The problem is that the time to wait for the signal to turn green starts taking longer and longer and people will start to ignore the signals. I see it all the time with pedestrian signals. That is, pedestrians will just start crossing on the don't walk sign rather than waiting for the next 2 minutes before it changes. The same thing will happen when the red phase starts taking more than a minute to change to green or people (whether when in a car or on a bike) will start running the red lights more if they know they're going to get stuck for multiple minutes at the signal otherwise.
https://austintexas.gov/news/new-central-austin-bicycle-sign...
http://fitness.blog.austin360.com/2017/08/04/new-bicycle-tra...
But I should note that those cover only a small fraction of the intersections with this problem in Austin. So few that I've never seen them and I ride a bike on a daily basis. I have been on many of the mentioned streets, but I must not have gone through those intersections as I would remember a special bike light.
(Plus, you can see a few cars parked in the bike lane in one of the photos in the second link. So much for respect for cyclists...)
The separated lane along the Drag sucks (which is the one in the photo) for the reason you mentioned -- cars will turn across it, and people will wander across/along it.
The two-way separated lane on Rio Grande is great. My only complaint is that I occasionally come face-to-face with a car that decided they wanted to use it.
There's one of those bike signals on Rio Grande and 24th does make that light slow, and people ignore it a lot (partly because it's West Campus and that's what kids so.) It's also very short, at least when going north. It's green for long enough to get across the street, and that's about it. Once it turns yellow, cars to the right of the bike lane get the left-turn green. It just miss that light and have to wait a long time roughly every day.
I think better than the signals may be the "I see you" signal on southbound Rio Grande and MLK. There's a blue light that will light up when it detects you, so you know you'll eventually get a green. Going the other way, and at many other intersections, at certain times of night, I know that I have three options:
1. Wait for a car going the same way as me shows up and is detected,
2. Bike up onto the side walk so I can press the pedestrian signal, or
3. Run the light because it doesn't know I'm there and it will let me wait indefinitely until one of the above occurs. (Or morning rolls around in 8-12 hours, I guess?)
I'd trade all these new bike signals for more of those detectors/blue lights. Maybe all the intersections will detect me if I stop in just the right spot, but I don't know what spot is for any given light.
That's a significant design failure. In my town, they have been adjusting those embedded road car detectors so that they are sensitive enough to detect bikes. You do have to sit on the right spot, but they've added road markings to let you know exactly where you have to be.
Another side of this puzzle is that we don't require drivers to update their education or competence on a recurring basis. If we required all drivers to update their education and demonstrate their physical fitness to drive safely every couple of years, this would all go more smoothly.