THE trilling of spokes, cyclists rounding the bend in unison: no, this is not the Tour de France. It is the new underground bicycle park at Utrecht Central railway station, which opened last year. Three storeys deep, with electronic monitors indicating where spaces are available, it has room to park 7,500 bicycles. “It’s a bit of a maze,” says Xander Staal, who takes a picture of his bike’s berth as an aide-memoire each morning before commuting to Amsterdam.

The Netherlands is experiencing an underground bike-park boom, as cities race each other to build the largest. The Hague had hoped to overtake Utrecht this spring with a new park with 8,500 places, but that has been delayed by construction problems. Later this year Utrecht’s park will expand to 12,500 slots, surpassing a 9,400-space one in Tokyo to become the largest in the world. Amsterdam is playing catch-up: a 4,000-space garage is to be built next to its central station in what is now the river IJ. Railway stations will need over 140,000 more spots by 2030, many underground.

The Dutch are already the world’s cycling champions, with an estimated 1.3 bicycles per person. Yet pedal-powered travel is still growing, especially in combination with trains, says Wim Bot of the powerful cyclists’ union. The proportion of trips to railway stations made by bike (rather than foot, bus or car) has risen from 36% in 2005 to 45% today.

That threatens to turn the space around stations into a sea of aluminium. Police are removing illegally parked bikes faster. Spots underground in Utrecht are free for 24 hours to draw commuters in, but €1.25 per day after that to prevent them being used for storage.

Yet even as private bicycles move underground, new invaders are clogging Dutch pavements. The country now has at least nine commercial bike-sharing schemes, which often allow users to leave their wheels anywhere once they are done with them. Last year Amsterdam announced it would remove any share-bikes dumped outside designated zones. Meanwhile, the national government’s latest cycling plan, released last month, envisions spending €250m to the end of 2022 on new paths and parks. The aim is to lure 200,000 motorists to switch to cycling, and to increase annual bike travel by 3bn bicycle-kilometres in 2027. Time to dig some more garages.