The woman, 26, was filmed cycling through the barrier at Waterbeach in Cambridgeshire on 12 September.
Following an appeal by British Transport Police (BTP), she came forward voluntarily, officers said.
At the time of the incident, rail bosses described it as "one of the closest near misses we've seen".
BTP released the CCTV of the Cambridge woman passing the closed barrier and ignoring warning signals and lights.
Hundreds of thousands of people watched the footage of her cycling up to the tracks before slamming on her brakes, and edging backwards as the train sped past.
Moments later the woman was seen mopping her brow before cycling off in the direction she had come from.
Her actions forced the driver of the train to apply the emergency brake when he saw her, operator Greater Anglia said.
More than 100 trains travel through the Waterbeach crossing each day, at speeds of up to 75mph (120km/h).
Since 1 January, there have been 70 reported incidents at level crossings in Cambridgeshire, a BTP spokesman said.
However, incidents such as this one were "extremely rare", he added.
The woman was cautioned under section 36 of the Malicious Damages Act 1861.
The section covers incidents of "obstructing engines or carriages on railways", which carries a maximum sentence of two years in jail.

The vessel has been called the world's best example of a 15th Century ship by archaeologists.
And new evidence has found that the timbers from the ship have been matched to projects built in the Basque region.
It includes new data from medieval buildings in the Araba and Navarra areas of Spain.
"The mystery of the origins of the Newport Ship, the remains of the a remarkably well-preserved medieval ship may at last have been solved," said Nigel Nayling, associate professor at University of Wales Trinity Saint David.
"Artefacts found at the time of the discovery hinted at Iberian connections but recent advances in dendrochronology (tree-ring dating) have provided the first scientific evidence.
"The results strongly suggest that the ship was originally built in the Basque Country where wooden shipbuilding has a long tradition.
'Useful insight'
"A Basque origin for the ship has been suspected for some time and collaboration between the scientists was first suggested in 2006 by Xabier Agote, president of the Albaola Society which promotes research into Basque maritime heritage."
Mr Nayling said initial attempts to date the ship were unsuccessful.
But he added the latest results have come from research programmes sampling both the ship itself and more historic buildings that have allowed extension and improvement of the medieval section of the Basque chronology.
Debbie Wilcox, cabinet member for leisure and culture at Newport City Council said: "The ship provides an excellent opportunity to tell the story of medieval Newport and its history as an international maritime town long before its development as an industrial port.
"The latest information about the Newport Ship provides a useful insight into its origins and it appears that one of the mysteries of its history may have been solved."
Newport council has put a tender out to developers asking them to recommend a suitable location for the vessel.
It is seeking a specialist company who would be able to provide a new museum based around the ship's history.
A cyclist who dodged a closed level crossing barrier, coming within inches of being hit by a train, has been formally cautioned by police.
[NEXT_CONCEPT]
A medieval ship discovered on the banks of the River Usk in Newport in 2002 may have come from the Basque country in Spain.