Pelican Parts Forums - Why perpendicular ridges on the fwy?

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Copied from the internet at https://www.quora.com/Why-are-lengthwise-grooves-cut-into-highways:

Quote:

[Poured concrete] surfaces are usually given some kind of roughening up while still plastic. In the past heavy bristle broom finishes were applied but those also wear down within a few years to a dangerous level. The best surface for providing a long lasting friction level is to use metal rakes that form a “tined” surface of grooves approximately a half inch apart and about 1/8″ deep. These can be placed either transversely or longitudinally. Both are essentially equally effective but aesthetically most people prefer transverse.

Even though that tined texture will last quite a few years a heavily trafficked road will eventually need restoration of it’s friction to remain safe. One way to restore friction is to grind grooves into the pavement surface to restore the macrotexture which improves friction. Grinding can be done transversely or longitudinally. Most of the time it’s done longitudinally because that’s the only cost effective way to do the work on a road which needs to keep most of it’s lanes open to traffic while one lane is worked on. Trying to do it transversely would be very expensive because you’d have to close two lanes to have room to work on one and you would be stopping and repositioning the equipment every few minutes instead of just taking off down the lane and doing continuous grooving.

Quote:

Originally Posted by Porchdog (Post 10321504)

So here is the theory -

Traction on concrete is mostly controlled by "micro-scale" roughness. The problem is that at this micro-scale the concrete pretty rapidly gets polished by the action of tires, then acts like a terazzo floor.

By cutting those grooves the wear of the concrete is continually exposing rough concrete going down the sides of each groove.

The large grooves aren't only annoying with sportscars, motorcycles and some tread designs - they reduce the traction surface under your tire contact patch. The highway engineers have decided that the longer maintenance interval is worth it.

They used to use a rough "broom" finish or similar - but that ends up polished more quickly. When the travel lane is so smooth the Joe Public is hitting the guardrail in every rainstorm, the highway department needs to do work.

So the grooved surface wears a bit faster in terms of inches per year, but it maintains traction longer.

Good explanation.