In the US we must carry driving licences when driving. (Whether you live there or visiting from abroad). I find that very odd here that you don't. Considering an accident, the one at fault can just scarper after exchanging false details if they have a record! When there is a need to stop a motorist for accidents, speeding or a breath-check, you must produce your licence to show you have a valid one.
For ID purposes, the US state DVLA equivalent issues non-driving cards with the same details and the database is kept by them.
That way if you do not have a passport and want to do banking, sign contracts, buy booze if you look underage, you can produce this and it's an official ID.
Why not... with identity theft such a problem, I think it should be put into practice.