National Rail says it will warn people if stations or trains are busy, to help them follow social distancing rules.
A warning triangle will appear on its app and website to warn customers buying tickets that a train service is expected to be busy.
It will also warn people who have signed up for travel alerts if a railway station is busy.
National Rail said it would use journey planning trends and live updates from railway staff to run the system.
Overcrowding has been an issue on some trains during the coronavirus pandemic.
The RMT transport union has threatened to halve services to protect staff and passengers.
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National Rail’s new system was developed by tech start-up Zipabout.
Passengers will be able to sign up for alerts on Facebook Messenger ... Read even more