Pourquoi "sur" et pas "dans" pour "les lignes RER"?

Question

Les autres modes de transport utilisent "dans". Un wagon du métro et un wagon du train sont similaires. Cependant, le métro utilise "dans" et le train utilise "sur". Pourquoi?

Accepted Answer

Bonjour Nancy,
Here's a link to a similar question: Why is 'dans le train' correct but 'dans le RER' is not (it is 'sur le RER')?
I hope this is helpful.
Bonne journée !

Answer

Le métro has come to mean the ‘tram/train’ as well as to be an abbreviation for ‘le Métropolitan de …’ - the system. As in previous answer to Kathryn, my understanding is that if talking about the ‘vehicle’ which is the actual mode/means of transport - le train, le métro - dans is used; if talking about a transport system in general rather than a specific vehicle - les lignes RER, le Métro de Paris - ‘sur’. You don’t travel ‘in a system’, so ‘dans’ doesn’t fit.