Gatwick Airport said it would ensure road congestion would not worsen if its plans for a second runway went ahead.
The airport announced plans to improve its public transport links on Monday (June 2).
A spokesman said: “The airport will be road ready for any additional passengers by 2021 should a second runway be built.
“The airport will also ensure that local road networks will be no busier than they are today, even after a general increase in demand.”
The airport predicted rail capacity would double by 2020 and said it would invest in improving junction 9 on the M23 (Gatwick Airport) if the expansion was allowed.
Hugh Sumner, senior transport advisor for London Gatwick, said: “Gatwick will be road and rail ready for a second runway by 2021 with no additional cost to the taxpayer.
“Gatwick already has the highest proportion of passengers travelling by public transport and these improvements will help encourage even more.
“We want 60 per cent of our customers to use public transport, comparable with the best globally and better than any UK airport.”