More than 20 trains have had to be removed from service on Northern Ireland railways as a result of graffiti.
In addition, 75 windows and windscreens have been smashed by vandals.
When added to general vandalism in train stations in 2018 to date, both commuters and Translink will be left with a total bill estimated at over £250,000.
The figures were disclosed after a Freedom of Information request.
Translink said train vandalism could be broken down into three main areas - graffiti or 'tagging' the outside of a train or coach, broken windows and the general vandalism of property at stations.
Since the beginning of January, 21 cases have been recorded of vehicles being 'tagged' that resulted in them having been removed from service for cleaning or, in some cases, repainted.
This year so far it has cost about £8,000 in direct labour and materials. However, Translink added: "This does not take account of the pressure it puts on the service to the public if a train is not available to run because it is removed for repairs.
"There have been 75 windows or windscreens broken on trains so far in 2018 with an estimated cost in excess of £150,000 for repair, and general property vandalism at train stations costs Translink around £100,000 per year.
"These costs are based on materials and labour costs but do not include the resources impacted by taking staff off other work to carry out repairs or loss of train services whilst the train is out of service."
Alliance South Antrim MLA John Blair voiced concern at the consequences of vandalism.
"I met recently with local and regional Translink managers and I know Translink will be investing heavily in new rolling stock to improve the network and the service provided to commuters and other travellers," he said.
"This will need protected and we don't want to see vital funds diverted away from improving the service provided towards these completely unnecessary and unavoidable repairs.
"Not only is it of a financial concern for Translink, it's a concern for people who use the train network every day.
"No-one wants to see money wasted in this way through needless acts of vandalism."
Translink said vandalism was a bigger problem than graffiti, and is very difficult to police.
It added: "It is reasonably predictable that the peak number of breakages occur during school holidays so we schedule store deliveries of spare glass to coincide with these holidays."
Translink warned that anyone intent on causing damage to trains or stations should be aware of CCTV cameras in operation across the network.
It added: "The cameras monitor inappropriate behaviour and, in an effort to keep everyone safe, we prosecute anyone caught damaging property or endangering others.
"Whilst it is difficult to provide quantitative evidence, we can say - at least anecdotally - that CCTV does help to deter anti-social behaviour and similar incidents. CCTV proves useful in identifying and apprehending perpetrators, assisting with police investigations or aiding prosecutions."
Translink said all issues are logged internally and work is then either contracted out or completed by small in-house teams. It explained that resources are impacted either directly or by taking staff off other work to carry out repairs, and said it causes a real problem.
The transport operator said a reward scheme is running for anyone giving evidence on vandalism that leads to a conviction.
It said community engagement is a key part of their battle to combat vandalism. "We work with community and youth groups to tackle anti-social behaviour and run education programmes on the dangers of trespassing on the railways," it added.
"By working together we can prevent potentially dangerous incidents of trespass, vandalism and dangerous behaviour on trains, near railway tracks or on station platforms. What might seem to be a bit of harmless fun or simple carelessness can quickly turn into a very dangerous situation.
"We encourage everyone to play a part in staying safe by reporting any incidents of trespass, vandalism or assault against staff members."