Calderdale Council wants to introduce a bus lane on the A629 Elland bypass approaching the Ainley Top roundabout and the M62.
The road is the major route between Halifax and Huddersfield and in the rush hour buses get caught in jams that can add 20 minutes to journey times.
The plan is one of a series of proposals, costing more than £350,000, to help speed up public transport.
But motorists today said the idea would cause chaos.
Sarah Carroll, 23, a technical adviser for Marshalls, Halifax. said: "I travel to and from Elland every day and if the bus lane is introduced it will cause difficulties."
Driving instructor, Andrew Rawnsley, 40, said: "I have a problem teaching on dual carriageways because the road is congested. Plans for a bus lane would be better if the lanes were widened. The idea will just create chaos."
Shawn Bartholomew, 38, a fitter for Quality Conveyors, of Queensbury, said: "Everyone in the company uses the road and the fact that there don't appear to be many buses makes it even worse. There is obviously no real need for it but to upset motorists."
Garth Corbridge, 55, a joiner from Halifax, said: "I hate using the road at the best of time and this will make it worse."
Kieran Douglas, 38, an electrician from Holywell Green said: "If I know I am on a morning job I will avoid the road and go through Ripponden, even if it means an extra two miles."
The plan follows council talks with transport operators to try to ease the problem and stem the decline in bus use.
A study has shown that without the measures, an extra 300 cars a day could soon be driving along the A629 into Halifax causing added congestion and parking problems.
As well as turning the inside lane on the Elland by-pass into a bus lane on the approach to Ainley Top, other proposals include:
l Extending to evenings as well as mornings the use of the Skircoat Road bus lane between Free School Lane and the Arriva Ford Garage.
l Widening Stainland Road to create a new bus lane up to the Calder and Hebble junction.
l Introducing bus-controlled traffic signals at West Vale.
l Moving a key stop in West Vale to the Halifax side of the village and improving access to Heath Road, Halifax.
Part of the A629 bus lane beside the Shay stadium was scrapped last year after claims that it caused vehicles to queue back into town. There are no plans to reinstate it.
Council regeneration director Janet Waggott said studies showed that without intervention there would be a significant decline in bus use by older people who have grown up in an era of unrestricted car use.
She said: "Congestion can lead to some buses running 10 or 20 minutes late while others have to waste time at stops at quiet times to have a consistent timetable.
"Such uncertainty of timing is often quoted by people as a reason not to travel by bus."
About 3,200 bus users travel the A629 every day and the number is expected to fall to 2,900 within five years and to 2,600 in 10 years.
"This could result in up to 300 and 600 extra vehicles that would need to be accommodated on the A629 and in town-centre car parks and on-street parking."
Geoffrey Wainwright, a council representative on West Yorkshire Passenger Transport Authority, said a bus lane at Ainley Top would not only speed up bus journeys but by turning three carriageways into two, make it safer for general traffic.
"Buses lose a lot of time on the way to Huddersfield, particularly in the morning and the changes shouldn't seriously disadvantage other drivers," said Coun Wainwright (Con, Skircoat).