With conventional colour light signalling, a mixture of 8 and 12 coach trains, and its flat junctions at Blackfriars, Thameslink in London achieves up to 16 trains per hour today on a single pair of tracks. With ETCS and ATO, up to 24 tph are planned in future on Thameslink and on the LUL subsurface lines (Circle, District, Metropolitan, H&C) LULs future signalling is claimed to be able to deliver over 30 tph through the complex inner circle network, with all its flat junctions. It is a mystery why capacity through the 'Valley Lines Core' is so constrained comparatively, considering that the local trains are typically shorter, even, than London's deep level tube trains, some of which are running at up to 33 tph on the Victoria Line. Clearly signalling in Cardiff is not optimised for capacity today. ISTR the 'home signal' overlap at Central for trains coming down the bank from Queen St. was extraordinarily long, extending at least part of the way along the one platform available for trains from that direction, and that meant trains would have to wait at the top of the hill before approaching a clear platform. Applied during the 1960s resignalling, the purpose of that exceptional safety measure was to protect passenger trains loading at Central from heavily loaded unfitted and partially fitted goods trains descending the hill behind them. With the remaining freight on the route now fully fitted, I expect the replacement signalling will be better for capacity than this, and there will be two platforms available to accept down trains in the future as well. In the up direction (towards Queen St.) one platform will have to suffice, but traditionally permissive working was always employed there to keep things moving. A train could enter the platform whilst the previous one was departing. This was a sensible use of the long platform considering trains are relatively short, and particularly useful for trains entering service from the depot which could be brought out empty behind trains already in service. Today such methods are frowned on using permissive signals, but the functionality can be replicated using mid-platform signals, as implemented today on Thameslink. An ETCS overlay, as being built for Thameslink, could allow an even greater throughput. With a new fleet planned for the Valleys and new computer based signalling about to be commissioned, a limited ETCS/ATO overlay to vastly improve capacity and performance through this important corridor should be possible.