Three comments on the LED traffic lights.
1) They use a small fraction of the energy that the normal ones do. Portland OR. replaced theirs, payback on cost was under 3 years. There are some energy ‘rebates’ tied to replacing the incandescent traffic lights with LED – don’t know the specifics on it. The reduction in energy costs ends up being a ‘recurring savings’ with a payout of about 33% on cost after the 3 year period due to energy savings alone.
http://www.portlandonline.com/shared/cfm/image.cfm?id=111737
2) The LED lights last a lot longer than the incandescent (claimed 3x as long – they must be stressing the LEDs, because it should be longer. I hope they are using a heat sink in the mounting for the LEDs). This cuts the yearly maintenance cost in a third.
3) Not all LED traffic light lamps are made in the US.

Eyeballing the costs. 4 way intersection, 2 assemblies per direction – 3 lamps each : 24 bulb assemblies – approx $100/per lamp = $2,400 in material. The $5000/per may be high, but it is near the ballpark. It could be the ‘fat lazy union-workers’ ;-P who pad up the bill with slow bulb changes – though I see that labor costs are taken out of the $5000/intersection.