The company's comments come just a week after its sister company, Dublin Bus, revealed that its vehicles now travelled at walking pace during rush hour.

Transport sources have also indicated that revenue growth at the company during 2006 was less than expected due to a combination of congestion and increased competition from private operators.

A spokeswoman for Bus Eireann refused to comment on precise impact that private operators were having on the company but she said that the company was very concerned about congestion.

"It's a huge problem facing us in terms of trying to grow our business and encouraging people to use public transport, " she said.

"The problem is that the implementation of bus lanes is a matter for local authorities and while some are very progressive, others less so."

She said that the company was experiencing particular problems in Limerick, which still has no bus priority measures, although there had been significant improvements in Cork, where a series of bus lanes known as 'green routes' have been launched.

She said that the 'green routes' had demonstrated that people would switch to public transport if it was quicker and as reliable as their own cars.

"It shows that buses and bus lanes are a winning formula, " she said.