Plans to build a new £250m bypass through a country park in Merseyside are to face a legal challenge.
Highways England (HE) wants to build the road through Rimrose Valley in Litherland to ease congestion to the Port of Liverpool.
Sefton Council accused HE of failing to consult on a tunnel option and has been granted a High Court judicial review.
HE said it was "disappointed" at the ruling but campaigners say it is vital that local people "get a proper say".
Campaigners said a road tunnel should be considered to ease traffic on the congested A5036 instead of routing traffic through "valuable" green space.
But HE said a tunnel would cost £1.5bn and was not a "viable option".
Sefton Council's leader Ian Maher criticised HE's failure to consult on the tunnel option.
'On the cheap'
Cllr Maher said: "They completely disregarded this approach and ploughed on with a flawed consultation which is why we had no alternative but to apply for a judicial review."
Stuart Bennett, 40, of the Friends of Rimrose Valley said: "We feel it's all been done on the cheap.
"Rimrose Valley is valuable countryside for local residents and building a bypass would have health implications with petrol fumes and hundreds of kids having to cross it every day.
"Now at least local people will get a proper say."
HE said the bypass would improve access to the existing port as well as the £300m deep water container terminal Liverpool2 at Seaforth.
A spokesperson said: "We are obviously disappointed that this issue will now proceed to the High Court, not least because of the inevitable delay this will mean in delivering this vital investment in the Port of Liverpool route and the benefits we believe it will deliver for people in the area as well as the local and regional economy."