The WesTrack pavement loading objective is 10 million Equivalent Single Axle Loads (ESAL) or 1.7 million total vehicle miles over a 2-year period. The test is designed to accelerate 10 years or more of pavement loading. To accomplish the pavement loading, four triple-trailer vehicle combinations are being operated an average of 15 hours per day over the 2-year period at the test speed of 64 kph (40 mph). To facilitate the aggressive pavement loading requirement, WesTrack utilizes driverless vehicle technology to allow near-continuous vehicle operation in an otherwise monotonous driving environment. Within a one-year period, the Nevada Automotive Test Center designed, fabricated and certified the system for the autonomous operation of four triple-trailer vehicle combinations weighing 670 kN (152,000 lb. each).
A team of truck and truck component manufacturers was assembled to support the test and provide the best in advanced transportation technologies. The vehicle team members participating in the WesTrack project include the following companies:
The driverless vehicle system utilizes a guide-by-wire system for the lateral and longitudinal control of the trucks. Additionally, every system controlling the trucks was designed with a backup in the event of primary system failure. All track and control room systems are connected to uninterruptable power supplies in the event of power loss.
The trucks are guided by primary and backup wires buried under the asphalt, giving a continuous feedback signal to the steering controller. Audio amplifiers power the two continuous wire loops installed around the track. Each vehicle is equipped with guidance antennas mounted to the front bumper to acquire the guide tones emitted by the redundant wires. The vehicle antennas are capable of reading either primary or alternate wire paths. A Proportional Integral Differential (PID) control loop is used within the control system to guide the trucks. A robust stepper motor is connected to the steering gear box and controls steering based on feedback from the antenna and the error signal generated from displacements from the center of the wire.
The four trucks are controlled and monitored through a control room located beside the test track. Computers within the control room are used to initiate the starting and stopping of the vehicles and to regulate vehicle spacing and speed for traffic control purposes.
The traffic control and longitudinal control utilize Radio Frequency (RF) serial modems to communicate with the four trucks. Each truck has an RF serial modem for sending/receiving information packets to the control room. The control room has four RF serial modems for sending and receiving information packets from each truck. Each modem is on a separate frequency. As a final judge of the vehicle spacing, a Differential Global Positioning System (DGPS) independently monitors the position of the trucks and provides a fail-safe input to the traffic control computer.
Each vehicle has two computers, one for vehicle control and one for vehicle monitoring. The computers are located in the sleeper of the truck in a shock mounted cabinet. The guidance and steering control activates the steering actuator connected to the steering system. The monitoring computer checks truck health that includes more than 160 parameters normally evaluated by a driver.
The control room operator has one computer for each truck that displays the status of the truck in an easy-to-read format and has diagnostics to aid in monitoring and correcting critical control parameters. A vehicle monitoring computer checks the critical components and provides decisions to the control computer on the status of the vehicles. If a critical parameter is out of bounds, the vehicle monitoring computer will transmit a shut-down signal to the control computer.
NATC has automated the control of the throttle, engine and transmission by using advanced electronics on the engine and automatic transmission electronic control unit. The brake interface builds upon Midland-Grau's electronic brake valve and controlling circuitry. Midland-Grau's Anti-Lock Brake Systems (ABS) have been installed on the truck and all trailers to allow controlled stopping during normal and emergency braking.
WesTrack implements a unique pavement measurement capability not available at any other pavement research facility. Through the driverless vehicle controls, the lateral and longitudinal location of the truck is precisely defined at all locations around the track. This allows the longitudinal location of the trucks to be defined within 50 mm (2 in.) of any measurement sensor installed in the pavement. This exact alignment includes all the phase delays associated with the data acquisition computers on the truck and data acquisition computers for the track.
There are 26 experimental pavement test sections located in the track. In each of the 26 sections, a grid of five longitudinal and five transverse pavement strain gages has been installed. These are located at the center of the left wheel path spaced 300 mm (1 ft.) apart. A computer is used to record the pavement strain gage signals at a rate of 1,022 samples per second.
One of the triple-trailer vehicle combinations is instrumented at each axle end with accelerometers and shear strain gages. This instrumentation allows investigation of vehicle dynamics with respect to stationing along the track and measurement of dynamic loadings as each truck axle passes over the pavement strain gages. The alignment and correlation of pavement strains with dynamic forces on the vehicle will allow a unique investigation and model validation tool for the on-going WesTrack research.
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 (703) 285-2434, Fax (703) 285-2767
