I have been researching the road for the past year or so. Sometimes things are not obvious. Big trucks may not leave big ruts from the tires but if you have stood on the road while one of the big trucks have passed you can feel the ground shake or vibrate a little.
this is not the single problem with the road but one of many. It does however contribute and is part of a cumulative effect. I think robvee will agree with me.

Here is an example for those interested in reading more. when the trucks pass it is like a mini earthquake.
http://en.wikipedia.org/wiki/Soil_liquefaction