BT is promising that most businesses and homes in Hertfordshire and Buckhinghamshire will have fibre broadband by the end of March 2016, following an £18.1 million deal with the two county councils to install the infrastructure.
It says it will make a minimum speed of 2Mbps available to more than 90% of premises in the two counties, with 14,000 in Herts and 38,500 in Bucks getting speeds up to 80Mbps.
BT is coming up with £8.6 million for the projects, while Herts is providing £1.6 million and Bucks £3.7 million. A further £4.2 million is coming from the Government's Broadband Delivery UK fund.
The company and the councils are going to identify which areas will be upgraded, with the first fibre cables due to be in place in mid-2014.
The leaders of both councils spoke of the deal boosting their local economies. "Superfast broadband has the potential to transform our economy and our lives as dramatically as the railways did for the Victorians," said Bucks leader Martin Tett.
BT is running a £2.5bn programme to extend fibre broadband around the UK through its Openreach local network business.