The rail tracks run along the road at the crossing site
Concerns have been raised about the long-term safety of a new narrow gauge railway crossing in Gwynedd.
Bike wheels have gone into the tracks at Porthmadog, and there were a number of accidents at the Britannia Bridge before they were temporarily filled in.
When the Caernarfon to Porthmadog Welsh Highland Railway line opens in 2011 they will need to be reopened.
The train company said when properly completed the crossing would be made safe for all road and rail users.
E-mails and letters concerning the crossing at Britannia Bridge were made public under a Freedom of Information Act request.
One shows that in April last year the then chief constable of North Wales Police, Richard Brunstrom, was seriously concerned about the situation.
In an e-mail to Chief Supt Geraint Anwyl, Mr Brunstrom said "this crossing is patently unsafe for cyclists".
He added that although there is a sign telling cyclists to dismount to cross the line on foot , "at present it is a death waiting to happen".
Broken collar bone
Following the e-mail from Mr Brunstrom, Chief Supt Geraint Anwyl wrote to the Welsh Highland Railway about the crossing.
He said there had been a "number of collisions at this location where cyclists have been thrown from their bikes as a result of wheels dropping into the railway line".
He said one of the cyclists had a broken collar bone while others had minor injuries.
The "risk to road users at this location is wholly unacceptable, and I would most strongly urge you to implement an engineering solution in order to alleviate the problem," the letter said.
There are signs at the site asking cyclists to dismount
He also said the railway company had been warned on several occasions, it had "duty of care to road users," and there was a possible breach of that duty of care.
"In such circumstances, if a fatal collision occurs at this location involving a pedal cyclist, I will as commanding officer initiate a robust investigation into 'corporate manslaughter'.
When the railway line is open all the way in 2011 the tracks will need to be accessible to up to six trains a day.
Local councillor Selwyn Griffiths said there had been concerns about the safety of people travelling or walking across the bridge from the beginning, and there had been meetings with the railway company and police.
Cyclist Tommy Collins, who lives in Porthmadog and rides hundreds of miles a week, said the crossing was dangerous, especially for people who are unfamiliar with the layout.
"Luckily I'm quite an experienced cyclist... and I think I'm safe, but with weather conditions as they are anyone could fall," he said.
"Visitors and kids might not understand it's dangerous for them," he added.
In a statement the company said the tracks across the Britannia Bridge had been in place since June 2008.
There were also bilingual signs warning road users of railway tracks in the road, and advising cyclists to dismount and walk across.
"Until the crossing design is finalised and approved the company has covered the rails with tarmac enabling traffic to flow in exactly the same way it did prior to the installation of the track," the company said.
"The completed crossing will make full provision for pedestrians, cyclists and road traffic to interact safely with railway traffic.
"Cyclists will be diverted via a clearly marked route which takes them safely over the rails," it added.
North Wales Police said the situation was being carefully monitored.