These are the link lines whereby international services leave and rejoin the HS1 line so as to facilitate a stop at Ashford International.
When the international services began, they operated to and from Waterloo Int’l, using standard lines through Kent as far as Ashford.
Accordingly, the trains were designed and built with the ability to inter-act with both HS and standard UK signalling operations.
This necessity was underscored by the route between Lille and Brussels, which – at first – also operated on standard lines. That situation was quickly remedied by the building of a special HS line through Belgium.
When the terminus was switched to St Pancras the only section of the route running on non-HS lines was the AS.
When the service operator started developing new generation trains to run the services, they took the (obvious?) decision NOT to include standard UK signalling compatibility. Therefore any service that operates using new rolling stock cannot, at the moment, call at Ashford Int’l. Ergo, as more of the new rolling stock is introduced, the options to call at Ashford will decrease.
If Ashford is to continue to receive international passenger services, to the clear benefit of passengers throughout Sussex and south Kent, then the AS must be re-signalled with HS infrastructure.
It is hoped that the status of the associated project will be clarified within the Chancellors Autumn Statement.