|The new Petone Interchange|
The response from NZTA is interesting, and seems to imply that they're treating Petone-Grenada and SH58 upgrading as an either/or. It's not. As one writer to the Hutt News points out this week in their letter section, the optimistic completion date for the Petone-Grenada link road is (now that the start date has been pushed back to 2015) 2024. Transmission Gully will be completed by 2020. This means the Hutt Valley will miss out on having a proper link to this vital road for four years.
SH58 is a dangerous road. NZTA implicitly accepts this fact by acknowledging that it needs "safety upgrades". These safety upgrades consist of more cheese-cutter barriers and adding roundabouts along the way. The upgrades don't address the subsidence on the road south of Mt Cecil, and won't make the road capable of carrying the extra traffic off Transmission Gully. The smart thing for NZTA to do would be to do a proper upgrade of SH58 now: a grade separated interchange at Manor Park, and straightening of the Mt Cecil section of the road.