Legal action is being taken against a construction firm over the spiralling costs of repairing the guided busway in Cambridgeshire.
The busway, which links St Ives to Cambridge, opened in 2011 after delays and financial rows.
Constructor BAM Nuttall's costs rose from the £87m agreed with the council, to more than £150m.
However, faced with a further £36m bill for repairs the council said it would be taking action against the company.
In 2013 Cambridgeshire County Council took the company to court over the cost of the busway, but the dispute was settled in October 2014.
However, a council report identified £36.5m of repairs to the concrete tracks on the guided sections of the route and further legal action is now planned.
"The county council has agreed to proceed with legal action against BAM Nuttall in respect of defects in the design and construction of the guided busway," it said in a statement.
"Our legal and technical advisers are preparing the county council's formal claim, which will be a public document, so it would be inappropriate to comment in advance of that."
Campaign group Smarter Cambridge Transport claims it would be better the scrap the busway altogether rather than spend millions to repair the concrete tracks on the guided sections of the route.
Members have suggested replacing it with a Tarmac track or light railway.
The group is asking the council to "conduct an open re-evaluation of the busway, independently of any action it takes against BAM Nuttall".
A spokesperson for BAM Nuttall said the company did not wish to comment at this time.