Bus and train operator Go-Ahead posted a 13% drop in half year pre-tax profit and remains cautious about the wider economic outlook.Pre-tax profit fell to £44m in the six months ended 31 December from £50.7m the year before. Revenue for the period rose 5% to £1.2m. Go-Ahead reiterated that it remains in a good financial position with strong cash generation and a robust balance sheet. It also saw robust trading in bus and rail, in line with management expectations."Looking ahead, whilst we remain suitably cautious about the wider economic outlook, in rail we expect first half revenue growth trends to continue in the second half and in bus we expect a solid performance despite an impact from the implementation of a new contract," it said in a company statement."Overall, we continue to anticipate the group will deliver full year results in line with management expectations."Go-Ahead has maintained its interim dividend at 25.5p.