Pavement surface friction has always been an important issue because it influences roadway safety. It's especially important considering there are 1 million wet-weather traffic accidents, 40,000 work zone accidents, and some 42,000 fatalities occurring on U.S. highways every year, according to the Federal Highway Administration (FHWA).

These startling statistics raise serious questions about whether the nation's highways provide the necessary surface characteristics. For anyone who has ever skidded or slid on a roadway, the importance of a pavement's surface friction is undeniable.

Surface friction (or skid resistance) is the characteristic that allows tires to "grip" the pavement, thereby allowing vehicle steering and braking.

Surface friction depends upon a complex interaction involving the way a vehicle is driven; pavement surface characteristics; tire performance; and, of course, the presence of water, oil, etc., on the pavement.

Proper pavement surface characteristics during pavement construction or rehabilitation may mitigate or even prevent accidents and incidents related to hydroplaning, over-steering, and excessive skidding (which requires longer than average braking distances). Skid resistance is an increasingly important factor as agency/owners, contractors and others endeavor to make our highways safer.

Concrete pavements have some inherent and widely known friction characteristics, but skid resistance is not the only variable in quality pavement design and construction. Other issues, including sound at the tire/pavement interface; splash and spray; reflectivity; and heat absorption/reflectance, also must be considered.

Working together, the American Concrete Pavement Association (ACPA) National staff and a number of Chapter/State executives and promoters are evaluating how friction is measured, as well as what the reasonable "skid" values are from state to state.

ACPA is compiling a database of friction numbers and other variables from state agencies. The goal is to develop a range of reasonable surface friction (skid resistance) values, which factor in a host of variables, including mix designs, aggregate types and other contributing surface characteristics.

ACPA also is conducting and supporting research initiatives on innovative texturing to satisfy requirements for friction, sound and durability.

The Association is evaluating a range of surface types, including two-lift construction, porous pavements and exposed aggregates. One early finding in this evaluation is that concrete is inherently more durable than rubberized asphalt pavements, which lose both their sound qualities and their friction resistance over time. This translates into more frequent repair and rehabilitation cycles, which, in turn, increases traffic congestion and the perils of work-zone accidents.

In addition, ACPA is directly involved with the National Cooperative Highway Research Program and its project 1-43, which is developing a guide to pavement friction. ACPA is also maintaining active dialogue with key stakeholders — including state and federal agencies — to gain insights and ideas, while also sharing information and promoting best practices.