[nito]

The biggest barrier to frequencies is the quality and type of signalling, grade separation, rolling stock acceleration and deceleration, and platform availability for turning services around. It is why you can have non-metro railways that can and do operate at higher frequencies than bus routes and light rail lines.

Many countries have been deploying the European Train Control System (ECTS) to provide automated or automated aspects on non-metro railway lines, particularly where there could be a mixture of services (e.g. rural and intercity). Such upgrades can deliver higher frequencies and faster operating speeds, at the same time as increasing safety.