An example is AP's pre Qld election announcement of $2 billion for road widening and other treats where the Gateway Mwy meets the Bruce Hwy. The "we're gonna do it" announcement was reinterpreted at the time by the bureaucracy as
planning, with the aim of
The business case gets you a place in the infrastructure priority list
The design and construction process of course involves option selection and evaluation and more consultation through the EIS process. Add anotjer year or two for that before you get to calling for tenders!
As soon as it gets contentious you can expect years to morph into decades, the classic example being the replacement, then second, Sydney airport.
cheers skip