Speed limits have been tightened on the high-speed rail line between Amsterdam and Breda after track operator ProRail said defects in the design of five viaducts could have a greater impact than first thought.

The decision to cut the maximum speed from 120 kph to 80 kph was taken after “new conclusions” were drawn from an investigation into 10 viaducts along the route.

The design flaws first came to light two and a half years ago when ProRail discovered that the structure was too lightweight to cope with the strain of trains travelling at up to 300 kph, causing cracks to appear.

Dutch national train operator NS branded the decision unacceptable and said passengers faced longer journeys and missed connections as a result.

NS International, Eurostar and Belgian train operator NMBS also run services on the high-speed line.

In February NS cut the service on the line from five trains an hour to four after fewer upgraded Intercity trains were delivered than originally planned.

ProRail said it regretted the decision to reduce the speed limit, but safety had to take priority. “It may be necessary for us to run fewer trains to ensure that the service remains reliable,” a spokesman said.