Axle counters are track-side devices that monitor and count the number of train wheels passing by them - replacing semaphore signals and supplementing traffic-light signals by providing real-time train position information direct from the track-side. They form part of the new generation of secure and safe signalling systems which is being implemented across Europe within the European Rail Traffic Management System (ERTMS).
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The suggestion is in the event your phrase refers to the pneumatic lines placed across a road which count axles going over them, a pneumatic activated counter in the box senses and accumulates the number of axles passing over them.

this obliges them (whoever they are)to replace the present block signalling systems by means of axle counters.

Axle counters are devices on railway track that count the number of axles that pass over them to ensure a train is complete. Given that each vehicle has a pre-established number of axles, by counting and dividing it is easy to check that no wagon has got loose and run away. It is also a way of ensuring that the whole train has passed a given check point so that the line can be released for the next scheduled train. Block signalling is one way of fulfilling this function but is now being superseded by axle counters.

So I confirm the others were right but thought you might just like a bit more information from my years working on the railways

counts the number of axles which have passed over a given point