In Cambridge Summer 2003 TT 6E87 enters Papworth Sidings at 12:56 for Ely Reception on down line. To get 6E87 into Reception route must be set from 278 to 762 or 764. With route set through Ely platform 1 between 290 and 278 trying to set route from 278 to 762 or 764 gives ‘No overlap available’ message. I had to wait for 6E87 to stop at 278 and the overlap to time out before I could set route from 278 to 762 or 764. Is this the way it should work? If yes, I'd be interested to know why.

In Cambridge Summer 2003 TT 6E87 enters Papworth Sidings at 12:56 for Ely Reception on down line. To get 6E87 into Reception route must be set from 278 to 762 or 764. With route set through Ely platform 1 between 290 and 278 trying to set route from 278 to 762 or 764 gives ‘No overlap available’ message. I had to wait for 6E87 to stop at 278 and the overlap to time out before I could set route from 278 to 762 or 764. Is this the way it should work? If yes, I'd be interested to know why.

I don't know this one, but there are other places where it happens - for example Up slow at Alexander Palace you can't set the route to the GL until the TC has cleared. Similarly the crossing from the Down to reversing siding at Bedwyn (on Westbury) has to time out. I believe that it's because the point is too close to the signal/too slow should a SPAD occur.

jrr

The stuck points are normal when routing to a siding or goods line. I speculate this is done when a train spading at track speed would be a dangerous scenario. Such as a train going 50 mph on to a 10mph goods line with catch points.

Talking generally, an overlap is 200 yards long and needs to be proved clear of trains before the signal reading to this signal is allowed to clear. If the pointwork leading into the siding means that there is less than 200 yards of track proved clear then the signal cannot clear. Other reasons include the cost of providing a swinging overlap (can be very complex in interlockings) was too much for a move that involves a near-stop at the signal anyway, so little cost-benefit.

Thanks chaps. That all makes good sense.