U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
HFST is an appropriate safety countermeasure for locations where friction demand is an issue, other than horizontal curves. Such locations typically requiring large changes in tangent or lateral (centrifugal) acceleration. HFST is a cost-effective countermeasure for these locations because it enhances pavement friction in critical braking or cornering maneuvers. Several States have emphasized HFST success at the following locations.
Specific highway locations, on- and off-ramps, transition lanes, and tolling areas are subject to large speed differentials and changes in acceleration.
High-speed signalized intersections exhibit greater longitudinal force friction on approaching vehicles that are decelerating for a red signal indication and/or turn maneuvers. Increasing friction at these locations is especially important for those with sight distance deficiencies as perceived stopping distance may be inadequate.
Bridge decks tend to polish and wear more quickly due to vertical and lateral forces as vehicles bounce or skip from uneven grades on the bridge approach slab.
Steep vertical grades can be challenging for large commercial vehicles traveling up or down the grade. Areas where pavement friction demands for passenger cars are met might be insufficient for large commercial vehicles.
Environmental restrictions at any of the above locations could hinder countermeasure development. HFST is ideal for environmental restricted locations because the treatment is only applied between existing pavement edges and does not require disturbances to surrounding ground.
Excessive braking at these locations due to speed differentials, sharp curves, and intersection approaches can prematurely polish pavement surfaces, reducing the pavement friction. In such instances, the reduced friction can contribute to vehicles losing control or skidding when they speed, turn abruptly, or brake excessively, particularly during wet conditions. Reduced friction levels also increase a vehicle's required stopping distance, thereby affecting the likelihood of a collision.
HFST has also proven to be an effective treatment at approaches to railroad crossings, schools, and trail crossings. In addition, HFST has been used to delineate and improve traction on bicycle lanes. Since durability is typically not an issue, the treatment is often installed using a dyed aggregate such as glass, instead of calcined bauxite, which clearly delineates the bicycle lane from the motor-vehicle lanes. It also provides a smoother riding surface and improved friction with no negative safety effects.44
There are scenarios for which HFST is not ideal. Some States have indicated that they do not apply HFST on Interstates where heavy trucks frequently use chains in winter because this depletes the life of HFST significantly.45 Other States have found that applying a double layer of HFST at such locations can help minimize the effect of the chains.46
44 FHWA's High Friction Surface Treatments Frequently Asked Questions. Publication No. FHWA-CAI-14-019. [ Return to note 44. ]
45 Interview with Darrell Chambers and Robert Peterson, California Department of Transportation, conducted on November 25, 2014. [ Return to note 45. ]
46 FHWA's High Friction Surface Treatments Frequently Asked Questions. Publication No. FHWA-CAI-14-019. [ Return to note 46. ]
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