ATSSA HFTS 2013 Frank Julian
High Friction Surface Treatments Frank Julian Federal Highway Administration
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
What is a High Friction Surface Treatment? • High Friction Surface Treatments (HFST) are pavement surfacing systems with exceptional skid‐ resistant properties that are not typically acquired by conventional materials • Generally proprietary resin‐based products and processes • Guidelines from the British Board of Agrément (BBA)“…defined as having a minimum skid resistance value (SRV) of 65 measured using the portable Skid‐Resistance Tester as defined in TRL Report 176: Appendix E.”
HFST Aggregates – Generally calcined bauxite or slags with high PSV, but flint, granite, and other materials have also been used – Generally 3‐4 mm maximum size Bauxite
Flint
Granite
HFST Binder Materials • Binder system (proprietary blends) – Bitumen‐extended epoxy resins – Epoxy‐resin – Polyester‐resin – Polyurethane‐resin – Acrylic‐resin
HFST Installation • Manually – Manual mixing of epoxy material – Manual application of epoxy with squeegee – Hand broadcast and distribution of aggregate – Production rates: 200‐500+ SY/hr.
HFST Installation • Automated (machine‐aided) – Machine mixing and application of epoxy (limited hand/squeegee work) – Machine broadcast/application of aggregate – Production rates up to 2,300 SY/hr.
HFST Finished Product
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
Roadway Departure Risk Strategy Keep Vehicles on Roadway Reduce Likelihood of Crashes Minimize Severity
Roadway Departure Crashes 2010 Nationwide Fatal Crashes 30,196 Fatal Crashes 15,786 Roadway Departures Source: NHTSA FARS
Roadway Departure Crash (RwD) - A non-intersection crash in which a vehicle crosses an edge line, a centerline, or otherwise leaves the traveled way.
FHWA Roadway Departure Strategic Plan RwD Fatalities by Most Harmful Event (FARS 2007-2009) 4,156
Overturn Opposite Direction Trees, Shrubs
18,530 Signs, utility poles, traffic signals
3,694
Other Fixed Object Barriers
11,452 14,374
Embankments, Ditches, Boulder, Snowbank Other
Roadway Departure Fatalities Most Harmful Event (FARS 2007-2009) Nearly ¾ of Roadway Departure Fatalities are from 3 crash types.
31% Overturn Opposite Direction Trees, Shrubs
19% 24%
Roadway Departure Fatalities Most Harmful Event (FARS 2007-2009)
45% in HC Overturn Opposite Direction Trees, Shrubs
48% in HC 36% in HC
Fatal Horizontal Curve Crashes
72%
Horizontal Curves and Safety 6.7 7
Average crash rates for horizontal curves is about 3 times that of tangent segments
6
Crashes/km
5 4 3
2.21
2 1 0
Tangent Segments
Curves and Transitions
Source: Glennon, et al, 1985 study for FHWA
Strategies for Reducing Crashes (Where Can HFST Benefit Safety?) 1. Horizontal curves 2. Approach to intersections 3. Grades When the pavement has:
Marginal friction effected by weather Low friction Friction values not compatible with approach speeds and geometrics (friction demand)
Skid related crashes are determined by many roadway factors: Weather Conditions Friction Demand Road Geometry Vehicle Speeds Traffic Characteristics Driver Actions Source NCHRP 108
Conceptual Relationship Between Friction Demand, Speed and Friction Availability
Source NCHRP 108
AASHTO Horizontal Curve Design Model a
a
e = superelevation f = side friction factor V = design speed (mph) R = radius of curve (ft)
e+f = V2/15 R
Side Friction Demand, g Relationship between curve speed and side friction demand for two radii
Source TRR 2075
What about Friction Demand? In an existing curve the following is known: • superelevation, • radius • curve approach speed
Solve for friction demand: Fs = V2 ‐ e 15R
Basis for AASHTO Curve Design Model Is Driver Comfort Although the curve design policy stems from the laws of mechanics, the values used in design depend on practical limits and factors determined empirically over the range of variables involved.
Improving Friction to Keep Vehicles on the Roadway AASHTO Design assumes vehicles: do not exceed the design speed traverse the curve following a constant radius.
Likelihood of skidding increases when these assumptions are violated. Several studies have shown that under real world conditions both of these assumption are violated. Source NCHRP 500 Volume 7
Speeding- Related Crash Typology When crash types were examined for these drivers excessively speeding, researchers found that speeding was the leading cause of single‐driver right or left roadside departure with traction loss and the third leading cause of head‐on crashes. …primarily on curves, at night, on local or collector roadways, and during clear weather.
Truck Operations on Curves Skidding trucks may lead to overturn Friction demand varies per tire Trucks on downgrade curves generate greater lateral friction demand Margin of safety for ‘f’ is lower for trucks Trucks with high centers of gravity may overturn before losing control due to skidding Source NCHRP 505
“Where practical, the maximum side friction factors used in design should be conservative for dry pavements and should provide an ample margin of safety against skidding on pavements that are wet as well as ice or snow covered. The need to provide skid‐resistant pavement surfacing for these conditions cannot be overemphasized because superimposed on the frictional demands resulting from roadway geometry are those that result from driving maneuvers such as braking, sudden lane changes, and minor changes in direction within a lane. In these short‐term maneuvers, high friction demand can exist but the discomfort threshold may not be perceived in time for the driver to take corrective action.”
2011 AASHTO Greenbook
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
Kentucky Results
High Friction Surfaces • 32 sites selected and installed in 2009, 2010 and 2011 • Preliminary evaluation of 26 projects shows a 69% reduction in crashes
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
What is a High Friction Surface Treatment? • High Friction Surface Treatments (HFST) are pavement surfacing systems with exceptional skid‐ resistant properties that are not typically acquired by conventional materials • Generally proprietary resin‐based products and processes • Guidelines from the British Board of Agrément (BBA)“…defined as having a minimum skid resistance value (SRV) of 65 measured using the portable Skid‐Resistance Tester as defined in TRL Report 176: Appendix E.”
HFST Aggregates – Generally calcined bauxite or slags with high PSV, but flint, granite, and other materials have also been used – Generally 3‐4 mm maximum size Bauxite
Flint
Granite
HFST Binder Materials • Binder system (proprietary blends) – Bitumen‐extended epoxy resins – Epoxy‐resin – Polyester‐resin – Polyurethane‐resin – Acrylic‐resin
HFST Installation • Manually – Manual mixing of epoxy material – Manual application of epoxy with squeegee – Hand broadcast and distribution of aggregate – Production rates: 200‐500+ SY/hr.
HFST Installation • Automated (machine‐aided) – Machine mixing and application of epoxy (limited hand/squeegee work) – Machine broadcast/application of aggregate – Production rates up to 2,300 SY/hr.
HFST Finished Product
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
Roadway Departure Risk Strategy Keep Vehicles on Roadway Reduce Likelihood of Crashes Minimize Severity
Roadway Departure Crashes 2010 Nationwide Fatal Crashes 30,196 Fatal Crashes 15,786 Roadway Departures Source: NHTSA FARS
Roadway Departure Crash (RwD) - A non-intersection crash in which a vehicle crosses an edge line, a centerline, or otherwise leaves the traveled way.
FHWA Roadway Departure Strategic Plan RwD Fatalities by Most Harmful Event (FARS 2007-2009) 4,156
Overturn Opposite Direction Trees, Shrubs
18,530 Signs, utility poles, traffic signals
3,694
Other Fixed Object Barriers
11,452 14,374
Embankments, Ditches, Boulder, Snowbank Other
Roadway Departure Fatalities Most Harmful Event (FARS 2007-2009) Nearly ¾ of Roadway Departure Fatalities are from 3 crash types.
31% Overturn Opposite Direction Trees, Shrubs
19% 24%
Roadway Departure Fatalities Most Harmful Event (FARS 2007-2009)
45% in HC Overturn Opposite Direction Trees, Shrubs
48% in HC 36% in HC
Fatal Horizontal Curve Crashes
72%
Horizontal Curves and Safety 6.7 7
Average crash rates for horizontal curves is about 3 times that of tangent segments
6
Crashes/km
5 4 3
2.21
2 1 0
Tangent Segments
Curves and Transitions
Source: Glennon, et al, 1985 study for FHWA
Strategies for Reducing Crashes (Where Can HFST Benefit Safety?) 1. Horizontal curves 2. Approach to intersections 3. Grades When the pavement has:
Marginal friction effected by weather Low friction Friction values not compatible with approach speeds and geometrics (friction demand)
Skid related crashes are determined by many roadway factors: Weather Conditions Friction Demand Road Geometry Vehicle Speeds Traffic Characteristics Driver Actions Source NCHRP 108
Conceptual Relationship Between Friction Demand, Speed and Friction Availability
Source NCHRP 108
AASHTO Horizontal Curve Design Model a
a
e = superelevation f = side friction factor V = design speed (mph) R = radius of curve (ft)
e+f = V2/15 R
Side Friction Demand, g Relationship between curve speed and side friction demand for two radii
Source TRR 2075
What about Friction Demand? In an existing curve the following is known: • superelevation, • radius • curve approach speed
Solve for friction demand: Fs = V2 ‐ e 15R
Basis for AASHTO Curve Design Model Is Driver Comfort Although the curve design policy stems from the laws of mechanics, the values used in design depend on practical limits and factors determined empirically over the range of variables involved.
Improving Friction to Keep Vehicles on the Roadway AASHTO Design assumes vehicles: do not exceed the design speed traverse the curve following a constant radius.
Likelihood of skidding increases when these assumptions are violated. Several studies have shown that under real world conditions both of these assumption are violated. Source NCHRP 500 Volume 7
Speeding- Related Crash Typology When crash types were examined for these drivers excessively speeding, researchers found that speeding was the leading cause of single‐driver right or left roadside departure with traction loss and the third leading cause of head‐on crashes. …primarily on curves, at night, on local or collector roadways, and during clear weather.
Truck Operations on Curves Skidding trucks may lead to overturn Friction demand varies per tire Trucks on downgrade curves generate greater lateral friction demand Margin of safety for ‘f’ is lower for trucks Trucks with high centers of gravity may overturn before losing control due to skidding Source NCHRP 505
“Where practical, the maximum side friction factors used in design should be conservative for dry pavements and should provide an ample margin of safety against skidding on pavements that are wet as well as ice or snow covered. The need to provide skid‐resistant pavement surfacing for these conditions cannot be overemphasized because superimposed on the frictional demands resulting from roadway geometry are those that result from driving maneuvers such as braking, sudden lane changes, and minor changes in direction within a lane. In these short‐term maneuvers, high friction demand can exist but the discomfort threshold may not be perceived in time for the driver to take corrective action.”
2011 AASHTO Greenbook
Overview • What are High Friction Surface Treatments? • RwD Crash Reduction Strategy using HFST? – Pavement Friction Demand and location selections for HFST • Why HFST?
Kentucky Results
High Friction Surfaces • 32 sites selected and installed in 2009, 2010 and 2011 • Preliminary evaluation of 26 projects shows a 69% reduction in crashes
