Dublin Corporation's director of traffic, Mr Owen Keegan, and the director of the Dublin Transportation Office (DTO), Mr John Henry, reject criticism of the QBC from motoring interest groups.
"You can't solve the traffic problems of any city by using cars. You have to look at other solutions," Mr Henry said.
The Garda, Dun Laoghaire/Rathdown County Council and Dublin Bus also expressed support for the introduction of a number of QBCs throughout the city.
Dublin Bus intends to increase the number of inward-bound buses from 52 to 72 in the three hours from 7 a.m. every morning, a promise of a bus every 2 1/2 minutes on the corridor to cater for an additional 1,800 passengers. The bus company says this is a "great leap forward" in terms of public transport.
Some 25 extra gardai are to be deployed to ensure compliance with the new rules, and Dun Laoghaire-Rathdown County Council has lent its "wholehearted support".
Mr Keegan says having through-ticketing, real-time information displays at bus stops and park-and-ride facilities would mean starting with a "gold-plated" service, but he insists that "substantial improvements in service" mean it would not be reasonable to delay the introduction of the QBC.
Existing bus customers have made a choice which is in line with public policy, and they should be rewarded for it, he adds.
But in relation to those customers who do not live within walking distance of the QBC and who cannot readily avail themselves of it either through lack of park-and-ride or feeder bus and transfer facilities, he said: "We are not looking for every motorist to transfer on day one.
"We cannot continue to cater for the private car. The capacity is not there. Of course, there will be some adverse impact on general flow but we didn't set out to impact on general traffic," he said. He added that in any policy there would be winners and losers.
While there were clearly possibilities for improvement, he admitted, the QBC should not be "held off until we have everything in place. We have capacity and frequency.
"Our version is that we will open with substantial improvements. We are not seeking every driver." Indeed he points out that the bus service will not be taking all of the road and he returns to the argument that the other improvements mentioned by the AA will come.
In a later phase it might be possible to build the park-and-ride facilities, he said, but these would come to spread the catchment area of the bus corridor.
"At the moment if only the motorists within walking distance of the QBC used it there would be a significant enhancement of capacity in the route."
A spokesman for Dun Laoghaire-Rathdown County Council said the issue of QBCs had been adopted as policy by the council for many years.
The council was particularly pleased that the morning rush hour QBC route would not, as originally intended, travel through Stillorgan village but via the bypass, stopping at the subway to allow passengers access to the village.
The council also pointed out that it was intended to extend the bus priority route to Dun Laoghaire port as well as to Bray, Co Wicklow, in the future.
Meanwhile, Dublin Bus said that improvements in the bus fleet over the last 10 years meant that many commuters transferring back to public transport would find it a surprisingly pleasant and financially rewarding change. Almost 800 new buses have been bought in the last nine years.
The Stillorgan corridor will be followed by others in Blanchardstown and Finglas, while early next year it is planned to introduce QBCs in Rathfarnham, Clondalkin, Tallaght and Swords. In all 11 QBCs are planned for the city and suburbs.
