FWIW, having the relay receive a bit more voltage, within reason, is not really an issue for most relays. In intermittent duty, getting 15-16 volts on the coil shouldn't be an issue.
For 18V track voltage, I've found half-wave rectification and a decent filter cap (I use 220uf for small relays) has done the job for us. I do add the small value resistor to limit inrush current and arcing at the rails, and the 22uf choke for DCS compatibility. Yes, I power the relay from the rails, it's way more convenient for a modular setup than trying to run separate power.
