Drivers may think the only thing standing between them and a collision in rush hour traffic is their brakes, but really the friction generated as their tires move over a road’s surface has a lot to do with stopping ability.
It is what the Texas Department of Transportation calls skid resistance. In short, if the surface texture of a road is too smooth it can not only negatively affect stopping time, but also increase the chances of hydroplaning on rainy days.
For the last 10 years, one University of Houston Cullen College of Engineering researcher has been working with TxDOT to improve driver safety by revolutionizing the way this wear is tested on some 80,000 centerline miles of highway across Texas.
“Before this laser system we developed, TxDOT could only do what is called a sand patch where they use a bucket of sand and then they use a spreader to spread it in a circular fashion,” said Richard Liu, professor of electrical and computer engineering. “It was time consuming and it did not offer an accurate picture of road surface damage.”
This has all changed. Several of Liu’s vehicle-mounted laser devices are now being used to deliver thousands of miles of data on road texture conditions to TxDOT crews as they travel at speeds of up to 60 mph.
Each year, the agency has provided Liu funding to further improve on the design of four generations of his system. This month, TxDOT renewed their interagency contract with Liu, providing up to $300,000 in support over the course of the next two years to maintain their current systems and develop a fifth-generation model with improved power, water tightness and measurement accuracy.
Created to mount on the front of one of a few specialized vans in the TxDOT fleet, the device sits about 12 inches above the road’s surface. One box, equipped with a laser, is mounted above the right wheel pass and takes eight different readings for each millimeter of distance traveled.
“It is just like a ruler, but it is a very accurate and very fast ruler,” Liu said. “The system shoots the laser that measures the distance from the vehicle to the road surface. If there is a dip, the laser travels a little farther. The accuracy of the measurement can be within a few micrometers, so it’s very accurate.”
It’s on-board microprocessor then sends the data to the main computer in the van, allowing TxDOT crews to see recorded assessments of the road surface on their screen.
Should crews find an area that doesn't meet their required skid resistance rating, the device is capable of pinpointing the location of the problem within a few inches thanks to a global positioning system and a distance measurement instrument inside the system.
This most recent contract will allow Liu to add a few upgraded fifth-generation models to TxDOT's fleet as well as further improve his laser system's performance on those already in use by the agency. The capabilities of these newer models, however, will far exceed what is on the road to date.
One of the main differences is increased accuracy and stability of the laser.
“Skid is tested annually on the Texas roads,” said John Wirth, a pavement-engineering specialist with TxDOT who oversees Liu’s contract. “Right now, it takes four years to get an overall assessment of the entire state. Adding more units, with improved accuracy, could allow us to get 100 percent in one year.”