Most bridges and viaducts in the Netherlands date from the 1960s and 1970s. They were designed for the traffic of that time. On some routes, eight times as many vehicles now cross them, and a fully loaded lorry weighs around four times what the designers allowed for.
Concrete and steel wear differently
Engineers also calculated differently back then. In concrete bridges from that period, shear force was often underestimated. That is the force that tries to cut straight through a structure. Under today's calculation methods, bridges like these are more likely to fail the check. Yet measurements show time and again that there is more load-bearing capacity in the structure than the old sums suggest.
Rijkswaterstaat, the government agency that looks after the national roads and waterways, manages 1,149 bridges. The most recent overview of the state of the infrastructure lists 72 bridges, viaducts and tunnels under intensified inspection, because of age, technical risks or deferred maintenance. And those bridges are not all concrete. The Merwedebrug, the Haringvlietbrug and the Van Brienenoordbrug are on that list as well. All three are steel.
A steel bridge rarely gives way under a single heavy lorry. It is the repetition that counts. Hundreds of thousands of crossings make the steel flex by a fraction each time, and tiny cracks appear in the welds that grow a little further with every lorry that follows. Engineers call this fatigue.
The bill keeps growing
For the period 2026 to 2030, Rijkswaterstaat puts the renewal of bridges, tunnels and locks at almost 12.9 billion euros. More than 6.5 billion of that is not yet funded. So the challenge is far bigger than whichever bridge happens to be closed today.
And central government looks after only a small share. Municipalities alone are responsible for 66,000 of them, and more than 80% of all bridges, locks and viaducts belong to regional and local authorities. Dutch research institute TNO has calculated that renewing Dutch infrastructure up to 2100 will cost some 260 billion euros, and that 55% of that will land with municipalities.
Age tells you little
That estimate rests mainly on age. Age gives an indication of when a bridge is due for replacement, but on its own it says too little. "A fairly young bridge can be due for replacement because its technical condition is poor, while an old bridge can last much longer because its load-bearing capacity is still sufficient", says Andreas Hartmann, associate professor of infrastructure management at the UT.
The real problem is that municipalities in particular have no clear picture of the actual condition of their bridges. Between them they manage tens of thousands, far too many to have each one recalculated the way Rijkswaterstaat does. "It is a matter of gaining better insight into the behaviour of existing bridges through closer inspection and monitoring", says Andreas.
Measuring beats guessing
That insight often works out well. Take the Maaslandse Dambrug in Schipluiden, the only road into an outlying part of the municipality of Midden-Delfland. On paper, no more than 20 tonnes were allowed across it. Engineers then put a test load of 450 kilonewtons on it, three-quarters of what the standard prescribes including all safety margins. The bridge barely moved and can last at least another 30 years. Load tests in Leidschendam, Waddinxveen, Den Bosch and Amsterdam found the same thing every time.
So how bad is it really?
For Rijkswaterstaat, the answer is reasonably hard. Those 1,149 bridges are closely watched and close as soon as an inspection finds something, as at Nijkerk. For the tens of thousands of municipal bridges, the answer is an estimate based on the year of construction, and that keeps turning out to be a poor predictor.
Dutch bridges are probably in better shape than the replacement figures suggest, and less well understood than you would want. Every bridge that does get measured turns an assumption into a fact. Those 30 extra years for the Maaslandse Dambrug mean it does not need replacing for now. And that means more money can go to a bridge that does.
