QUESTION: "I can see why there are no U-turns allowed on toll roads but why can't we make a U-turn on a road like 89 or 91? It could save fuel for some people."
Good question - It really boils down to it being a "Safety Issue." Troopers and Highway Workers receive specific training concerning the proper way to take a U-Turn on the Interstate and/or how to pull out of one.
While there may be a few drivers out there that could and have successfully made a few in their day the far majority do not take into account the factors, skills and dangers involved and it results in a collision. Now plug in "The Human Factor" - someone coming too fast when you're pulling out and they didn't "appear" to be coming that fast, someone driving in the dark with no lights on, a DUI, etc. etc.
For the Troopers it involves, but "is not limited to" this short list:
I investigated a collision involving a Trooper pulling out of a U-turn on an icy morning, blue lights activated, with a line of sight of 1,000 feet. He had received a call of a truck up-side-down in the middle of I-91 in the southbound lane in Dummerston. He was traveling north, so hit the first U-turn he could find. He saw two vehicles coming from that distance, both in the right-hand lane. He started to accelerate, under the conditions. The driver of the second vehicle back decided to pass the first one, caught up to the Trooper and decided to pass him also when the Trooper's vehicle was going into the passing lane, blue light still activated.
AOT Trucks have to be even more careful. While they have all the emergency lighting they are slow and careless drivers overtake them quickly, failing to heed all the warning displayed.
A current example was posted by Maus Anon E here on iBrattleboro.com on March 24, 2008, when a Tractor Trailer operator "attempted his U-turn on I-91 in Vernon. Click on the following hyperlink story entitled: "Smooth Move Near Vernon." (Annikee, ConductorChris, CrankyYankee, Maxwell_Edison and MMulligan all responded!) I remember the photograph in the Reformer showing a vehicle, that was northbound, under the trailer. The Truck Operator was charged with Careless & Negligent Operation, amongst a bunch of other tickets.
The short of it - don't make U-turns, not even on streets and other roads - You're "An Accident Looking for a Place to Happen!"