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As the main contractors for the grooving of runways throughout the world, Roadgrip has been watching the current discussion over trapezoidal grooving versus the traditional grooving of airfields with great interest.


What is Runway Grooving?


Runway grooving significantly improves macro texture and drainage on airfield runways and reduces the risk of hydroplaning, making it easier and safer for pilots to control and brake the aircraft in wet weather. Take a look at the images below to see how effective grooving is.


Grooving works by cutting grooves into the asphalt or concrete with diamond blades to create channels in the surface for the rain to escape into, thereby stopping the water settling on the surface, which can cause skidding. The grooves on the runway act rather like the grooved tread of a vehicle tyre. These grooves are cut transverse to the direction of travel. This, in turn, improves the wet surface friction of the runway.



What is Trapezoidal Grooving?


Trapezoidal grooving (or diamond grooving) is a different shaped groove to the traditional groove.  It is the same depth (1/4 inch) but wider at the top with wider spacing between each groove (2.25 inches apart compared to 1.5 inches apart).  Source: FAA


The process, which is being championed and promoted heavily by a large American grooving company, uses a different blade cross section which creates a trapezoidal (or diamond) shape rather than the current square shaped groove.



Which Method of Grooving is Best?


The jury’s out on whether trapezoidal grooving is any better for safety over time – at this point.  We simply don’t have enough data over a long enough period to know yet.


However, a study has begun with various trials taking place in the USA.


The current data supports the hypothesis that trapezoidal grooving provides better water dissipation when the surface is newly cut, which makes sense as they are cutting away a greater cross section of asphalt. It’s a simple matter of physics that a groove or channel  8mm wide at the top, and 4mm at the bottom and 4mm deep has a greater cross sectional area than one that is 4mm x 4mm square.


Results also suggest the diamond shaped grooves potentially reduce the amount of rubber build up within the groove, which we agree is encouraging.  However, whilst the trapezoidal groove may show reduced rubber build up in the early life of the groove (due to there not being a right-angled edge to pick up the rubber), this could change over time.


The important point to consider is that all of these trials have been carried out on newinstallations. We all know there will be some wear that takes place to the groove corners during life and it’s this that we’re keen to learn more about.


In the case of traditional grooving, as the surface ages and oxidizes slowly, the grooves widen at the top edge to become slightly more trapezoidal in shape anyway. This, together with the improvement in micro-texture of asphalt as it ages, will show a general improvement in friction as grooves move toward mid-life.


We’re very interested to see a longerstudy so that comparable results can be measured over the life of the asphalt.  This will give us a true comparison between the two methods of grooving.


Who Offers Trapezoidal Grooving?


As far as our customers are concerned at Roadgrip, we’re happy to provide either method of grooving, although, due to the patent filed by the American organisation, it has unfortunately pushed costs up for trapezoidal grooving at this time.  Whether there is any benefit long term in paying that higher cost for trapezoidal is unknown.


We’ll keep you updated on new findings as we learn them, and we’re very happy to talk through the debate in more detail.


Roadgrip Airports Division and Runway Grooving Team.