The junction layouts at each end are very tight and constrained with little opportunity to ease them without either impossibly expensive widening of the cutting or shortening or even abandonment of some of the platforms. Platform widths and positions and curvature across the layout cannot change easily either due to positions of columns supporting the buildings above. Signal spacing is very short with the mid platform signals, but is not substandard. The spacing is correct for the permitted speed, by engineering standards of the past and today. Entry signals are cleared under a modern equivalent of 'warning acceptance' when the far end of the platform beyond the mid platform signal is occupied by another train. Under modern TCB, a warning route only clears when the train has been brought under control approaching the authorising signal at red. A warning route normally has a shorter 'restricted' overlap (typically 50m) proved clear beyond the destination signal, but there are provisions in standards to omit this where speed is low and risk is assessed to be low, as must have been justified at New Street when the current signalling was designed. Whllst interlocking controls are unlikely to be significantly non-compliant, signal positioning and sighting may not all be optimum by modern understanding. Realistically, however, when the layout gets resignalled at some point, the signal positions are highly constrained by the track layout and standage required in the platfroms, so the only way to improve sighting (if it was considered substandard in any specific case) might be to provide additional co-acting signal heads (for short range viewing) and banner repeaters (for longer range approach viewing).
