A new road linking the M4 to Cardiff International Airport seems unlikely to be built, even though it is supported by a report commissioned by the Welsh Assembly Government.
Cardiff was the quickest-growing airport in Britain last winter
Consultants say the £37m scheme would cut traffic jams west of Cardiff.
Faber Maunsell said better public transport and junction and road improvements would help, but recommended the extra road in the long term.
But the assembly government is said to be worried about opposition, and wants alternatives to be examined.
These would include turning the existing airport route into a trunk road.
Faber Maunsell was asked by the assembly goverment to look at solutions to congestion problems on the western edge of Cardiff, leading to the Vale of Glamorgan.
Traffic at the Culverhouse Cross interchange has almost doubled in the past 10-12 years, and is expected to increase by about 35% in the next 10-15 years.
There have been complaints for years about the complicated road journey to the airport.
The new road recommended by the consultants could be built within 10 years if planning work began quickly.
It could give a further boost to the airport, which was the fastest growing in Britain last winter.
More than 600,000 people used the airport between November 2002 and last April.
The airport has been examining further improvements when road and rail links are improved.
A rail link from Cardiff to a nearby terminus in Rhoose is due to open later in the year.