Isn't the problem here that 8 darts an hour need to pass each level crossing?
I'm no technical expert on what triggers level crossing gates to drop, but they would appear to lower based on distance from a crossing, even though there could be a station to stop at beforehand. So gates can be closed for several minutes before a train arrives. If 8 trains an hour pass by (4 in each direction), I'd estimate gates could potentially be down around half an hour out of every hour.
A system where the the dart driver can request the gates to be lowered between the station they're at and the next dart station would seem to me to give the advantages of:
- reducing the time the gates are down, leaving traffic more time to cross
- natural priority when they are ready to go.
Obviously, an even better alternative is to build bridges / tunnels and do away with the crossings altogether, but this may not be given a huge priority at the current time.