Dave,
Thanks for the idea. Although this idea would increase the difficulty of programming, I suppose staying alive is worth the extra effort.

That said, I am going to try and build upon it and keep brainstorming this. Personally, I am not going to have a reed switch right away so I will have to press the button again to shut off and have a time factor (~2 min I think) as a backup shut off.
With a reed switch, you are absolutely correct, one would turn on a turn signal 1000 - 2000 feet before the turn (in the country). So lets think through how to make this work. We are cruising at 55 when we turn on our signal. At this point, we are only going to slow down until we make the turn so we can say
Keep the signal on as long as we are decellerating. At this point one of two things will happen, we will either come to a stop or we get the green light and can go on through so how do we account for that? How about
upon acceleration, go 500 then shut off. Okay so now we are stuck in traffic. Our turn is coming up but the cars in front are stop and go. At this point, the signal will shut off every time you move forward 10 feet. Now given that the slowest road speed generally encountered is at schools at 20mph and that is also about the highest speed through a 90 degree turn. So instead why don't we say
Upon acceleration AND a speed greater than 20mph, go 500 feet then shut off. Now our distance limit will not initiate until we are in the middle of the intersection under most circumstances. The numbers can be adjusted easily to suit you normal driving conditions.
What do you think BS360. Do you think that is possible?