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Section 5: Shoulder Texturing

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Definition

Rumble strips are depressed or raised patterns used to provide auditory and tactile sensations to the driver to call attention to an upcoming change in conditions. Specifically, shoulder texturing is the use of rumble strips along the shoulder as a warning device to alert inattentive drivers that they are leaving the travelway.

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Types of Shoulder Texturing

Milled-in. Milled-in rumble strips are effective types of shoulder texturing at reducing the number of single vehicle run-off-the-road accidents. Milled-in rumble strips are shallow depressions perpendicular to the edge line. Machinery specifically adapted for this type of work is required. A minimum shoulder width of 8 ft [2.4 m] is required for the outside shoulder to be milled. A minimum shoulder width of 4 ft [1.2 m] is required for the inside shoulder to be milled. Milled-in texturing produces sufficient stimuli to alert inattentive drivers, but does not affect the maneuverability capabilities of vehicles.

Rolled-in. Rolled-in strips may produce less noise and vibration than milled-in rumble stripes; however, rolled-in rumble strips are also effective at reducing the number of single vehicle run-off-the-road accidents. Rolled-in rumble strips are produced by half sections of pipe welded on a steel wheel roller at the appropriate spacing and rolled-in during the placement of hot mix asphaltic concrete pavement. Considerations in evaluating rolled-in texturing include 1) placement must be in coordination with other asphaltic concrete pavement construction, and 2) the temperature of the asphaltic concrete pavement is critical for achieving the proper depth without affecting the remaining surface. A minimum shoulder width of 8 ft [2.4 m] is required for the outside shoulder to be treated. A minimum shoulder width or 4 ft [1.2 m] is required for the inside shoulder to be treated.

Traffic Buttons. Traffic buttons placed along the edge line may also be used as shoulder texturing when milled-in or rolled-in texturing is not feasible. Buttons should be limited to roadways where there is insufficient pavement structure or shoulder width to accommodate either of the depressed texturing treatments and where the accident experience justifies the cost for placing and maintaining buttons. Buttons, however, may be used to supplement other shoulder texturing treatments when appropriate. Buttons may not be suitable where snow plows are used.

Raised Profile Thermoplastic Marking. Raised profile thermoplastic markings installed as the edge line may be used as shoulder texturing when rolled-in or milled-in texturing is not feasible. Raised profile thermoplastic markings used as the shoulder texturing treatment should be limited to roadways where there is insufficient pavement structure or shoulder width to accommodate either of the depressed texturing treatments. Raised profile thermoplastic markings, however, may be used to supplement other shoulder treatments, when appropriate.

Jiggle Bars. Jiggle bar tiles placed in a pattern perpendicular to the edge line may also be used as shoulder texturing when rolled-in or milled-in texturing is not feasible. The use of jiggle bars as shoulder texturing is not encouraged due to the level of auditory and tactile sensations caused by the jiggle bars and the high cost of installing the jiggle bars. Also, jiggle bars may not be suitable where snow plows are used. A minimum shoulder width of 8 ft [2.4 m] is required for the outside shoulder to be treated. A minimum shoulder width of 4 ft [1.2 m] is required for the inside shoulder to be treated.

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Roadway Applications of Shoulder Texturing

For rural freeways and rural four-lane or more divided highways, the following guidelines are recommended:

  • Asphaltic Concrete Shoulders: Rumble strips should be installed as part of new construction, reconstruction, and overlay projects on rural four-lane or more controlled and partially controlled access highways with asphaltic concrete shoulders.
  • Portland Cement Shoulders: Rumble strips should be installed as part of new construction and reconstruction projects. If the concrete shoulder will be used in the near future as a permanent travel lane or a travel lane in a work zone, shoulder texturing should not be considered.

For rural four-lane or more undivided and rural two-lane highways, shoulder texturing on asphaltic concrete or portland cement shoulders is not recommended for these facilities except in special cases where a significant number of accidents, by frequency and percentage of total accidents, are run-off-the-road accidents and the installation of rumble strips is determined to be cost beneficial. The accident history, along with consideration of shoulder use by traffic, mail carriers, bicyclists, and/or farm equipment should be evaluated. If the concrete shoulder will be used in the near future as a permanent travel lane or a travel lane in a work zone, shoulder texturing should not be considered.

For urban highways, shoulder texturing on asphaltic concrete or portland cement shoulders is not recommended.

Bicyclists. When installing shoulder treatments, appropriate riding space for bicyclists needs to be a consideration. The standard details for shoulder texturing treatments provide appropriate riding space.

Placement. Rumble strips shall not be placed across exit or entrance ramps, acceleration and deceleration lanes, crossovers, gore areas or intersections with other roadways. Depressed rumble strips (i.e., milled-in or rolled-in) shall not be placed across bridge decks.

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