"The answer, according to Pennsylvania Turnpike Commission spokesman Carl E. DeFebo Jr., lies in the special conditions presented by the construction zone.
In order to keep traffic moving as efficiently as possible during repairs, engineers sometimes route vehicles temporarily onto road surfaces not designed for full-time traffic, DeFebo said.
For instance, when driving on temporary lanes through a construction zone, you might actually be using what's normally the shoulder of the road, or a stretch specially built for use only during the work, he said.
As the Warrior has reported previously, roadway "shoulders" are not as deep as main travel lanes, the subsurface materials vary, and other differences make them unable to sustain heavy loads or lots of traffic without failing prematurely."
source: http://articles.mcall.com/2003-09-05/news/3485580_1_lane-concrete-barriers-roadway
