system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why did it take two years to construct the old World Trade Center and 13 years to construct the new one?

The original WTC1 was built between 1968 and 1970.  Even if we're generous, the new main tower started construction in earnest in 2006 and will "open" in late 2014.  I'd think things would go faster with improved technology. What gives?
gpt
The two years of construction you cite for the original towers don't include planning and design work, which can take many years for such a large structure.

The new building also had to wait until the entire demolished substructure of the old buildings was removed and replaced.