Train and bus operator Go-Ahead expects to post a full-year profit ahead of expectations as high petrol prices and tough economic conditions prompt drivers to abandon their cars in favour of public transport.Outgoing chief executive Keith Ludeman said the company has seen solid growth since the depths of the recession in 2008. "Three things are driving growth - improving levels of quality, better marketing of our services, and the higher costs of motoring resulting in the public choosing the better value option of the bus," he said.The de-regulated bus division, which operates in cities such as Oxford and Brighton, is expected to post full-year like-for-like revenue growth of 4%. The regulated London business is expected to see a 2% reduction. In rail, the Southern franchise is expected to see like-for-like passenger revenue climb by 9%, with Southeastern posting growth of 9% and London Midland's coming in at 8%.Ludeman will be replaced at the helm of Go-Ahead by David Brown next month."Whilst we are encouraged by our performance this year, we remain suitably cautious on the medium term wider economic outlook," Go-Ahead says.---RG