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Birmingham New Street has a capacity problem.
If you create a minimal number of underground platforms, you can reroute local lines underground to create RER like North South and East West lines - basically what the underground Euston platform is for Thameslink.
You can easily have metro like services in the city core and 15-20 minute services out in the suburbs. Most importantly they will have line names and integration of city's new smart ticketing card Swift.
With a bit of investment in the outer city stations you can even have tube like regeneration effects where the city starts growing around the stations.
