What more are you hoping to get from your footage? Protune or not? I think it looks pretty good. I could point out a few things, just suggestions take them for what they are worth. A couple of things I noticed and they are picky things so I wouldn't be too worried about them but it might give you some food for thought.
First did you notice at around 28 seconds or so and as you panned around with the sun in front? Your shutter speed wasn't locked in and during that short time you were facing the sun the footage got a bit shaky. Your shutter speed ramped up to compensate for the additional light. Higher shutter speeds that more than double your frame rate causes additional shake, jello, etc. things I'm sure you already know. Its little things that you can pick up to jump to a higher level of editing and shooting. It was brief but it was there. So I like to set my shutter speed manually at 1/60 second when shooting at 30fps. Its much easier when the light is lower like you where shooting in.
You may even consider shooting with no ND filter in lower light like this to help keep your ISO at its lowest possible setting. The GoPro is actually not too bad up to say ISO 800 so other than a little shadow noise in the bride pylons and at the 1 to 2 minute mark the shadow areas to the left of the train tracks, your noise levels look good.
Look at how your shadows and sky exposure looks when the sun is coming from behind the camera. Actually it looks nicely balanced and your GoPro colors look nice and your white balance looks good. When you are facing toward the sun the shadow areas tend to wash out a bit and look blocky, and your color gets a bit flat. Its part of dealing with small sensors and digital sensors with smaller exposure latitude. If you are not in Protune going to it can help you in those situations. You have more latitude available in both shadows and sky. Remember you can still use GoPro color even with Protune on so if you aren't into color grading yet you can still get nice results.
I ran a sports photography business for many years and one of the first lessons you learn is watch your backgrounds. Look at your shoot and ask yourself how could I eliminate backgrounds that may not be favorable. What if you would have shot the train from the other side of the bridge by the golf course? You would have eliminated a road and housing development. It would have looked like you were in a rural area. One of the other lessons you learn fast is the have the sun at your back whenever possible. You reduce shadows, bring nice light on your subject and reduce flare issues. That train shot from the golf course side with the sun at Solo's back and shining on the train would have really made it pop out.
I think what you shot looks very nice, and your settings look like you are right on track. I know you weren't looking for critique on your shot but how to improve settings. But The two really do go hand in hand. Hopefully that is the feedback you where looking for? Some of the other talented shooters here may have more for you. Nice work, you should be happy with this footage!