So my in-laws were on a long car trip this last month and when they got to my house they asked me a question, what are thise weird grooves on the highway all about? I’ll try to explain this as best I can.
Sometimes on interstates there aregrooves in the road, Usually in groups of three, spaced about where your tires are. They are superficial but visually noticable, they seem the be spaced in a group of 3 and then a long break and then spaced again. These aren’t the same thing as the raised bumps used to indicate the sides of the road, these are right in the driving lanes. What are these for? They seem spaced too far to be for snow tracktion or rain runoff, they don’t seem to make any noise when you drive over them.
Here is my attempt at a visual example on how they are spaced (imagine the distance between the 2 sets is maybe 50 yards or so:
I have no cite but I’ve been told they are for drainage and to increase tire traction. Something about keeping cars from hydroplaning all over the place
The patent (United States Patent 4701069) for the machine that cuts the grooves explains that it can be used to create markers (rumble strips) or draingage grooves for rain.
Though I haven’t seen that particular arrangement, I believe my distant cousin NotSpartacus has it right. The grooves allow the water to escape from beneath your tires, and you can keep your car from acting like a two-ton waterskier. The more usual method of grooving the whole surface causes some motorcycle tires to wander. Perhaps this new arrangement is kinder to two-wheelers. That’s a guess.
They have a similar sounding set-up on many highways in Ontario (well GTA and 401 at least), however they are on the side of the highway, on the shoulder. I understand that it is to warn you if you are going off the highway (wake you up or whatever). Perhaps a similar reason?
No, none of those reasons are correct. (This was actually the first question I asked on the SDMB, years and years ago.) The slots are for supporting load–they’re not actually grooves, per se, but they’re slots cut in the concrete. A metal dowel is dropped into the slot and it’s then filled back in. Here’s a description of the procedure (scroll about halfway down to “Load Transfer Restoration”).
There’s a nice little diagram of the dowel placements, too.
I think we all talking 'bout two different things.
There are roads where rain grooves are just rain grooves, and wherein the machine used to cut those grooves was used with the intention of making rain grooves.
zut is correct about the grooves as described in the OP. Rain drainage grooves are continuous, not interrupted. Older concrete highways were too smooth and planing could happen. Newer highways are finished with a much rougher surface to accomplish the same end.
As to the load transfer devices, the expansion joints in the paving are a way for water to get under the concrete and soften the soil. It’s the ground that supports the concrete. When the ground gets soft at the ends of the section at the expansion joint, loads on the end of the paving block, such as a truck, will pump the soft, waterlogged soil out from under the roadway creating a cavity. Then further loads will break of the concrete creating more places for water to get in and eventually the whole roadway section breaks down.
The load transfer devices make both sections of roadway on both sides of the expansion joint share the load and that greatly reduces the flexing of the roadway under load and this reduces the pumping.
I was once parked alongside a concrete highway on a sopping wet day near an expansion joint. A semi went by and mud and water flew a good ten ft. high out of the joint.
Many of the freeways in the Seattle area are grooved. There are signs that warn of the grooved pavement and that it is for better traction in wet weather.
I asked a VDOT person about what I think you are describing. He said that they were to indicate a change in speed limit, or a dangerous spot in the road ahead.
has it right. The grooves allow the water to escape from beneath your tires, and you can keep your car from acting like a two-ton waterskier. The more usual method of grooving the whole surface causes some motorcycle tires to wander. Perhaps this new arrangement is kinder to two-wheelers. That’s a guess.