Pre-tax profit for the six months to 30 September was £17.7m compared with £8.7m for the same period last year. Turnover rose 27% to £443.3m.
Jarvis' share price has more than tripled in the last year to 500p after falling to 168p last November amid City criticism of its management and business strategy. Its has outperformed most competitors, including Amey and Interserve, over the last year.
Analysts said Jarvis' mix of long-term transport contracts and PFI meant earnings were guaranteed, making it an attractive investment.
One analyst said: "Jarvis has turned itself around after the hits a few years ago and is in some good markets. It has won some lucrative contracts, such as the Tube deal."
Chief executive Paris Moayedi said: "We continue to benefit from our focus on specialist markets which provide clear, non-cyclical long-term demand, and which have high entry barriers."
He added that the group was well placed to win more long-term rail and road work.
Moayedi said Railtrack's collapse had had little impact on its rail work, which includes contracts on the east and west coast mainlines. He said the government would continue to modernise the network.
The operating profit of the group's rail division more than doubled from £5.1m to £11.3m; turnover rose 57% to £206.5m compared with the same period last year.
The group announced that it had set up two joint ventures. The first, Jarvis Primary Health, is in the healthcare, IT and multimedia markets. It will provide primary care outsourcing. Jarvis' partner is venture capital company Sinclair Montrose, which has transferred 12 properties to the venture. It will be headed by former Jarvis director Henry Lafferty, who left the firm in August.
The second joint venture, Agilisys, will target business processing and IT outsourcing in the public sector. It has been set up with IT firm Netdecisions.