The West Midlands business community has called on the Government to speed up trials of a £100 million series of congestion-busting measures on the M42.
It believes the Highways Agency's projected results deadline of 2008 for Active Traffic Management - which includes variable lane speed limits and hard shoulder running - is "unacceptable" and that an assessment of the system should be available by the end of next year.
Jerry Blackett, chairman of the the West Midlands Business Transport Group, said until the results of the M42 pilot scheme around the NEC and Birmingham International Airport were known, the HA was unable to make a long term recommendation to the Department of Transport "concerning the capacity solutions for the heavily used piece of motorway".
In the letter to Transport Secretary Alistair Darling, Mr Blackett said: "It is critical that we learn the lessons of active traffic management as soon as possible.
"We are very uncomfortable with the ATM pilot not producing results before the end of 2008.
"Accepting the requirement for seasonal variations to be understood, it seems to us that at least 80 per cent of the learning from this pilot will have been gathered within 12 months and that a reasonable assessment can therefore be made by the end of 2006.
"This assumes the date for switching on the hard shoulder running element can also be advanced".
Mr Blackett, who is also policy director for the Birmingham Chamber of Commerce, said the region was "putting enormous efforts" into expanding the airport and the NEC, both of which depend on motorway access.
"HA forecasts from two years ago indicated that increasing the capacity of this motorway would be inevitable.
"While the present active traffic management system may make some contribution in the coming years to reducing congestion on this stretch of the motorway, it remains very difficult indeed to see how this can be a long term enduring solution."
ATM is in place between junction 3a, its links with the M40, and junction 7, the M6 link, on the M42. Last month, the HA introduced mandatory variable speed limits on the road and in early 2007 plans to start using the hard shoulder as an extra lane for cars, when congestion levels are particularly bad.
A HA spokesman said: "It is very important to the success of the ATM project that individual stages of the scheme are properly evaluated.
"Recently, we introduced new variable mandatory speed limits to the M42 to help motorists in the region and it is important that we assess how successful these have been before implementing the next stage of the project, which is hard shoulder running.
"Evaluation of this sort takes between six and 12 months due to the seasonal nature of traffic flows on this stretch of motorway. We are planning to introduce hard shoulder running in early 2007 so meaningful results should be available by 2008."