The correct amount of pavement friction is critical for motorist safety, especially during wet weather.
The Wet Surface Crash Reduction Program guidelines from the Texas Department of Transportation (TxDOT) Traffic Safety Division provide engineers with a framework for identifying existing pavement friction and the tools for specifying new pavement surfaces that will meet project-specific friction demand. During the past few years, there have been issues with some flexible pavements having lower-than-expected friction skid values. These concerns were for newly constructed pavements; normally, friction skid values decrease only several years after construction.
Researchers with the Texas A&M Transportation Institute (TTI) recently completed a synthesis study to evaluate Form 2088, the Surface Aggregate Selection Form, which is used to provide guidance on selecting proper roadway friction treatments.
“In TxDOT, we have a program called the Wet Surface Crash Reduction Program,” says Robert Trevino Flores, director of the TxDOT Soils and Aggregate Section. “This program provides the framework for identifying existing pavement friction. Form 2088 is one of those tools used in the program to determine the friction availability and demand. This project tried to evaluate those criteria and make sure that the form is really helping us make the best decisions for our pavements.”
This synthesis study searched available information pertinent to the criteria used for Form 2088 to find the surface aggregate classification and determine the criteria used by other states and governing agencies to determine the friction availability and demand.
“What we wanted to look at was the criteria on the form to see if there had been research since the form was created in the late 1990s,” says Darlene Goehl, head of the TTI Pavements and Materials Division. “Our goal was to update those criteria based on the latest research.”
The project found improvements in the program that triggered two research statements. The first statement was the evaluation of surface types, pavement friction and wet weather accidents. The other project was incorporation of the findings in a different type of form.
“We also recommended that they look at the safety spreadsheet that TTI developed and the districts are starting to use,” says Goehl. “A lot of the criteria that are on the form are also captured in that safety spreadsheet, so we think it’s an efficient use of resources to just have that one form. We also made recommendations on the aggregate being used to include some friction values.”
With the proper guidelines in place for the Wet Surface Crash Reduction Program, the traveling public will benefit from safer roadways.
“Safety is our priority here at TxDOT,” notes Flores. “It is critical to address the safety of the traveling public, and it is important that we are using the correct criteria on the form to make the pavement surface optimized for correct friction values.”