Construction cranes

I have been traveling the same path to and from a hospital daily for the past three days.  Along the way, there are two apartment/condo buildings under construction.  Since I am usually going after working hours, the construction crew is always done when I drive by.

My observation and curiosity is that I noticed when they shut off the cranes, they swing the booms out over a major Denver thoroughfare.  By the way, these are not the cranes where the guy climbs to the top and sits in it all day.  These are firmly planted on the ground and operated from the ground.

Why would the crew want to set the booms out over a busy street?  Is it in case they fall, they won’t damage the structure they’re building?  If they fell, they’d surely cause a major traffic accident, since that street is busy nearly round the clock.  Another question that will probably never be answered.

Construction question

I’ve noticed that in almost every construction job of any magnitude, when they’re prepping the ground to start building, a large hill of dirt goes up.  Why?  Is it dirt they’ve removed to level the land?  Have they brought it in from somewhere, and why?  Do they plan to use it later?  I’d love to know the answer.