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Pavement Friction

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Pavement Friction

MAINTENANCE AND OPERATIONS

1. Does HFST promote higher operating speed?

  • HNTB Corporation monitored speeds after an HFST installation for the Florida DOT and found that speeds post-installation were actually lower.

SAFETY

1. Are there any crash modification factors (CMFs) available for HFST?

  • There are few CMFs available related to HFST at this time, but data collection efforts are ongoing.
  • The FHWA Turner-Fairbank Highway Research Center (TFHRC), as part of the Evaluations of Low Cost Safety Improvements Pooled Fund Study, published the report "Evaluation of Pavement Safety Performance," which included some preliminary CMFs.

FAQ – HFST – 2017

 

1. What is a High Friction Surface Treatment (HFST)?

Definition

  • A High Friction Surface Treatment is a cost-effective safety countermeasure in which a polish-resistant aggregate such as calcined (i.e., heat treated) bauxite aggregate is bonded to the pavement surface using a polymer resin binder, significantly enhancing skid resistance and reducing crashes.

Description

Appendix B – Other HFST Potential Locations and Uses

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.

6. Conclusion

With over 28 percent of all highway fatalities in the United States occurring at or near horizontal curves, it is imperative that transportation professionals continue to identify and implement horizontal curve safety improvements. This guide presented a five-step process for identifying and implementing HFST on horizontal curves which can help practitioners direct financial resources to locations with potential for the greatest benefit.

5. Step 5: Estimate Costs and Identify Funding

This section discusses how to estimate HFST implementation costs and potential means of funding the safety improvement.

5.1. Cost

Costs will fluctuate based on choice of aggregate, binder, and application method. Many agencies can find the lowest unit cost when they are able to get two or more contractors to compete for the project.

3. Step 3: Select Aggregate and Binder Materials

HFST improves roadway surface friction by increasing pavement roughness. The treatment is composed of a thin layer of specially engineered, durable, high-friction aggregate bonded to the existing pavement by a thermosetting polymer resin binder as illustrated in Figure 4. The binder locks the aggregate firmly in place, creating an extremely rough, hard, durable surface capable of withstanding everyday roadway demands, such as heavy braking and even snowplowing.

2. Step 2: Conduct Field Verification and Design

Field verification is an important step in determining whether HFST could be implemented, and if implemented, the limits of the HFST installation. Below is a check list of items that may be considered during a field review.