The British Transport Police (BTP) data shows that 1,448 offences were reported in 2016-17, up from 650 in 2012-2013.
The data revealed to the BBC covers England, Scotland and Wales and includes the London Underground. It indicates that the majority of the incidents recorded were sexual assaults on females aged 13 and above.
"Tackling all forms of unwanted sexual behaviour on public transport is a priority for British Transport Police and we have worked hard in recent years to send a clear message to victims that they will be taken seriously and we will investigate offences," said BTP's Detective Chief Inspector Darren Malpas.
The force believes that the hike in figures shows an expected rise following BTP's "Report it to stop it" campaign.
Rachel Krys, co-director of the 'End Violence Against Women Coalition', praised the effort BTP and train companies have put into campaigns to encourage victims to report abuse.
Krys highlighted research conducted on London's Underground network, referred to as the Tube, that showed that a majority of offences took place during rush hour in tightly packed trains, rather than as a result of heavy drinking.
"It is really important that these campaigns continue. When the scale of sexual violence is better understood, police forces take it more seriously and measures can be taken to reduce the risks to women and tackle perpetrators, who for too long had been acting with impunity," she said.
"Research on the London Underground last year showed that the majority of these offences happen during rush hour, dispelling the myth that this is anything to do with a late- night drinking culture.
"These figures showed that it is sober men, travelling to and from work who thought they were entitled to assault women passengers, and that they would get away with it," Krys said.