One important point is the difference between passenger and freight-only lines. A freight-only line does not need facing point locks on points, can have shorter signal overlaps, does not need catch or trap point protection from sidings, etc. Subject to the usual weight and gauging restrictions, a freight train can run on a passenger line without further ado, but special measures need to be taken when a passenger train runs on a freight-only line.
This is as it was in my time and I doubt if the basic principles have changed much. However, I think that it is far more common nowadays to use equipment and designs to passenger standards on freight-only lines than it was.
Things have changed slightly.
But first a correction. On a freight only line, no signal overlaps are required.
On a passenger line, in certain circumstances, a reduced overlap may be allowed. Such as station areas where the line speed is low, and there are points/junctions close to the station.
Some freight lines are provided with signalling to passenger standard if the line may be used for passenger train diversions.
All new power operated points are now provided with a FPL as standard. Existing power operated points may also have been upgraded with a FPL. In most cases, this does not apply to existing mechanical points operated from a signal box or ground frame.
Indeed, some point equipment has to have a FPL as it is an integral part of the equipment. Such as RCPL (Rail Clamp Point Lock, or clamp lock for short).
In the past, trap and catch points were required because unfitted freight trains were permitted (trains that did not have a continuous vacuum or air brake). But now, the preference is to remove as many trap and catch points as possible (less maintenance, hence cheaper). So, you will find freight lines without trap and catch points.
Trap points are still used where there is a risk of a runaway wagon or locomotive joining a running line, such as at the exits of depots or sidings.
Doesn't line speed determine the maintenance regime for any particular route?
Things like frequency of track and structures inspections, tonnage carried, signalling standards, level crossing specifications, platform clearances etc.
There seem to be jumps in standards at 75, 90, 100 and 110mph, with a different set applying at 125mph.
HS1 (and HS2 in time) are different again (and are not part of NR).
Some inspection and maintenance is done at a defined frequency (number of times per year) regardless of the line speed or the traffic level. Signalling maintenance is a good example of this. The maintenance happens at the defined frequency even if only one train a month runs.
Network Rail does have a classification system. But I don’t know if they publish the details in a public area. For example, the GWML has a classification of level 2 between Paddington and Bristol T.M.. But beyond Bristol T.M., that same main line is classified as level 3, as it’s considered less important.
Passenger “branch” lines may be classified as level 4.
