The Campaign for Better Transport (CBT) has warned that slashing the transport budget could result in fewer buses, a rise in rail fares and more potholes.
The CBT's report showed that fares could increase by 33% if they rose every year by the rate of RPI inflation plus 3% .
Rail transport could suffer even further as a lack of extra carriages could lead to overcrowding on trains.
Cutting the Government's bus service operator grant would result in 7% fewer services, a 6.5% fares increase and 94 million fewer miles of supported services.
The CBT also warned that it is vital to properly maintain the roads.
CBT executive director Stephen Joseph said: "Our research shows that on transport spending the Government has a choice.
"It can go for easy cuts, taking money out of all budgets, upping fares and giving priority to big roads. Or it can go for smarter cuts which protect the spending that helps the economy, meets carbon and environmental targets and strengthens communities."
Mr Joseph added that roadbuilding projects were poor value for money and maintaining, and making better use of, existing roads should be the priority.
© Press Association 2010