California Department of Transportation

Mobile Router Robots

A tethered mobile robot is a self-propelled, automated device that can operate intelligently in close proximity to a support vehicle. The use of mobile robots can enhance worker safety, reduce maintenance costs, and improve operational efficiency.

Mobile Router Robots
Mobile Router Robots

The Tethered Mobile Router Robot (TMRR) developed by AHMCT is a wheeled mobile robot developed to rout pavement cracks prior to sealing. The centrally located routing device is a hydraulically driven impact star cutter wheel mounted in a compact wheeled frame. The differentially steered wheeled robotic cart is driven by electrical servo motors directly coupled to each of its two drive wheels. The robot frame has a rotating collar on top to provide rotational data, a connection for positional encoder reference and a connection passageway to the router. The body of the robot frame provides for a three point contact with the router device within.Air cushions provide the actual contact, transferring the robot pushing forces to the router and isolating the vibrations the router creates from the robot.

The TMRR is not a fully automated system, but instead relies on operator supervision input and control. The operator manually joystick controls the TMRR over to a crack and when recognized, the automated crack following controller can follow and rout the crack automatically.

Automated crack following is accomplished with the use of a scanning laser range sensor that is installed on the front of the robot. The sensor is slide-mounted to provide the necessary field of view as the robot is guiding the router along a crack.

A support vehicle provides all power and materials through the use of a tether, and also contains a vision based computer sensing system for crack identification. The robot position relative to the support vehicle is thus necessary, and it is accurately measured through a cable extension transducer based system.

Robots envisioned for use in highway maintenance differ from conventional robots in many ways. Commercially available, conventional robots usually perform repetitive manufacturing tasks, moving objects from place to place. Highway maintenance operations are generally more complex, because they must follow paths not conforming to pre-set patterns.

Conventional robots also have a comparatively low load capacity relative to their weight. Highway maintenance tools, such as pavement routers and paint nozzles, are heavy and exert extreme forces during operation. Thus, highway robots must be built strong enough to withstand the rigors of highway tasks while still operating with high precision. Many highway maintenance operations currently use materials and tools attached to, or supplied from a support vehicle. Numerous operations require power tools that are dependent upon remotely-located energy sources, such as vehicle-mounted generators, compressors, or engines. Accordingly, a physical attachment is necessary between mobile robots for highway maintenance and the support vehicle.


The TMRR is the same routing device developed and demonstrated on the longitudinal portion of the SHRP-107A, ACSM project.

The TMRR was first developed in a laboratory to verify positional control and laser guided crack following abilities. With programming and control issues resolved, the TMRR was installed on the ACSM platform for road testing. A modified liftgate was developed to quickly deploy and retrieve the TMRR from the rear of the ACSM truck. Deployment and operation is done remotely so workers are not required to be exposed directly to traffic hazards.


The TMRR routing abilities were demonstrated in the Spring of 1999 on asphalt roads at our facility. The TMRR was able to route a 3/4" by 3/4" profile in asphalt roadway at speeds above two miles per hour, and it was able to follow any path regardless of its shape.

Upon successful demonstration of the TMRR routing abilities in the Spring of 1999, further development of this system has been halted. The agency sponsoring this aspect of development is in a climate zone that does not generally necessitate crack routing prior to sealing. Caltrans was generous to support our center in the achievement of the last remaining SHRP goal, to demonstrate random crack routing ability, but requesting further funding was not deemed reasonable. Interest must come from states where the climate zones dictate routing cracks, for this center to resume the development of this automated machine.