High friction surface treatments: a cost-effective strategy that saves lives
As featured in the "APWA Reporter"
Market Development Manager
Each year in the United States, more than 32,000 people die in traffic crashes. According to the Federal Highway Administration (FHWA), these crashes have an estimated economic cost of more than $230 billion. High friction surface treatment (HFST) is a cost-effective technology that dramatically and immediately reduces crashes, injuries and fatalities. According to the Texas Transportation Institute, “…the purpose of a HFST is to make the road more forgiving to drivers by increasing the friction at locations where the demand for friction is great.”
HFST is composed of a polish and abrasion-resistant high friction aggregate that is bonded to the pavement surface using a high strength polymer resin binder. With friction values far exceeding conventional pavement friction, HFST helps motorists maintain better control in dry and wet driving conditions in high-crash locations such as:
- Horizontal curves
- Bridge decks
- Bike lanes
- Bus lanes
- Toll booth entrance ways
- School zones
Hatherly and Young first reported the benefits of HFST in 1976. They reported that the use of high friction bauxite aggregate, in conjunction with a cold installed polymer resin binder, had demonstrated a 31% decrease in crashes at 800 intersections where HFST was applied.
HFST can be applied either manually or mechanically via dispensing vehicles. However, it is generally agreed that mechanical application results in a more uniform and durable surface that is less prone to material failure.
The polymer resin binder is evenly spread over the road surface at an approximate thickness of 50-55 millimeters. Immediately following, the high friction aggregate is spread uniformly over the polymer resin binder. Once the polymer resin binder has cured, which can be just as short as a few hours depending on weather conditions, the excess aggregate is removed with a vacuum sweeper. The recovered aggregate is recycled and reused.
The use of HFST is rapidly increasing across the United States due to its low cost and effectiveness in significantly reducing roadway departure crashes. Empirical data proving accident reduction using HFST in high-accident, site-specific locations is well documented in states such California, Florida, Kansas, Kentucky, Louisiana, Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia and Wisconsin.
The Kentucky Transportation Cabinet (KTC) is conducting a three year statewide safety improvement program using HFST at over 120 locations to reduce roadway departure crashes on horizontal curves. One particular HFST installation in Kentucky reported 55 wet weather and three dry weather crashes over a three-year period prior to the installation of HFST. In the 2½-year period after the HFST installation, the same location had only five wet weather and one dry weather crashes. An official from the KTC said, “This one project paid for all the other projects in the state.” The KTC test, which ends in the summer of 2013, has already shown a total crash reduction across the state of 69%.
The Pennsylvania Department of Transportation (PennDOT) identified a sharp right turn in a rural county as one of their worst crash sites averaging 2.48 crashes per year. The pavement surface friction reading taken by PennDOT before the HFST application was 33. After the HFST, the pavement surface friction reading was over 95. There have been no reported crashes or skid-off-the-road incidents since the HFST application in 2007. The condition of the HFST after four winters of constant snowplowing is excellent with no material failures.
At another high accident location in Bellevue, Washington, HFST was installed on a negative cambered curve that had been the site of 45 crashes in five years. Since the installation of the HFST, there have been no reported crashes. Site-specific HFST applications are durable and long-lasting. The Virginia Transportation Research Council stated, “It is reasonable to expect them to maintain high friction values for 10 years of service.” Further attesting to HFST’s longevity and cost effectiveness, a recent study from the South Carolina Department of Transportation indicated a cost benefit ratio of about 24 to 1 for its HFST installed on a series of high accident curves.
In addition to its primary use as an anti-skid pavement overlay, HFST is also used in two other types of safety-related applications, bridge deck overlays and pavement demarcations.
HFST is used on bridges as a sealant to prevent cracking and deterioration of the bridge deck. The largest and most complex HFST bridge deck overlay application to date was on Louisiana’s Morganza Spillway. On this four-lane bridge over 3.5 miles long, 78,000 gallons of adhesive and over 2,500,000 pounds of high friction aggregate were installed by three automated HFST installation trucks.
Through the use of brightly colored aggregates, HFST has been shown to be a highly effective pavement demarcation approach. HFST with red aggregate was applied to I-66 west of the I-495 near Washington, D.C., to delineate the HOV (X) lanes, which are utilized in both directions during the morning and evening rush hours. This milestone project for the use of a demarcation to direct traffic was a first for both the United States and the Virginia Department of Transportation.
Using 100% recycled green glass as an aggregate, the country’s first green bike lane was installed last year with HFST in Sammamish, Washington, another first in the United States. The green bike lane was funded through the FHWA, which has issued a nationwide memo confirming green as the chosen color for bike lanes.
Classified by the FHWA as a low-cost safety solution, HFST is the only safety solution that does not require driver response. HFST qualifies for 90% safety funding under the federal government’s Highway Safety Improvement Program (HSIP). A formula apportions HSIP funds to state DOTs to administer. Any local government can apply to their state DOT to get funding for a HFST project in their jurisdiction.
Richard Baker can be reached at (804) 213-0335 or firstname.lastname@example.org.
Sources for more information on HFST:
FWHA Every Day Counts Initiative http://www.fhwa.dot.gov/everydaycounts
High Friction Roads