The US Court of Appeals for the District of Columbia Circuit has reinstated the environmental approval, a prerequisite for the $US 875m Transportation Infrastructure Finance Innovation Act loan allocated to the project by the Department of Transportation.

The state says construction could begin within weeks of receiving a commitment to federal funding.

However, with president Donald Trump’s opposition to federal funding for transit construction, it is unclear whether the ruling provides a strong enough basis for the Department of Transportation to commit to releasing funds.