Edited to add Linton Bridge proposal See base of blog..
The original story.
The Manawatu Gorge is an enigma in nature. It has a river with it's watershed on the East side, and exits to the west through the gorge. The history can be found Here . As can be seen in the article, the Manawatu Gorge Road (what would become State Highway 3) was completed in 1872, days long before the advent of motor vehicles. Essentially it was built as a coach road, and probably a single lane road. It remained essentially a one lane road (1 and 1/2 really) until the 80's to 90's when extensive widening and bridging made it a tight but manageable two way road. It's fair to say, when done the road was built to a capacity of motor vehicles over to a certain standard, which in modern terms is far greater usage.
And what about that commerce. 40 years ago, the only trucks you saw in the Gorge were Stock trucks transporting livestock from southern Hawkes Bay and Northern Wairarapa to the Longburn Freezing works near Palmerston North, with smaller cartage trucks supplying the same areas. Nowadays large transport Carriers and Milk Trucks flood the Gorge daily as they go about their commerce. The reason is two fold in essence. 1. The use of trains to the East Coast has diminished and most cartage is now done by road. 2. Palmerston North is a huge warehouse hub now and supplying many areas is the norm, all done by truck and trailer. But they too share the Gorge.
The two arterial routes used by Gorge Traffic when the Gorge is closed are substandard and would also feature highly on a risk register. So what can be done to eliminate that risk? Well there are two solutions. The first is to make the Saddle Road a more viable option. Economically cheaper than the other option, but one that adds cost to motorists and commercial vehicles as the hill climbs would raise fuel bills. That leaves, to me, the only real option. A tunnel or two as it happens.
The Tararua side of the gorge, topographically, is more generous to a road link and safer than the Gorge. Cutting two short tunnels, both four lane affairs, and making a road between them another four lane effort, would free up time and money to all travelers, and support organisations that maintain the current roading network through the gorge and the two arterials (Saddle and Pahiatua Track) It would increase productivity to both sides of the divide as well. It would also cut down travelling time and fuel/vehicle costs. So here it is. The Rangitaane Tunnel (Manawatu side) and the Kahungungu Tunnel (East Coast side). Of course a new bridge over the Manawatu River would have to be built on the East side where the Kahungungu Tunnell exits..
Ok crazy idea, but if they can build countless motorways in Auckland and Wellington to cater for increased traffic volumes (bugger public transport) they can ease a risk area in an important part of the highway network in this area.
Editted on 10 April 2015 to add new photo as previous data seen in previous tunnel proposal rendition was flawed due to topography issues in Google Maps. This new one has just one tunnel as there is no dipping plateau between the entry range and exit range.
Added 22 October 2017 with proposal/thoughts about a one lane bridge from Linton Army Camp to Rongotea Line, thereby bypassing going though the heavy traffic of the city.
The first image shows a rough depiction of the road. Details are:
New sealed road from Linton Camp to the Manawatu River.
A One Lane wide standard construction bridge.
Sealed road from bridge to Rongotea Line.
Culvert Bridge with Linton Road going under the existing Pioneer/Longburn Road.
This image shows closer detail of the bridges and roading.
This shows that it should be relatively cheap (read inexpensive) to set up a very much needed crossing for Army Transport to have quicker access from Linton to Ohakea and onto Waiouru.
The bypass cuts out city traffic and gives a very much needed secondary crossing in case the Fitzherbert Bridge is out of action through natural disaster and Civil Defense and Armed Services still have a crossing. At this stage it should be a private road/bridge for Service use only.
It's probably going to save Army vehicles in slow traffic areas in city traffic a bit in fuel and maybe around 20 minutes on the road.
A Win/Win for all[.