Shocking CCTV shows a woman lying down on railway tracks to pose for photographs despite the dangers.
A woman in a bright jacket can be seen sprawled across the rails at a level crossing in East Sussex while her companion takes pictures.
Footage shows the pair hanging around by the tracks for around 50 seconds shortly before 11.30am on Monday.
Pictured: Two women's actions were branded 'unthinkably stupid' by British Transport Police after one lay down on a level crossing near Seaford, East Sussex, while another took a picture
The stunt at the crossing - where trains pass through at up to 70mph - has been branded 'unthinkably stupid' by police.
The incident at Tidemills level crossing near Seaford is the latest instance of dangerous behaviour on the railway which could have ended with fatal or life-changing consequences, according to Network Rail.
It is the 17th incident at this crossing in the last nine months, with 15 recorded near misses.
During the whole of 2019, there were only four recorded incidents, with three recorded near misses.
Tracy Partridge, East Sussex level crossing manager at Network Rail, said: 'We are concerned about repeated dangerous behaviour at Tidemills level crossing which follows the near misses which took place last year.
'We cannot stress enough the danger that people are placing themselves in when they don't use a crossing safely.
The picture of the procession (pictured) was released by Network Rail to remind people to be more careful at Tide Mills level crossing, near Bishopstone, between Seaford and Newhaven
'A split-second decision can have life-changing consequences, not only for those involved, but also for their family and friends, train drivers and railway workers.
'Please, never take chances when using level crossings and if you have any concerns, always contact Network Rail or British Transport Police.'
Other dangerous behaviour at Tidemills has included level crossing users filming the emergency stop of an oncoming train.
In another incident, cyclists narrowly missed a train, while large groups of pedestrians have experienced close calls by trying to beat approaching trains.
Cameras have also captured a funeral procession using the crossing.
British Transport Police Inspector Jonathan Pine said: 'This is unthinkably stupid behaviour by two women clearly oblivious to the dangers of level crossings.
The footpath crossing which takes people across the railway is regarded as the busiest pedestrian crossing in the country and has been identified as 'very high risk' (pictured)
'Trains pass through this line at speeds of up to 70mph, so they could quite easily have been moments away from a catastrophic incident.
'We've seen first-hand the consequences of this sort of recklessness and no photo opportunity is worth risking your life for.'
Local people and visitors will soon enjoy safer access across the railway at Tidemills in the South Downs National Park after Network Rail's proposals for a new footbridge were approved.
Once the new footbridge is in place, the footpath crossing will permanently close.