A troubled rail operator has said it is "too early to say" if its third new timetable in two months is causing disruption.
Thameslink, Southern and Great Northern passengers have faced disruption since a new timetable began on 20 May.
Govia Thameslink Railway (GTR) said the latest timetable would provide a "more robust and reliable service".
On Monday it said: "Our focus is on the evening peak and rest of the week as we introduce the new interim timetable."
Monday is the first working day of the new timetable, which GTR said "provides passengers with a more robust and reliable service, gives priority to peak hour trains and seeks to reduce gaps in the service".
There has been a mixed reaction from commuters.
One St Albans Commuter said: "I just got on the 8:12. It's running on time and the train is full, but no worse than before the timetable change really."
Another said: "So far it's looking ok this morning. My fear is the return when trains aren't in the right place for the new timetable."
In Harpenden, Hertfordshire, Charlotte Halkett tweeted that "there still appear to be huge crowds & delays to trains".
Dear #Thameslink. This week was supposed to be the start of your new strong & stable (if hugely reduced) timetable. And yet there still appear to be huge crowds & delays to trains. Could you please help me out with why? Confused Of Harpenden #saveHPDtrains @TLRailUK @IanProsser7— Charlotte Halkett💃🏠 (@charliehalkett) July 16, 2018
Meanwhile, on the Royston to London Kings Cross line, Kieran Walker called the new timetable a "failure".
"Cancelations and delays everywhere today," he tweeted.
"7:38 Royston to LKX is dangerously overcrowded and now has 3 extra stops? £5k!! Disgusting, pathetic service."
@OliverHealdUK @BBC3CR @GNRailUK Timetable #3 FAILURE!! Cancelations and delays everywhere today. 7:38 Royston to LKX is dangerously overcrowded and now has 3 extra stops? £5k!! Disgusting, pathetic service. #goviaout pic.twitter.com/CoY41Ikhsj— Kieran Walker (@kieranjwalker) July 16, 2018
GTR, which oversees Thameslink, Southern and Great Northern routes, changed the time of every train on its timetable on 20 May, which saw some services withdrawn and further cancellations without any warning.
In a half-page newspaper advert, initially placed in the Metro newspaper and since then replicated in local papers, it apologised and acknowledged it "failed to launch new services as planned" which has resulted in "significant delays, cancellations and disruption".
An interim timetable introduced on 4 June to improve performance saw about 6% of daily services removed, but reliability has continued to struggle.
The operator said the changes would mean a 13% increase in services across the GTR network - 400 extra trains a day and new direct services from 80 stations into central London, creating space for 50,000 extra passengers at peak times.
Its website said the timetable would continue to evolve over time.
"Once this interim timetable is bedded in, we will look to introduce more services to complete the intended May 2018 timetable," it said.
Govia Thameslink's ongoing problems
- A series of failures have been blamed for causing the chaos, including Network Rail's late approval of the new timetables and delayed electrification projects
- Poor planning by train operators has also been blamed, and the decision by transport ministers to phase in the introduction of new GTR services
- The damaging impact of the new train timetable was demonstrated in punctuality figures published by Network Rail on Monday
- GTR chief executive Charles Horton resigned last month
Last week in the House of Commons, the government warned improvements to GTR services were "simply not happening quickly enough" and the train operator risks losing its franchise.
Standing in for Theresa May at Prime Minister's Questions on Wednesday, Cabinet Office minister and Aylesbury MP David Lidington said: "We have launched a review of Govia Thameslink which will report in the next few weeks, and if those findings show that Govia is at fault we won't hesitate to take action whether that's fines, restricting access to future franchises or stripping them of the franchise.
"Passengers deserve far better than they're getting at the moment in terms of service and we will hold those operators to account."