The first two departmental websites have moved their corporate and policy information to gov.uk, as the government's Digital by Default agenda gathers pace.
The move comes one month after the launch of gov.uk, which has replaced the Directgov and Business Link services as part of a strategy devised in part by digital champion Martha Lane Fox to transform public services online.
The home pages of the Department for Transport, the Department for Communities and Local Government, the Driving Standards Agency, the Building Regulations Advisory Committee and the Planning Inspectorate are now all available on gov.uk.
By March 2013, the single domain will host the information for 24 government departments and a number of agencies and non-departmental public bodies. This is to be followed by all remaining agencies and non-departmental public bodies by March 2014.
Last month, Cabinet Office Minister Francis Maude claimed that gov.uk will cost taxpayers up to £70m less per year than the services it replaces, but the government stopped short of the £70m mark, stating that gov.uk is "expected to save the taxpayer at least £50m annually".
In a statement, Maude said that gov.uk was designed to meet the needs of users and what they wanted to do.
"Last month, we launched gov.uk and now we are pushing ahead with moving departmental corporate and policy information on to the single domain," he added.
Cabinet secretary Sir Jeremy Heywood said that presenting policy information in one place would help the Civil Service to become more open in the way it works, as set out in the Civil Service Reform Plan.
He added that it would "become much easier for civil servants to understand the wider context when they are developing and implementing policy and for the public to access the information they need".