with regard to launching from a steel bridge, if I were going to do it one thing I would be mindful of would be the possible interference with GPS signal and take care with regard to the home point being updated. I would also return well before the battery was very low. If you can launch legally you can fly legally, for the most part. Along with Chugach State Park views, I launch from the highway next to Denali National Park. I only encroach a very small bit as I might circle around a river that borders the park but I do indeed enter the park if only by a few hundred feet and am confident I am doing so legally. If the middle section of the bridge is not part of the park it would seem to me (IANAL) legal to launch. I would note that the B4UFly app even shows the middle of the bridge to be outside the no-fly zone. You would, however, only be able to fly around that center section as either end is off limits.Brilliant!
Not trying to resurrect an old thread but what about take off and land on the bridge itself? The map clearly shows the middle section of the GGB is not part of the GGNRA. Sure you have to get there carrying your bird via the pedestrian walkways, but if too far to walk, one can always ride a bike LOL.