Published today, the foundation's paper, Public Transport Effects on Road Traffic: Potential and Limitations, says that even with significant increases in investment, switching from private to public transport remains difficult.
Making public transport cheaper by increasing fare subsidies could reduce car traffic, but several billions of pounds would be needed every year to have a measurable impact, it added.
The report questions whether the public transport network could cope with a surge in growth, because of an already congested railway network. Adding that improved local bus services would only stop a limited number of people travelling between towns in the car.
RAC Foundation director Stephen Glaister said: "Public transport is important but it will not solve our transport problems. Even if billions of pounds more than the UK is currently spending were available and spent wholly on public transport it would only have a marginal impact on getting people out of their cars.
"Motorists already pay in excess of £45bn per year in motoring taxes. Many will say that the cost of motoring is too low and that it needs to be increased to make public transport attractive. The truth is that public transport will only ever be suitable for certain trips and certain markets, and the private car will remain the dominant form of transport.
"Rather than pricing people out of the market for car use, we need to develop a whole new system for paying for motoring, which supports the development of public transport, pays attention to vehicle emissions and allows people real choice when making their journeys."