What are the orange circular prisms mounted at various places around railway and underground tracks?

Question

They seem to be circular orange pieces of glass about two inches in diameter and held in a metal mount. They appear to have been mounted very precicely (at almost right-angles to the track). In the underground they are on the tunnel walls but in the main-line stations they seem to be set at track level. They are probably about 10 yards apart. I see them everywhere! They can't have been cheap to install so they must have some importance. I wondered if they were some kind of surveyors tool to detect minute amounts of movement.

Answer 1

if you mean a white disk with red line across it its a shunt signal otherwise give us more info

Answer 2

An Orange Circular Prisim? I am not sure where you are seeing these, but never come across these at all in the 13 years I have been working on the railway or in the Rule Book for the DC Lines area. Could you elabarate as to where you have seen them?

Answer 3

Hi there the Orange Circular Prisms that are mounted arround the railway & the underground are surveying equipment that are monitoring the ground movement in the stations & track.

I have been working at Kings Cross for the last 2 years and we have them set up because London Underground are building underneith Kings Cross Station a new ticket hall which will have easyier access to the platforms for disabled people & will also have direct access to the new Western Concourse that is being built by Network Rail along with the refurbishment of the Victorian Station.

I hope that my answer helps.