It depends on what you mean.
I can’t speak for everywhere as even within a classification there are variations of design.
But most crossings that operate automatically (that use conventional signalling type control circuitry) use at least one treadle for each line and for each direction. Normally in combination with a track circuit or they use two treadles. Operation of the treadle (either one if two are fitted) or the track circuit will cause the crossing “close” sequence to commence.
Modern “overlay” Miniature Stop Lights (MSL) systems such as VaMoS types use axle counter heads instead.
For the area where I worked, if the line has signals, normally for user worked crossings with gates where vehicles could cross, you would have a controlled signal rather than an automatic signal to protect the crossing should the signaller need to. It may not be the same elsewhere.
Originally most of these crossings would only have had signs. Or would have been provided with telephones. Occasionally a “white light” may have been provided to indicate when it was safe to cross. This was driven from the interlocking.
Some were upgraded to become AOCL or MSL or similar.
Because the line is signalled, normally if the crossing uses conventional signalling type control circuitry, the crossing will use the same track circuits (if provided) or axle counters (if provided) as the rest of the signalling system. And as stated above, one or two treadles per line / per direction.
These crossings may or may not be interlocked with the signalling. It depends on the circumstances.
The arrangements may be different elsewhere.
For foot crossings, normally controlled signals were not specified. Hence you will find the nearest signals may be automatic types.
Overlay MSL systems such as VaMoS can be used where there is no signalling, or where there is signalling. In the later case, they are completely independent of the signalling. But if there is a signal near to the crossing or a station where trains are likely to stop, that adds complexity.
The subject of level crossings is complex because the requirements change over time and hence what was considered okay years ago is no longer appropriate. Hence many crossings have been upgraded.
The railway dislikes mechanical treadles as they require regular maintenance, the arms wear and they don’t like excessive vibration. But a working treadle is not affected by the problems that affect track circuits (contaminated rail head).
