The Baird government wants to rip up the existing north-south cycleway on College Street and replace it with a new path down Castlereagh Street.

The government is now expected to announce a six-month cycleway trial in Castlereagh Street from 6am-10am and 3pm-8pm.

This is to allow vehicles to access loading zones outside those times.

The proposal would mean that with the loss of the College Street cycleway, there would be no full-time north-south cycleway through the southern end of the Sydney CBD.

Numerous elements of this plan, which the government has not yet confirmed, remain unclear.

The government had wanted to build the new cycleways before it started construction of a light rail line down George Street in April.

It is running out of time to do that. This means there is a chance the new cycleways may not be built for years.

It is also unclear whether the "part-time" cycleway would have a permanent barrier from the road traffic, as is the case with some cycleways in Sydney, or if it is to be marked with paint on the roadway.

An organisation called Save Our Street, headed by conservative activist Jai Martinkovits, has been campaigning against the proposed Castlereagh Street cycleway.

A spokesman for Transport for NSW said on Wednesday that a project team was examining feedback to an earlier design for a permanent Castlereagh Street cycleway and "this may include some changes to the design".

Asked if Roads Minister Duncan Gay, who has described himself as "the biggest bike lane sceptic in the government", had been pushing for changes to the Castlereagh Street cycleway, a spokeswoman for the minister said in an email on Thursday afternoon: "Any announcement will be made in due course."

Mr Gay has previously insisted he had been told by his department that Sydney's existing bike paths were in the wrong spot.

However, hundreds of pages of documents prepared by the state's roads department have said the cycleways make little or no impact on the city's general traffic congestion.

Mr Gay's office would not return calls on Thursday afternoon.