There were long tailbacks on roads around Utrecht on Wednesday morning as farmers on tractors gathered in Bilthoven to protest about the way the public health institute RIVM measures the concentrations of nitrous oxides and other pollutants.

Farmers say that they are bearing the brunt of emergency measures to combat nitrogen-based pollution and that the calculations used to measure emissions must be wrong.

Hundreds of farmers on tractors blocked rush hour traffic as they headed for a sports park near the RIVM offices, having been banned from the actual location because of safety fears. All but essential RIVM workers have also been told the stay home.

Nu ook tractoren die de snelweg blokkeren of rijbaan-breed rijden. Aan hen de oproep zo veel mogelijk rechts door te rijden zodat verkeer veilig kan passeren. Sta je stil? Stap niet uit. #veiligheidvoorop #boerenprotesten pic.twitter.com/EK1zzxwLtR

— Rijkswaterstaat Verkeersinformatie (@RWSverkeersinfo) October 16, 2019

According to some reports, as many as 3,000 farmers and 1,500 tractors may have travelled to Bilthoven for the morning demonstration.

Later on Wednesday the farmers intend to head for The Hague to hold a protest rally near parliament. On Monday the farmers held local protests targeting provincial governments.

Farmers interviewed on Radio 1 news said the RIVM must be making miscalculations.

‘The heather fields I drive past are still purple and the woods are still green.’ Micha Bouwer of action group Farmers Defence Force said. ‘And I drive through them every day.’

Another farmer said: ‘Look at the Oostvaardersplassen [nature reserve]. It is yellow with ragwort.’ RIVM workers are ‘civil servants and don’t really understand it’, he said.

In the Hague, the police have brought in army trucks to seal off key crossings and areas to stop the farmers getting to the Binnenhof parliamentary complex.

De blokkades in De Haag worden opgetrokken #Boerenactie #boerenprotest pic.twitter.com/pIIcBpYDhE

— Roel Bolsius (@rollebols) October 16, 2019