Britpick Question

[amberfocus]

 I know that some of the smaller words like a and the are often not used in some of your speech.  For example you use "go on holiday" as opposed to "go on a holiday" or "went down the pub" instead of "went down to the pub."  Here in the states when referring to our freeways by name, we would say something like "get on I-5" or "get on the freeway."  For your motorways do you say "get on M4" or "get on the M4?"  Also would "get on the motorway" be correct?