The M6 Toll road is being used by less than half the number of vehicles it was intended for as it marks its fifth birthday.
The road, which was the UK's first pay-as-you-go motorway when it opened in 2003, was intended to ease congestion on the M6 through the West Midlands.
A public inquiry in 1995 said the road needed 100,000 vehicles a day to justify its existence.
But it only attracted 43,064 on average between July and September.
This was down 12% on the figure for the same period in 2007.
Midlands Expressway Ltd, which runs the Toll, said the drop was due to the "continuing weakness in the UK economy which has seen a greater decline in discretionary (weekend) travel".
The road cost £2 to use when it opened but now charges £4.50. This is due to rise to £4.70 in 2009.
BBC Midlands Today transport correspondent Peter Plisner said this made it one of the most expensive toll roads in Europe.
Haulier Eddie Stobart has called for use of the toll road to be subsidised to ease congestion on the main M6.
Phil Spittle, the firm's general manager for fleet and compliance, said: "I believe £150m has been invested to try and ease congestion in the west Midlands.
"If a percentage of that, maybe 5% of that, was used to compensate truck users to use the toll then I think they would stop congestion on the M6 for the private user."
Tom Fanning, chief executive of Midlands Expressway Ltd, said: "Traffic levels are seasonable generally by the way of nature and as for October, November, December it tends to fall and from then onwards it goes up again."