The line was made single track in the late 1960s as a cost saving measure
Commuters are being urged to back a bid to back plans for a second rail track between Kemble, Gloucestershire and Swindon, to improve the route.
Gloucestershire County Council said it would boost the county's economy, and wants passengers to sign a petition.
First Great Western and Network Rail are backing the campaign saying it needs to be developed to cater for expected future demand.
The Office of Rail Regulation will make a decision in October.
Commuters can back the plans by signing the petition online.
Councillor Julie Girling said: "Without the extra track there is a real danger that the growth in new housing will far outstrip new jobs leading to a slowdown in the local economy, more people commuting out of the area and the inevitable knock-on effect of more congestion."
The track from Kemble to Swindon is part of the Stroud Valley line that has a key strategic role in linking Gloucestershire and surrounding counties with London and the South East.
It branches from the Birmingham to Bristol main line south of Gloucester, and joins the Great Western Railway route from South Wales to London at Swindon.
In a statement Network Rail back the improvement plan.
"The route suffers from regular delays and cancellations to passenger services as a result of the limitations of the infrastructure," it said.
"At peak times it operates at full capacity, but the infrastructure is unable to support an hourly timetable.
"We believe that the Swindon-Kemble project offers good value for money and would meet the objectives of improving both performance and capacity."