In Boston we have heard many reporters claim that the delays in the Big Dig (the highways tunneled under the city and the harbor) were increased by contractors stretching out the work to increase their incomes.

Not so much a planning bias as a pocket book bias.

I presume that (a) this is not the first time that contractors have stretched out a job; (b) the Big Dig planners FAILED TO EXPECT contractors to behave exactly as they ALWAYS DO.