Q.: The concrete pavements in the central part of our village are serving remarkably well in spite of their 1940s vintage. We don't have much cracking or faulting, but they are worn smooth in the most heavily trafficked areas. We are thinking of safety grooving. Does grooving have to go across the pavement to give good braking and resistance to skidding, or can it run lengthwise, as on expressways? How far apart should the grooves be spaced?
A.: Longitudinal grooving is effective in improving both braking and cornering friction coefficients. It is reported to make a wet pavement perform almost as well as a dry pavement. You can get a variety of recommendations on groove spacings, depending on whom you consult, but there is good evidence that spacings ought to be 1 1/2 inch or less.