Wrong Way?

I took this picture inside the large 'train shed' in Bristol Temple Meads, with the tracks through the 'train shed' behind me and the main entrance beyond that. The archway labelled 'Way Out' therefore appears to be leading in the opposite direction from the station exit. The probable explanation is that there is no access to the subway from the platform I was standing on, but if my assumption that the platforms outside the 'train shed' are a later addition is correct how did passengers cross between here and the station entrance before the extra platforms were built?

Done