The whole idea makes no logistical sense. Roughly a dozen stops per trip, leaving out all larger parcels. So you send out a guy to an area that is a half hour round trip to run off a few side streets? All while bringing down the image of UPS where a kid jumps out of a beat up Civic with your package? At the worse, this may happen for peak, but not year round.
If UPS wanted to, perhaps they could've implemented permanent on car helpers year round where drivers would be doing 250 stops year round and you could drop 1/3 of routes. There's a reason the union hasn't allowed this type of tactic.