Paving the Way for Safer, Smoother Asphalt Roads

By Nick Davis, Contributing Author

Asphalt pavements are essential to our transportation network, but are plagued with constant challenges due to traffic and weather conditons. Issues like surface roughness, reduced friction, hydroplaning risks and general wear can compromise driver safety and increase maintenance costs. With aging infrastructure and increasing traffic demands, the need for cost-effective, long-lasting solutions has never been greater.

That’s where diamond grinding and grooving come into play. 

Diamond grinding and safety grooving are two distinct but complementary surface treatments that restore pavements to optimal condition. While these techniques have been used on concrete for decades, their application on asphalt is more recent and delivering impressive results —enhancing roadway safety, longevity and performance.

The Science Behind Grinding and Grooving

Diamond grinding is the process of gently abrading the top surface of pavement using a machine equipped with closely spaced diamond saw blades. The removal of this thin layer of pavement eliminates irregularities such as ruts, bumps and cracks resulting in a smoother, quieter ride with improved friction. Unlike overlays, grinding can be performed in more diverse temperatures, effectively extending the construction season. 

When employing a longitudinal surface texture, the diamond grnding process results in a reduced road noise far quieter than transverse scoring or milled (standard or micromilled) asphalt. 

An additional benefit of the gentle abrasion process — often more than 27 million diamond contacts per square yard — is the delivery of a remarkably flat surface at the macro level, optimizing both rideability and friction.

Safety grooving involves cutting narrow, discrete channels into the pavement surface to improve drainage. These grooves direct water away from the tire-pavement interface, significantly reducing the risk of hydroplaning and improving vehicle control in wet conditions. 

Grooves can be applied transversely or longitudinally to substantially reduce wet-pavement accident rates. However, longitudinal grooves (which run parallel to the direction of traffic) are particularly effective at resisting lateral vehicle motion, keeping drivers safely in their lanes without additional highway noise.

Landmark studies, such as the 1972 California Department of Transportation’s (Caltrans) report “The Effect of Grooving on Motor Vehicle Accidents,” found that grooved pavements saw a 70% drop in wet-pavement accidents, a 50% decline in fatal incidents and a 20% reduction in total accidents. The study also reported a 99% drop in vehicle highway departures. Later tests conducted by the National Center for Asphalt Technology (NCAT), several state transportation agencies and universities validated these findings and the texture’s durability. 

Grinding and grooving techniques are typically more cost-effective and less disruptive than traditional asphalt overlay projects that are resource-intensive, produce significant construction waste and often cause costly traffic disruptions. 

Meanwhile, grooving and grinding allow agencies to target specific surface issues (i.e., ride quality, friction, noise) without the extensive materials and time associated with a full repaving project, making them efficient pavement preservation tools.

Real-World Applications

State departments of transportation (DOTs) are increasingly turning to diamond grinding and grooving to address specific challenges on their asphalt roadways, as displayed in the following case studies: 

Enhancing safety in Ohio — The Ohio Department of Transportation (ODOT) has utilized longitudinal diamond grooving on asphalt pavements since 2012, inspired by its success on concrete bridge decks. Skid tests were conducted on Interstate 75 in Montgomery County due to a high crash rate among commercial trucks navigating the highway’s curves. The test results showed a need for an improved macrotexture. After a two-mile stretch was ground and grooved, the average skid number (SN 40) improved by more than 70%, and crash data showed a dramatic reduction in accidents. Issues on the northbound lanes were virtually eliminated. 

Similar results were observed on Ohio State Route 126 in Hamilton County, where longitudinal grooving reduced skid-related crashes and nearly halved vehicle highway departures during wet conditions. In Cuyahoga County, lanes on Interstate 90’s Innerbelt Curve were treated with grooving after Superpave mix issues reduced macrotexture — improving the average skid number by more than 50%.

Single-lift smoothness in South Carolina — On South Carolina Highway 544, a high traffic, four-lane corridor, time was of the essence during the repaving of three separate sections in 2020. Instead of following the traditional approach of placing multiple asphalt lifts and applying a final friction overlay, the South Carolina Department of Transportation (SCDOT) placed a single, thick lift and performed diamond grinding to speed up construction. This approach saved money, conserved resources and minimized traffic disruption and resulted in an ultra-smooth, high-friction surface quieter than the original pavement surface. Independent rideability tests conducted before and after diamond grinding showed an average 56% reduction in roughness.

Diamond grinding was particularly helpful in seamlessly connecting new pavement sections to bridges, eliminating rough transitions that compromise ride quality. 
Not only did diamond grinding save SCDOT time and money, it also set a precedent for similar high-traffic corridors across the state. 

Extending service life in Missouri — When U.S. Route 412 began to show signs of cracking and rutting, the Missouri Department of Transportation (MoDOT) chose diamond grinding over applying a thin overlay. MoDOT’s previous experiences using diamond grinding validated the process’ ability to address texture loss and meet tight smoothness specifications. For this project, grinding down the corridor’s middle hump effectively removed ruts and reshaped the wheel paths, improving both ride quality and surface drainage. International Roughness Index (IRI) measurements decreased by 40 inches per mile, and the anticipated lifespan extension—five to seven years — rivals that of thin overlays with lower costs and considerably less materials.

Maximizing ride quality in New York — New York State allows up to 5% of a pavement project’s total surface area to be diamond ground for ride quality. During a resurfacing project on Interstate 787 in Watervliet, the contractor strategically allocated the entire 5% allowance to diamond grind two ramps that had previously underperformed in terms of smoothness. This resulted in a 40% reduction in IRI, making the ramps the smoothest and quietest sections of the entire project and earning the contractor a pay incentive. Following this project’s success, the New York State Department of Transportation (NYSDOT) increased allowable grinding limits to 20% of asphalt paving projects and now demands an entire pavement section to undergo a production grind if more than 20% of the surface area is in need of grinding. 

In southeastern states, agencies are reconsidering open-graded friction courses, which are prone to raveling, in favor of dense-graded asphalt treated with safety grooving. Globally, countries like South Korea, Australia, Thailand, Chile, Germany and many others have applied diamond grinding on major highways to restore smoothness, extend service life and support sustainability. By reducing fuel consumption and tailpipe emissions and promoting road safety, diamond grinding and grooving have begun to play a key role in the modernization of vital infrastructure.

Technical Insights and Performance Benefits

Modern diamond grinding and grooving equipment is a far cry from early iterations. New equipment offers more horsepower, wider grinding heads and more durable wheelbases, making production faster with a more desirable final ride. Digital tools like the International Grooving & Grinding Association’s Fuel/Carbon Savings Calculator quantify the environmental benefits of diamond ground surfaces — translating roughness reductions into measurable fuel and CO₂ savings for highway users.

The benefits of grooving and grinding include:

• Improved safety: Increased skid resistance and improved water drainage reduce wet-weather accidents, including hydroplaning. In California, grooved pavements saw a 70% drop in wet-weather accidents over five years.
• Longer service life: Surface restoration extends the lifespan of pavements and preserves their underlying structure by reducing dynamic loads.
• Cost and resource savings: Grinding and grooving methods can be performed at a fraction of the cost of a full overlay, allowing agencies to maximize their maintenance budgets. The process also generates less construction waste and allows for the continuous use of roadways with minimal closures. 
• Enhanced ride quality: Smoother surfaces reduce vehicular wear and tear, lessen road noise and provide a more comfortable driving experience.
• Improved sustainability: Smooth pavements reduce dynamic loading on vehicles, cut fuel use and lower emissions. Environmental calculators provide clear data for agencies aiming to justify green infrastructure investments.
• Reduced roughness: Reductions in roughness mean less wear-and-tear on vehicles, a quieter ride appreciated by both drivers and nearby communities and a more attractive driving experience overall.
• Versatility and flexibility: Both processes can be adapted for new or existing pavements and serve to correct isolated rough spots or treat full corridors as needed.

Key Considerations for Implementation

Agencies considering grooving and grinding treatments must consider certain factors, such as initial costs and the logistics of project execution. Despite specialized equipment and operator training requirements, the long-term benefits routinely justify the upfront investment.Grinding does not hinder future overlays, therefore maintaining flexibility in long-term asset management.

The best candidates for these treatments are pavements that are structurally sound but exhibit surface-level wear, texture loss or friction deficiencies.  

The Future of Asphalt Pavement Maintenance

The growing adoption of diamond grinding and grooving is not accidental. As states and countries worldwide seek resilient and sustainable infrastructure, these proven strategies have moved into the mainstream. Advances in machine technology — such as better production rates — drive further gains in efficiency and consistency. Agencies are now leveraging real-world data to fine-tune specifications and justify funding to pursue climate-conscious pavement preservation methods.

In developing nations with heavy traffic conditions, pilot projects, public-private partnerships and training programs are laying the groundwork for wide-scale implementation. These methods support economic growth by delivering safer, longer-lasting roads that reduce life-cycle costs.

For road owners, engineers and policymakers, it’s time to embrace these proven surface treatments on a larger scale. By doing so, we can pave the way for safer, smoother and longer-lasting roads for everyone.

Nick Davis is the director of technical services at the International Grooving and Grinding Association and heads the American Concrete Pavement Association’s Emerging Leaders Group.