Ok, I found the answer. That is if you believe the government...... This came from the Washington State DOT
What are the two sets of three grooves in the right-hand lane where holes have been drilled and then patched? This is on parts of I-90, I-5 and I-82.
In answer to your question, here is a quick summary of the work that has been going on I-90 and other concrete roads around the state.
I- 90 is a concrete roadway that has exceeded the original design life of the pavement (30 years). However, predominately the concrete is still in good condition, except for the roughness of the ride. The roughness is caused by "faulting" in the pavement. Faulting is where each panel of concrete tilts and leaves a bump when you drive on to the next panel. This faulting generates the characteristic thump-thump-thump you probably have experienced when driving on some concrete roadways. Each of these bumps can be as much as 1/2 to 3/4 of an inch, and every 10 ft. along the roadway. For trucks, the faulting will rattle your teeth.
To correct the ride, we can grind the pavement smooth again, but once the faulting has started, it will continue. Therefore to stop the faulting, we put dowel bars longitudinally across the joint where the faulting has occurred. We put 3 bars in every wheel path, buried half way through the concrete slabs. Once these have been placed the bar is grouted back into the pavement. The grout is a slightly different color than the original pavement, and as you drive across the pavement, would appear to be a groove in the pavement in the same direction as traffic. The color is different, because we use a special epoxy grout that develops strength within 24 hours, instead of the usual 2 weeks. The dowel bars stop any continuation of faulting, and then we grind the pavement smooth. This is only a temporary fix, but from other tests done, we expect a minimum of 10 years of added service to the roadway.
The faulting is always worst in the right lane, since this is where 75% of the traffic travels. Thus the dowel bars are usually only needed in the right hand lane.