There was quite a bit of traffic on 89A the couple of times that I've been on it, but I've never been on it early in the morning. You're right chephy, that half mile seems long because it is up hill and I'm up against a guard rail for part of it.

On the I-17, I would be able to get off on the first exit I come to and ride the next two miles on a bike path into town. But it would be a lot faster to stay on the Interstate and get off at the second exit.

Yes, it is legal to ride on the Interstate here.

No, none of my commute will be in the dark (I'm hoping), and neither road is lit at all.

89A is two lane with almost no shoulder and the speed limit is 55 I believe.

Thanks for the responses guys! I might have to take a day off and ride up to 89A to study the traffic at the time I might be riding on it.