I suppose that if a rail network wants to use regerative braking (especially if it has done for 40+ years), it might not want to be coupled to a grid with tight voltage & frequency constraints? Come to that, even the traction load is going to be pretty brutal, especially watching the sparks fly as the shoe bumps along our southern live rail. And all the wet leaves on the line… 

I suppose that if a rail network wants to use regerative braking (especially if it has done for 40+ years), it might not want to be coupled to a grid with tight voltage & frequency constraints? Come to that, even the traction load is going to be pretty brutal, especially watching the sparks fly as the shoe bumps along our southern live rail. And all the wet leaves on the line…