WesTrack refers to an experimental road test facility constructed in Nevada under a contract awarded by the Federal Highway Administration (FHWA). The project, entitled "Accelerated Field Test of Performance-Related Specifications for Hot-Mix Asphalt Construction" (Contract No. DTFH61-94-C-00004), has two primary objectives:
Accomplishment of these objectives is being achieved primarily by the construction, loading, monitoring, and performance evaluation of 26 experimental hot-mix asphalt pavement sections along a 2.9 km (1.8 mi.), oval test track. The track is located on the Nevada Automotive Test Center proving grounds about 100 km (60 mi.) southeast of Reno. Because the climate at the site is dry (typically less than 100 mm (4 in.) of precipitation per year) and experiences no frost penetration, it is well suited for evaluating the direct effects of deviations of materials and construction properties.
One of the subtasks on the project involves the use of autonomous (driverless) vehicle technology to achieve the desired 10 million, 80 kN (18-kip) equivalent single axle load applications. Four triple trailer combinations are operating on the track up to 22 hours per day, 7 days per week during the 2-year loading period.
U.S. Department of
Transportation Federal Highway Administration
Besides FHWA's role as project sponsor, the WesTrack Team consists of seven organizations, each with a specific role in the project:
Nevada Automotive Test Center (prime contractor, track loading, vehicle operation, driverless vehicle integration)
Nichols Consulting Engineers, Chtd. (experiment design, performance monitoring, PRS development)
Granite Construction Co. (track construction)
Harding Lawson Associates (track geometric design, construction inspection, quality control/quality assurance testing)
University of Nevada, Reno (pavement research, conventional hot-mix asphalt testing)
Oregon State University (SHRP hot-mix asphalt testing, data analysis)
University of California at Berkeley (SHRP hot-mix asphalt accelerated performance testing)
Huntway Partners, Inc.: Custom-Blended Asphalt
ROADTEC: Asphalt Materials TransferVehicle
Principal Investigators for the WesTrack Team are Dr. Jon Epps (University of Nevada, Reno) and Dr. Sirous Alavi (Nichols Consulting Engineers). The Program Manager is Henry C. Hodges Jr. (Nevada Automotive Test Center). The Project Manager for NCHRP 9-20 is Dr. Ed Harrigan. Technical oversight on the project is provided by Drs. Terry Mitchell and Chris Williams of FHWA's Turner-Fairbank Highway Research Center in McLean, Virginia.
The track consists of two tangent sections connected by two spiral curves. All test sections are constructed on the straight tangents between the turnarounds. The tangent sections are 10.4 meters wide consisting of two 3.7 meter lanes and a 1.2 meter hot-mix asphalt shoulder outside of the test lane. There is a 1.2 meter gravel shoulder on the outside of the track and a 0.6 meter gravel shoulder on the inside of the track. The outside lane serves as the "test" lane while the inside lane serves as both a shoulder and "trial" hot-mix asphalt placement lane. Each of the experimental sections is 70 meters in length; 25 meters for transition, 40 meters for performance monitoring, and 5 meters for destructive sampling.
Seven experimental factors related to the hot-mix asphalt surface layer were considered in developing the experiment design. These factors and their target levels are shown below:
These factors and associated levels were selected to obtain the most information relative to the effects of materials and construction variability on pavement performance.
The combination of these three factors and their levels is depicted in the factorial experiment design below. Note that six cells out of the matrix were eliminated (because of construction impracticality), leaving 21 potential mixes. To this, 5 replicants were added, resulting in 26 total sections. The numbers within each cell represent the randomized paving sequence of each section. In June 1997 an additional eight sections were built to replicate the coarse aggregate experiment with a different aggregate source.
* Numbers shown in each cell represent actual test section numbers.
The pavement loading is being accomplished using four triple trailer vehicle combinations. Navistar is supporting the test with four similar conventional tandem axle Class 8 tractors. A lead single-axle semi-trailer is followed by two single-axle trailers, providing a total of 10.3 ESALs per truck pass. To aid in the electronic control of the trucks through the driverless vehicle system, the trucks are equipped with a Detroit Diesel Series 60, turbo-charged, electronically controlled engine. Twin Disc automatic transmissions in each truck allows electronic control of the transmission. The trucks and trailers are equipped with a Midland-Grau Anti-Lock Brake System (ABS) and electronic brake valve for electronic control of the brake system. The trucks are equipped with 295/75R22.5 Goodyear tires. Each axle of the vehicle train is loaded to 89 kN (20,000 lb.), except for the front axle which is 53 kN, (12,000 lb). The test speed around the track is 64 kph (40 mph).
In addition to providing a basis for verifying and/or calibrating the current SHRP SUPERPAVE(TM) mix design procedures, this project will produce an advanced prototype performance-related specification (PRS) system for asphalt pavement construction.
A performance-related specification system for pavements is a method or model that permits pavement engineers to prepare practical specifications for pavement construction that focus heavily on the actual materials and construction practices that have the most effect on the long-term performance of the pavement. By considering the multitude of costs associated with the design, construction and future performance of a pavement, the system not only provides a means for identifying/specifying a cost-effective "target" pavement to build initially, but also provides a means for equitably rewarding or penalizing the contractor when the "as constructed" pavement is compared to that target. Under such a system, the contractor on a given job could be penalized for being slightly above the target specification for air void content and be rewarded for exceeding the target specification for initial smoothness. Assuming that the predicted long-term performance of the pavement is dependent more upon its initial smoothness than the air void content being slightly off-target, it is likely that (for this simple example) the net effect would be reward for the contractor and assurance for the client (road agency) that its funds were well-spent.
Under the current plan for PRS development, two types of systems will be developed. The first will be a sophisticated computer program that will have the ability to treat all design, materials and construction factors to a high level of detail. The second will likely be a relatively simple equation or matrix that will be somewhat less precise, but considerably easier to use. The later will focus only on those factors that have the quickest impact on pavement performance.
Construction of the test track was completed in October, 1995. Vehicle loading and performance monitoring began in April, 1996 and will carry on through June of 1998. Data analysis, research, and product development will require about one more year after the end of track loading. Project completion is targeted for March of 1999.
All inquiries regarding the WesTrack project and for the scheduling of any test track tours should be directed to:
info@natc-ht.com
Henry C. Hodges, Jr., Program Manager
WesTrack Public Information, Nevada Automotive Test Center
Post Office Box 234, Carson City, Nevada 89702
Telephone (775) 629-2000, Fax (775) 629-2029
or
terry.mitchell@fhwa.dot.gov
Terry Mitchell
Turner-Fairbank Highway Research Center
Telephone (202) 493-3147, Fax (202) 493-3161
Copyright - 1999 - Nevada Automotive Test Center - All Rights Reserved