Would be even better as a tram

London's new bus would be even better as a tram, would it not?

Class 73 Jubilee

Gatwick Express Class 73 73208 Clapham Junction, originally uploaded by dwb photos.

It is hard to believe that it is fifty years ago since these locomotives entered service. They are 1500 hp electric locomotives running on the third-rail system and have an auxiliary diesel engine of 500hp. This makes them extremely versatile. Not only are the majority still intact and working, but there are plans to refurbish some to keep them going.

Whilst not the most elegant things on rails - apparently they are known as "shoe boxes", they embody the excellent principle that everything should be compatible with everything else on the system. Thus they could haul anything and could be controlled from the cab of all of the other multiple unit diesel or electric trains that were coming into service on the Southern Region at the time.

This strategy of compatibility continued until the early 1990s when new types of stock were brought into use which used entirely different control system. Nowadays, nobody cares about compatibility and many combinations of rolling stock cannot even be coupled to each other without the use of special connections.

The lesson should not need to be spelled out.