A rail provider has claimed it "learnt lessons" from the timetable chaos last year which led to a record fine.
Govia Thameslink Railway (GTR) promised its summer timetable will provide 2,000 extra seats to the Cambridge to Brighton service and increase its weekend services.
The launch of the changes last year led to the cancellation of up to 470 trains a day.
GTR was fined £5m by the Office of Rail and Road (ORR) over the chaos.
The new timetable will come in from 20 May and will see half-hourly services between Cambridgeshire and Sussex, via Hitchin, Stevenage and Gatwick.
GTR chief operating officer Steve White said passengers should be "confident" about the new services.
He said: "The industry has learnt many lessons from the May timetable of last year and that is evident by the way we smoothly introduced our winter timetable.
"Our passengers should be reassured the summer timetable has been planned in exactly the same way as the successful launch of our winter timetable, and the changes are rather more modest in nature."
As well as the changes to scheduling, GTR has announced a £15m fund for stations that were most-affected by the disruptions.
Mr White said the company had also paid out an additional £17m in compensation in a scheme agreed with the Department for Transport.
Passenger group Transport Focus said rail users want a smooth set of changes.
Chief executive Anthony Smith said: "They paid a hefty price a year ago for a poorly managed set of major timetable changes.
"To regain the confidence of passengers, the rail industry must pull out all the stops to ensure these improvements deliver more punctual and reliable services."
Source: BBC