London transport bosses dismissed fears of a strike on the underground train network during this summer's Olympics saying they were confident a deal could be struck that would avoid chaos for commuters and sports fans.

Transport for London (TfL), which runs most of the city's transport system, also played down talk of a potential perfect traffic storm during the Games.

However, transport bosses are still in dispute with three boroughs who object to restrictions on the Olympic Route Network (ORN), something organisers must implement to ferry officials, the media and others between venues and hotels.

TfL was also criticised for the potential impact the ORN might have on air quality during a London Assembly hearing.

Transport is a major concern for organisers, having to deal with narrow streets that are typically clogged with traffic and a creaking underground system overcrowded during peak times.

Organisers are desperate to avoid the stigma that has dogged the 1996 Atlanta Games after some athletes failed to arrive for their events on time because of transport woes.

Last week, members of the RMT rail union who work on the London Underground, known as the tube, were offered a bonus of 850 pounds each to work during the Games, the latest offer in a long-running dispute.

RMT had rejected previous offers, saying too many strings were attached, and had formally declared a dispute with London Underground, one move short of calling a ballot. But union bosses said they would consider the latest offer.

Deals have already been struck with workers on the overground, rail network and the key Olympic artery the Docklands Light Railway.

Discussions with the RMT are ongoing, the TfL's Director of Games Transport Mark Evers told the London Assembly.

We are confident that we will have a deal in place with them ... well ahead of the Games.

The objections by three boroughs to parts of the 109-mile ORN could trigger a judicial review.

The boroughs, in response to an official consultation, argue the ORN could cause congestion for businesses and restrict residents.

Host cities have to agree to an ORN as part of its contract with the International Olympic Committee (IOC).

The whole timing of the consultations have been recognising that a judicial review could take place, said Richard George, director of transport for the London Olympic organising committee (LOCOG).

TfL's Evers said some issues had been resolved, and discussions were continuing.

There are still a small number of outstanding issues which we keep working with them on, and we are confident they will be sorted in the very near future, he added.

London Assembly members also raised concerns that the ORN could adversely affect air quality because of congestion.

You know already we've had 15 bad air days in London this year, assembly member Jenny Jones said.

We are only allowed 35, and we are going to exceed them and we could exceed them before the Games.

I am just concerned there has not been enough really creative thinking about traffic reduction for the Games.

(Reporting by Avril Ormsby; Editing by Steve Addison)