Doubling someone’s commute diverts more of their money into commuting expenses, which removes that exact amount of money from some other category of spending.
If diverted from savings, this grows current GDP. If diverted from some other category of spending, it’s likely neutral. (If diverted from higher velocity domestic spending into the importation of energy [and exporting of cash], it could even shrink GDP.)
If you double some poor saps commute that grows GDP too.