Great Western Coffee Shop

 due to my cancelled London train,  well it wasn't actually, one-engine-only so does not stop at the station but
 flies ' effort-lessly '  up the through line.

 So spending time looking at the track,  an up and down line probably takes up less space than the normal
 dual carriage-way. I then considered the actual cost of one mile of rail track, installation and maintenance
 to the equivalent cost of one mile of a road.
 
  I suppose you have to take into account signalling etc.,  but could I suggest that advances in technology would make the
 system of lights/track circuits etc  obsolete.
 
 Any thoughts ?

I think that's the way it's headed - things line ERTMS ("European Rail Traffic Management System. A future railway signalling system, with equipment located in the driver's cab, rather than at the line side")

On extended trial on the Cambrian Coast line - all of the line side signals with operational bits have gone, replaced by static signs that tell the driver things (not ever sure if they're lit at night?) and there's clever stuff in the cabs. Still need point motors, I suggest (though most could be sprung on the line) and the need for the on-train fittings limits what can be used there now.

I am not a great fan of in cab signalling. It requires a great deal of high technology and is something else to go wrong, and unless every train in the UK is to be so fitted, it restricts what traction can use a line not equipped with fixed signals.

Network rail cant even get fairly conventional signalling to work properly in the Reading area, so I would not trust them to manage anything newer and more complex.

Despite this, it should be possible to build railways for a lower price than a main road. When new railways or roads are needed, consideration should be given to building them next to each other so as to minimise costs and disruption. As an example, the cost of an extra wide bridge to carry a road AND a railway over say a river, should be less than two bridges.