The font family was originally called Underground, it became known as Johnston’s Railway Type, and later simply Johnston. It comes with two weights, heavy and ordinary. Heavy contains only capital letters. A further change occurred in 2008 when Transport for London removed the serif from the numeral ‘1’ and also altered the ‘4’, in both cases reverting these to their original appearance.
—from the wikipedia article on the typeface ‘Johnston’ which is the official typeface for the London Underground
