continuous friction measurement and high friction surface
TRANSCRIPT
Continuous Friction Measurement and High
Friction Surface Treatments
Andrew Mergenmeier, P.E.
Senior Pavement and Materials Engineer
USDOT-Federal Highway Administration
July 26, 2018
Agenda
Continuous Friction Measurement
• Are there road sections where friction is impacting crash risk?
• What is US standard network level friction measurement?
• What is continuous friction measurement?
• Field Data
High Friction Surface Treatment
Pavement Conditions Vary
NCHRP Report 37, 1967:
• “Because the intensity of the polishing process
increases markedly with tread element slip, all other
factors being equal, the lowest friction levels are found
on high-speed roads, curves, and approaches to
intersections; in short, in locations at which high friction
values are needed most.”
Concept of in service pavement conditions varying every foot (thus the
need for continuous friction measurement) is in line with current efforts
to assessing pavement density continuously vs sampling (Intelligent
Compaction, Infrared Technology, GPR) and structural capacity (TSD)
3
Annual ALL RAMPS CURVES
Wet Avg. 90% 90% 84%
Dry Avg. 77% 78% 80%
Total Avg. 87% 89% 82%
(As of 6/22/2015)Crash Reduction % (60 locations)
Nationwide, very few HFST installations were from sites
identified by network level friction testing.
Kentucky HFST Program - Crash Reductions
US Standard Friction Test Method for
Highways is a Locked Wheel Skid Tester
which is a Sampled Based Friction Testing
(not continuous)
Locked-Wheel Skid Trailer – 40 mph 60’ test sample
Source: Virginia Tech Transportation Institute
County Road Friction Test
Source: ICC youtube
Continuous Friction Measurement
Rubber Tire test continuously measuring every foot of pavement (study –
microtexture)
Laser based texture measurement system measuring every foot of
pavement (macrotexture)
Microtexture Macrotexture
What is texture
Aggregate
Pavement Cross
Section
FHWA Pavement Friction Management
Study
• Study initiated based on:
• Support goal to zero fatalities
• FHWA friction measurement demonstration experience
• International road and domestic airfield experience
• Assist 4 States in developing and demonstrating Pavement
Friction Management Programs (using continuous
pavement friction and texture* measurements, crashes,
and other data)- Obtain friction, texture, crash, traffic, other data.
- Define friction demand categories.
- Set investigatory levels of friction/texture.
* Texture = macrotexture
Standard Safety Analysis Methods
Safety Performance Functions, relate crashes to several
factors FHWA General (SPF)
• X1, X2, …, X n
- Explanatory variables
P: Number of crashes on segment L
AADT: Traffic count
Xi: Friction, Texture, Curvature, cross-slope, grade, etc.
Friction Demand Categories - Investigatory Friction
Thresholds
In support of NCHRP 37 statement on low available friction at
high friction demand locations (curves/intersections)
• Friction below a given threshold should result in
an investigation to determine if a treatment is
needed
• Friction threshold should not be the same for all
road segments
Low friction data is not a reason to automatically invest in a
treatment – it is one piece of information
0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65
A Motorway
B Dual carriageway non-event
C Single carriageway non-event
QApproaches to and across minor and major
junctions, approaches to roundabouts
KApproaches to pedestrian crossings and other
high risk situations
R Roundabout
G1 Gradient 5-10% longer than 50m
G2 Gradient >10% longer than 50m
S1 Bend radius < 500m - dual carriageway
S2 Bend radius < 500m - single carriageway
Investigatory level (50 or 80 km/h)
Site category and definition
Friction Demand - Investigatory Levels
(UK-English)
Case Studies
1. Importance of Continuous Measurements – rural
2. Importance of Continuous Measurement - urban
3. High Friction Surface Treatment
CASE 1 - Importance of Continuous Measurements
Comparison CFME and texture data collection with 1 LWST test per
1.0 mile
SR A MM 54-
60
State Route A (MM 59.8)
“Because the intensity of the polishing process increases markedly with tread element slip, all other factors being equal, the lowest friction levels are found on high-speed roads, curves, and approaches to intersections; in short, in locations at which high friction values are needed most.” NCHRP Report 37, 1967
1. Good SR 50-552. Fair SR 45-503. Poor SR 40-454. Very Poor SR 35-40
1 2
3
4
5
1. MM 56.0 2. MM 57.1 – 57.23. MM 59.04. MM 59.75. MM 59.8
SR A MM 56-
60
Case 2 - Importance of Continuous
Measurement - urbanSignalized Intersection
Advancing Transportation Through Innovation
Advancing Transportation Through Innovation
MM 6.64
SR30 44.0
MPD 0.73
MM 6.79
SR30 40.0
MPD 0.28
MM 7.02
SR30 40.0
MPD 0.29
Case 3 - High Friction Surface Treatment
Interstate Ramp HFST
Friction (SCRIM and LWST) and MPD Texture
Average SR30 89.0
Average FN40R 80.2
Average MPD 1.25 mm
Source: VaTech
Assist in
defining
HFST
installation
termini
What is a High Friction Surface
Treatment?
High Friction Surface Treatments (HFST) are pavement surfacing overlay systems with:
- exceptional skid-resistant properties that are not typically acquired by conventional materials
- and retains the higher friction property for a much longer time.
Commercially available resin-based products and processes
Generally applied in short sections to improve spot locations
where friction demand is critical
Safety webpage
https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/
High Friction Usage
Aggressive use
At least one site
No sites
Multiple sites (5+) = National Demo Project
under SEAHC
HFST National Status ( as of 3/5/2013)
State DOT HFST Status Active implementation as of 12/1/2017
10 – 50 curves
One curve
No curves
2 – 10 curves
NJ, DE,
MA
50 – 100 curves
Over 100 curves
MD
Over 2 million S.Y.
FHWA effort in promoting HFST as a safety
countermeasure
On-going research projects –
• CMF - Additional analysis to develop crash modification factors for HFST is underway as part of FHWA’s Evaluation of Low-Cost Safety Improvements Pooled-Fund Study.
• Development of Thin Lay asphalt based high friction surface treatment
• Surface Evaluation and Performance monitoring for HFST using 3-D Laser Technology
Enhancement to the Office of Safety –Roadway Departure/Pavement Friction web page:
• High Friction Surface Treatment Curve Selection and Installation Guide
• Case studies and Noteworthy Practices from Penn DOT, Iowa DOT, South Carolina DOT, Caltrans, Kentucky Transportation Cabinet, Tennessee DOT, Texas DOT and local counties and cities.
• HFST FAQ updated in 2017
• NCAT HFST Alternative Aggregate Study.
FHWA effort in promoting HFST as a safety
countermeasure
Partnering with ATSSA High Friction Surfacing Council (HFS)
• HFST technology and installation video
• HFST Installation and Inspection Training course
• On-going effort to create a forum between ATSSA HFS and state DOTs for technology exchange and provide opportunities for Q and A with manufactures, suppliers and contractors.
Additional outreach and technical assistance
• Conduct in-person peer exchanges with multiple state DOTs with emphasis on HFST and installation demonstration.
• Deliver RwD Safety Plan to Roadway Departure Focus States state withHFST treatment in the countermeasures recommended on curves
Conclusion
Measuring friction continuously (macro and micro), especially when
complemented by road geometry, traffic, and crash data, provides
a more effective method for identifying the most critical sections
and allow focusing the safety improvement efforts on the higher
risk locations, such as intersections and curves.
Hopefully the potential value of continuous friction measurement to
assist you in effectively and efficiently reducing crashes has been
demonstrated, so you will pursue assessing continuous friction
measurement beyond this presentation.
Thank You
Andrew Mergenmeier P.E.
Senior Pavement and Materials Engineer
U.S. Department of Transportation
Federal Highway Administration
FHWA Resource Center