"A unique feature of the D78 stock is that it has tube stock sized wheels. Traditionally, surface stock has always had 1067 mm wheels, whereas tube stock has 790 mm wheels. In an attempt to reduce the number of different types of wheels sets in use on the system, the D78 stock has the same type of wheels as the 1973 tube stock.
"The D78 stock also saw the introduction of new kind of bogie..."
Maria is conscious of a low, dark, sinking feeling in her breast. She is an intelligent woman, a school teacher. She wants to see the history of England. Harrods, she wants to go shopping in Harrods and buy tweeds, though they are a bit hot for Guadalajara. Instead, she is travelling on every line of the London Underground. She hates the air, she hates the noise, she hates the blackness through the windows, perpetual night.
Then, as the train slows, her husband taps her arm to leave. She looks up in surprise.