The cost of the Croxley Rail Link has soared to almost £150m after years of government indecision and battles against red tape.
However, the on-again off-again saga appears back on track after the scheme was this week backed to receive a £120m investment.
The rail link, which will extend the Metropolitan Line into Watford Junction, was priced at £66m in 2006.
Just one year later, the scheme is now estimated to cost close to £150m, if completed by 2014.
The rail scheme will, however, only be given the go-ahead if £119.5m is invested by the Department for Transport (DfT).
This week, the project received a huge boost after it was backed by a transport panel at the East of England Regional Assembly (EERA) on Tuesday.
The regional assembly has rated the scheme as a “priority” in its list of transport policies.
Furthermore, it has now recommended the government contributes the £119.5m towards the costs.
Hertfordshire County Council has already guaranteed the remaining £25.8m for the rail link.
The news means that after years of battling through red tape and against several public departments at once the rail link’s business case will again be sent to the Department for Transport, where the project will be decided.
Mayor of Watford, Dorothy Thornhill, said the process was now about getting “all our ducks lined up in a row”.
She said: “What this means is the East of England Regional Assembly sees this as an important project.
“If it didn't say that then central government would not take it seriously.
“It is a small milestone and we just welcome every little milestone that gets us nearer.”
She added she has written to Mayor of London, Boris Johnson, to get Transport for London to back the scheme.