The canal bridge in Inverness has a two aspect protecting signal, but a recent report into the crossings on the FN/Kyle lines (it's an ongoing point of contention) said that the ideal solution for the busiest roads (eg Dingwall) would be MCB but said this wasn't compatible with RETB.
As a long-suffering commissioner of signalling upgrades I'm entirely used to reports telling me why something can't be done! Of course, people once said RETB would never work, but BR boffins went ahead and invented it anway - and saved a number of rural railways in the process
I can see why they'd say that at Dingwall, though, where RETB block posts are proximate to the crossings. And it's true that MCB crossings aren't directly compatible with RETB, but that's not the same thing as saying you couldn't have a separate crossing panel in Inverness box working MCBs remotely.
Here's a solution: approach distant and stop board in each direction, not interlocked with the block sections. Driver or treadle activated barrier sequence. CCTV cameras and lighting fitted along the route with a DOO-style monitor-bank by each signal. When barriers are down and enough time passed for vehicles to clear, a white light shows authorising driver to move if all monitors are clear. Driver then drives on sight under "tramway" rules. Simples!
But the expense would be huge. I guess I'm saying what's *technically* possible, which isn't to say they are affordable solutions!