Passengers in the south are being asked for their views on a plan to improve the line from Sussex to London.
Network Rail is holding a series of consultation events, as well as encouraging people to take part in a survey online.
It is developing proposals to remove the railway bottleneck at Croydon, with new flyovers replacing junctions, and East Croydon station rebuilt with two extra platforms and better facilities for passengers.
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The move could improve reliability for the 300,000 passengers who travel on the Brighton Main Line and its branches each day, Network Rail said.
Rail services from across Sussex run through East Croydon to get to central London stations.
John Halsall, Network Rail’s managing director in the south east, said: “Removing the Croydon bottleneck is the only practical way to provide the step-change in reliability and capacity that passengers and businesses on this vital growth corridor so desperately want to see.
“We’ve had a tremendous response to the consultation over the past few weeks, with thousands of people attending events and responding online.
“With only a few weeks left until this phase of consultation closes I’d like to encourage passengers and businesses to have their say by coming to one of our events or feeding back on-line.”
Network Rail is also carrying out a major project to renew and upgrade tracks and signalling on the southern end of the Brighton Main Line. Work is taking place at weekends as well as during a nine-day blockade in February 2019.
Other ongoing improvements to the line include power supply upgrades across Sussex to allow longer and more frequent trains to run in the future and an upgrade of the old signalling system on the Lewes to Seaford line which is taking place at weekends and over a four-day blockade of all routes via Lewes, including to Haywards Heath from March 7 to 10, 2019.
Consultation events on the Croydon bottleneck plan will be held on Monday, December 10 and Tuesday, December 11 from 4pm to 8pm, at the Brighthelm Centre, North Rd, Brighton.
People can also take part online until Monday, December 17 by visiting: www.networkrail.co.uk/Croydon
Network Rail will hold a second round of consultation on more detailed proposals in summer 2019.