Why Does Road Construction Take So Long?

It's road construction season! On the first of June, I found that the interstate, the old highway, and the railroad on my daily commute are all undergoing maintenance, repair, and/or expansion. Only time will tell which will take the longest, but I would bet money that the railroad is the first project finished. What exactly are they doing on the roads every day, and why does it take so long? There are a lot of important factors involved in building a safe road that will last long enough to justify its expense. Practical Engineering gives us an overview of the nuts and bolts of road construction projects. (via Digg)