Why am I running? Because it's one of the best workouts one can do for overall fitness. I do many other exercises, such as cycling, weightlifting and some crossfit and do a little recreational sports, such as frisbee, racketball...
But of all them running is vital, as I see it to overall fitness, simply because our bodies evolved to run as evidenced by our superior ability to run distance and they say that the Achilles tendon is specifically designed for running, not really needed for walking. Interesting article on that:
http://www.newscientist.com/article/...n-running.html
As for my planned run up and down the bridge not being
"considered a hill workout". I'll get back at you on that, personally I think it's a start, at least that's my impression now. I could workout on the machine at the gym that elevates to 50%, but I also need the downhill aspect also, that's why I'm using the bridge.
I don't believe anything you mentioned could replace hill workouts and I already do sprinting.