A 1.1% average increase in the cost of train tickets in England, Wales and Scotland has come into effect.
The rise in regulated fares, including season tickets, is capped at no more than July's RPI inflation rate of 1%. This is the smallest rise in six years.
Unregulated fares, such as off-peak leisure tickets, can go up by as much as train companies like.
Under government rules, the rise in regulated fares was restricted to no more than the Retail Prices Index measure of inflation over the year to July, which was 1%.
The increases, which were announced in December, cover fares in England, Scotland and Wales. Northern Ireland is treated separately.
Commuters with annual season tickets can find out how much their fare has gone up by on the National Rail Enquiries website.