A MAXIMUM cap of $7.35 in tolls will be put on the West Connex when it opens, with a minimum charge of travelling on the road to cost $1.50.

The state government will release its planned tolls for the road today at a briefing of construction experts at Bicentennial Park.

Driving the widened M4 from Church St, Parramatta to Homebush Bay Drive will cost $3.90 when it opens in 2017, with a minimum charge for one small section of $1.50.

The M4 East section from Homebush Bay Drive to the City West Link, to open in 2019, will cost a maximum of $3.60, with a minimum leg of $2 and an average cost of $2.40.

The M5 East Airport link from Beverly Hills to open in 2020 will cost a maximum of $4.80 and a minimum of $1.70.

The M4 South between Haberfield and St Peters, to be finished in 2023, will cost a maximum of $4.10 with a minimum leg of $1.80.

But, just like the M7, there will be a cap figure of $7.35 to ensure the tolls do not become so uneconomic that drivers dodge the motorway.

All the figures are in 2013 prices so will rise by an average inflation rate of about 3 per cent a year by the time the motorway opens.

Premier Barry O'Farrell and Prime Minister Tony Abbott have announced funding of $1.8 billion and $1.5 billion respectively for the 33km, $11.5 billion project.

The government says it will lead to 52 sets of traffic lights being bypassed, 40 minutes travel saving on a typical trip from Parramatta to Sydney Airport and 3000 trucks a day taken off Parramatta Rd.

The business case for the project shows it will cut the travel time from the CBD to Parramatta from 50 minutes to 25 minutes. The government is not ruling out providing more public funds for the project should the tolling not cover the remaining cost.

Announcing the project last month in The Daily Telegraph, Mr O'Farrell described it as a "game-changer for Sydney" which would " save motorists time''.