Tim Williams used a recent presentation at Sydney University to argue the city needed a "public transport revolution" and that "all sides" of politics had got it wrong on transport planning.

The criticism was powerful and unusual because of Mr Williams' position as head of an organisation that represents firms that might expect to benefit from the construction of new motorways, and particularly the $15 billion WestConnex project.

But in a note to members this week, as well as in a letter to the Herald, Dr Williams backed away from the criticism, saying it reflected only his personal views.

"Some members will be aware that during an unscripted speech I recently gave at Sydney University I uncharacteristically commented from a personal perspective and went beyond the formal position of the Committee without clarifying I was doing so," Dr Williams wrote in a note.

"I have apologised to all partners and to my board who have been very magnanimous although concerned for 'normal service to be resumed'," he wrote.

"I also apologise to members for this untypical event."

Dr Williams' swift backdown on the presentation - which he supported with 95 slides - underlines the sensitivities around the WestConnex project, which at 33 kilometres is the largest motorway proposal in the country.

In his presentation Dr Williams was particularly critical of the failure of motorway proponents to release detailed information justifying their projects. He also criticised the chief executive of the WestConnex Delivery Authority, Dennis Cliche, for comments by Mr Cliche dismissing the concerns of people opposed to WestConnex.

The Committee for Sydney's membership includes major engineering and construction firms such as Lend Lease, Arup, AECOM, as well as financial services organisation. A number of government agencies, such as property arm UrbanGrowth NSW, the Department of Planning and Infrastructure, and Destination NSW are also members.

The chair of the Committee is the former Lord Mayor of Sydney, Lucy Turnbull.

In Mr Williams' note this week, Ms Turnbull says: 'We will always be a platform for both collaboration and challenge to ensure Sydney gets the policies it needs. But we do this without controversy and on the basis of evidence and that will always be our approach."