[Talk-GB] maxspeed field - what units should we use. etc

[WessexMario]

I propose that we adopt a new key:  maxspeed_mph

It would be

- simpler for UK, USA and other imperial countries to enter the speed.

- less prone to error - users may not be used to kph speeds.

- un-ambiguous.  (what does '50' mean?)

- maxspeed keeps consistently metric units (kph)

- exact - being in the local units, no rounding necessary (no decimal 
places).

- value will usually only be an integer in a multiple of 10 or 5. - easy 
to validate.

- both maxspeed and maxspeed_mph keys could be entered - no ambiguity again

- applications can easily convert between maxspeed and maxspeed_mph 
where only one is entered

- in transition, having a separate key would make it simple for 
validators (people and computers) or a batch process, to convert 
existing maxspeed keys in the UK and USA from the various existing 
maxspeed variations to the expected multiples of 10 in maxspeed_mph

Mario
(WessexMario)