The court has allowed Dr Emma Tristram to go ahead with a juidicial review of the government agency’s selection of its preferred route for a bypass, which would run from Crossbush Junction and reconnect with the A27 north of Walberton.
According to Leigh Day, the law firm representing Dr Tristram, her case has been prompted by concerns about the scheme's possible impact on the local environment.
It said the court decided that the case raises arguable questions of law in relation to Highways England's consultation on the potential route.
Leigh Day solicitor Tessa Gregory said: "We are pleased that the court has granted permission and we will now prepare to argue our client’s case at the High Court over this decision which she believes is unlawful.
"Proper regard must be given to the potential damage to the National Park and Ancient Woodland, and all consultees should be apprised of the true extent of environmental damage that will be caused by the current preferred route."
Highways England announced the route as its preferred option on 11 May, despite concluding that it would have a "very large adverse impact" on biodiversity and a "large adverse impact" on the landscape.
Dr Tristram’s case claims that information in the consultation brochure was misleading; expressions of support by the public for the route was based on out-of-date traffic figures; and the public was not given the opportunity to consider revised traffic figures.
In addition, the consultation also contained numerous material errors and omissions which "cumulatively, gave a positively misleading impression of the impact of the preferred option on Binsted village, Binsted Woods and historic Binsted Park", Leigh Day said.
The High Court granted permission for judicial review on all grounds, the firm said.
According to Leigh Day, Dr Tristram is crowd funding her legal challenge through website CrowdJustice, which shows £13,270 had been raised at the time of publication.
Highways England was asked for a comment but had not responded at the time of publication.
West Sussex County Council selected the same route for the bypass in October 2017 despite recognising that the scheme would have a "significant impact on the South Downs National Park and its setting".