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Residents of a dress circle of high-value homes in Manukau City's southeastern sector are among hundreds being notified of a major arterial road corridor potentially heading through or close to their properties.
The city council has narrowed a route - for its approximately $100 million share of a four-lane road of about 14km between Drury and Flat Bush - to three main options, even though construction is probably at least 10 years away.
Although the council hopes no more than "about a dozen" homes will have to be removed, it expects it will need parts of up to 70 properties, and to have to realign the driveways of a further 100 or so.
Papakura District Council has yet to announce options for its section of about 10km of the new arterial route, which would skirt its town centre before joining the Southern Motorway at Drury.
It could cost at least as much as the Manukau one.
But Manukau has decided to open public consultations in time to select a route and begin property purchases next year, ahead of population booms in Flat Bush and Takanini - to around 40,000 people each.
Information open days will be held on Saturday and Tuesday next week to unveil detailed plans to about 400 property owners sent notification letters.
Much of the route will be along the existing two-lane Mill Rd, which the council believes is already becoming overloaded by about 10,000 vehicles a day.
That is expected to rise to about 25,000 vehicles once the road is upgraded along what the Auckland Regional Transport Authority lists as one of the region's top-12 new arterial corridors for priority treatment.
But Manukau is considering two potential deviations as alternatives to the existing road's full alignment, as well as a major upgrade to the busy intersection of Redoubt and Murphy Rds, on the ridge between Flat Bush and Totara Heights. The largest deviation, of about 2.1km, would include about 400m of Redoubt Rd east of its intersection with Mill Rd and then a new alignment to the south which would hook back into the existing route between Polo Prince Drive and Ranfurly Rd, on the Manukau-Papakura boundary.
Alternatively, a smaller 800m section of Mill Rd could be moved east - away from Polo Prince Drive - to limit disruption to traffic for the years it would take to build the new arterial.
The council is also seeking public comment on whether it should build a "grade-separated" intersection or a signalised junction at the top of Totara Park, through which half the future traffic is expected to head to or from Flat Bush, and the rest to or from central Manukau.
Council transport manager Chris Freke said the route was through one of Manukau's most geologically challenging sectors, and every option presented big engineering challenges.
A land slip this month on Redoubt Rd which cut water supplies to thousands of homes, although to the east of the project's catchment, illustrated a need to be "very careful where we put a road".
He said the council had ruled out any direct route through Totara Park, given its high natural values and other property impacts, but acknowledged traffic ramps to and from a separated intersection would encroach on the top end of the park.
* Public open days: Saturday, 11am-2pm, Alfriston School. Tuesday, September 2, 4.30pm-7.30pm, Flat Bush School Hall.
