centerline rumble strip installation. • Midlane Rumble Strips—Midlane rumble strips theoret- ically would be placed in the center of the travel lane (Fig- ure 4). Midlane rumble strips so far are a concept that has been discussed, but no actual installations are known. Mid- lane rumble strips have the potential to mitigate both SVROR and crossover type crashes. They have primarily been discussed for use along roads with narrow or non- existent shoulders. • Transverse Rumble Strips—Transverse rumble strips are placed pretty much across the full width of the travel lanes (Figure 5), and their primary purpose is to alert motorists of approaching intersections, toll plazas, horizontal curves, work zones, or any other unexpected conditions. The cur- rent research does not address this type of rumble strip application. Types of Rumble Strips There are four types of rumble strips: milled, rolled, formed, and raised. They differ primarily by the installation method, their shapes, and sizes. Different amounts of vibra- tion and noise levels are produced by each of the four types. Milled rumble strips are currently the prevalent type of rumble strip among transportation agencies. They are easily installed on new or existing asphalt and Portland cement con- crete (PCC) surfaces, and they produce a great amount of noise and vibration. This type of rumble strip is made by a milling machine, which cuts a groove in the pavement surface. Rolled rumble strips must be installed when the con- structed or reconstructed pavement surface is compacted. Grooves are pressed into the hot asphalt surface by a roller with steel pipes welded to the drums. Depressions are created as the roller passes over the hot asphalt surface. Formed, or corrugated, rumble strips are installed along PCC surfaces. Grooves or indentations are formed into the concrete surface during the finishing process. Raised rumble strips are strips of material that adhere to new or existing pavement surfaces. Different materials that have been used include asphalt bars and raised pavement markers. Use of raised rumble strips is usually restricted to warmer climates due to maintenance difficulties resulting from snow removal in the northern climates. Purpose, Types, and Dimensions of Rumble Strips

14 Figure 2. Typical shoulder rumble strip installation. Figure 3. Typical centerline rumble strip installation. Figure 4. Midlane rumble strip concept. Travel Lane Travel Lane Shoulder Centerline Shoulder Rumble Strips Shoulder Not to scale Travel Lane Travel Lane Centerline Rumble Strips Shoulder Centerline Shoulder Not to scale Travel Lane Travel Lane Midlane Rumble Strips Shoulder Centerline Shoulder Not to scale Travel Lane Travel Lane Transverse Rumble Strips Shoulder Centerline Shoulder Not to scale Figure 5. Typical transverse rumble strip installation. Dimensions of Rumble Strips Figure 6 illustrates an application of shoulder rumble strips along the right (outside) shoulder of a roadway. A variety of terms have been used to describe the dimensions of rumble strips. To minimize confusion as to which dimensions are being referred to throughout this report, the following terms are used to describe/define the dimensions as illustrated in Figure 6. • Offset (A): Lateral distance from the edge of the travel way to the inside edge of the rumble strip. • Length (B): Dimension of the rumble strip measured lateral to the travel way. This dimension is sometimes referred to as the transverse width. • Width (C): Dimension of the rumble strip measured par- allel to the travel lane. • Depth (D): Dimension is the vertical distance measured from the top of the pavement surface to the bottom of a rumble strip pattern. This distance refers to the maximum depth of the cut or groove. • Spacing (E): Distance measured between rumble strips patterns. Typically this dimension is measured from the

center of one rumble strip to the center of the adjacent rumble strip, or it could be measured from the beginning of one rumble strip to the beginning of the adjacent rum- ble strip. Typical terms used to describe this dimension are on-center spacing, spacing on-center, center-to-center spacing, or simply “spacing.” • Recovery Area (F): Distance from the inside (i.e., left) edge of the rumble strip to the outside edge of the shoulder. The recovery area can also extend beyond the edge of the shoul- der to the nearest roadside object. • Gap (G): Distance, measured parallel to the roadway, be- tween groups of rumble strip patterns. Gaps are designed primarily to allow bicyclists to navigate to the other side of the rumble strip pattern without having to encounter a rumble strip. • Height (H): This dimension is not depicted in Figure 6, but it refers to the vertical distance measured from the pave- ment surface to the top of a raised rumble strip. This di- mension corresponds to the depth dimension of milled, rolled, and formed rumble strips. • Lateral Clearance (I): Distance from the outside (i.e., right) edge of the rumble strip to the outside edge of the shoulder. This is the portion of the shoulder to the right of the rumble strips available for bicyclists to ride along the shoulder without encountering the rumble strips. The lateral clearance can also be measured to the near- est roadside object rather than the outside edge of the shoulder. • Departure Angle (): Angle at which a motor vehicle de- parts from the roadway. This angle is a function of the steering angle and the curvature of the roadway. Figure 6 illustrates an application of shoulder rumble strips. Essentially, the same terms [i.e., length (B), width (C), depth (D), and spacing (E)] are used to describe the dimen- sions of centerline rumble strips. 15 Figure 6. Design parameters associated with shoulder rumble strips. Travel Lane Centerline Shoulder Edgeline A B C E a a D C Section a-a F G I α Not to scale