You're in Stockport! I have some railroad friends in Stockport, and I've taken the time to do similar kinds of shoots.
These are vastly better in sharpness - I think this is what is representative of what the hardware can do. There are sharper lenses, but as you can see it takes technique to exploit them, and even so most of those sharper lenses are only somewhat sharper at these apertures. There's still a little more that can be gotten out of your current gear, but this is probably 90% or more of what's attainable.
I suspect that you don't need a tripod at these shutter speeds and lenses to get very close to this sharpness. Your lenses have VR, and if you're using it (and allowing the VR to settle before releasing the shutter), you'll get probably 98% of this sharpness most of the time. If you're planning to make a big - really big - print, go for the tripod, but if you can maintain the parameters in the safe area, hand-held will certainly do very well. If the light goes down, though, a tripod will be a major improvement.
As far as exposure goes, I think you're a bit hot (overexposed) on some of them. For example, 0927.jpg is almost certainly a bit blown out. (I'm on a marginally calibrated monitor so I can't tell for sure, although I doubt it's too far off.) In that one it looks like you've opted to preserve shadows at the expense of highlights. That's a valid choice but I don't think it's an exclusive choice on this image and probably on this one I'd have opted differently as there are a lot of highlight areas that are very distracting. I shoot raw and thus have more latitude to process, but I'd go into Lightroom and try to recover those highlights. You may or may not be able to do that with a jpg.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!