Sidewalk Closed. Detour Plan: Run!

Would a construction crew walk out into the middle of an intersection & drop "road closed" signs without plans for detours?

Then why would a crew in Arlington start jackhammering the sidewalk at one end of the heavily used Sycamore & 17th St crosswalk with no pedestrian detour?

I've talked to Arlington County Board members & staff about issues like this before and I know it drives them as crazy as it does me. But it would be nice if the road crews got the message as well.