How to Build a Decent Cycle Road Between Petone and Ngauranga

As long as I can remember (which goes back to the early 1960s) cyclists have been riding along the Western Hutt Road's stopping shoulders.
There has always been a "cycle-track" between the road and the railway, and it has always been totally useless for regular cycle commuting, mainly because of its poor geometry. Not too long ago a shipload of money was spent on this white elephant, but cyclists are still forced to ride on along the stopping shoulders, because the "cycle-track" is too dangerous.
I've ridden along the stopping shoulders myself. I've also done a fair bit of cycling in other parts of New Zealand. I've cycled so many miles that most parts of my road cycle have been worn out and replaced at least once.
This experience has taught me a thing or two about the practical requirements for a decent cycle road. What I've learned fits well with readily available cycle road design handbooks, such as the UK Department of Transport booklet, "Cycle Infrastructure Design".
The most important point is that cycle commuting is only practical if the cyclist can maintain a reasonably high speed, typically at least 25 kph for an hour, or 30 kph for a shorter commute. To do this safely, the cycle road must satisfy certain requirements, most importantly, lane width, curve radii, and visibility around curves. One of the main reasons I will not use the existing Petone to Ngauranga "cycle-track" is that it does not satisfy these requirements. Some curves are so narrow and tight that if you meet someone coming from the opposite direction you will crash. No ifs or buts. You'll go head-on into another cyclist at a combined speed of about 50-60 kph. Not pretty.
I feel safer riding on the stopping shoulder. A car driver would need to go out of their way to intentionally run you down. I've had the odd car driver swerve to the left to "buzz" me. That's scary, and I suspect they are taking out their frustration at the inadequate road system, which they wrongly blame on cyclists. Many of the people who oppose motorway expansion also promote cycling, so perhaps some young blokes think all cyclists would like to ban cars and trucks. If so, they are wrong-headed f***wits. Of all the cars I have owned, the one I would most like to get back behind the wheel of, was a V8 Valiant. Not all cyclists are anti-car. Some of us cycle for the fitness benefits.
I reckon the Western Hutt Road should incorporate a decent two-way cycle road suitable for cycle commuting. In Wellington, tailwinds can easily push you up to 35-40 kph. The cycle road must allow for this, with sweeping curves and wide lanes. Most importantly, it MUST be off-limits to pedestrians. Pedestrians on shared tracks are unpredictable, they tend to step into your path just as you pass them. I've crashed badly more than once avoiding pedestrians on shared tracks and still have the scars to prove it. I swore off shared cycle/pedestrian tracks more than ten years ago.
The absolute minimum width for a two-lane cycle road is about four metres (two metres north-bound, two south-bound). It should also include a stopping shoulder wide enough for people to stop for a breather, or to change tyres.
Adequate maintenance is vital. Only a concrete barrier separates the cycle road from the motorway, so a bottle chucked out of a passing car can land on the cycle road. It only takes one cheeky little shit to chuck a Heinie bottle out of their window to create a serious hazard on the cycle road. The Western Hutt Road is so busy that the chance of this happening, at least once a week, is pretty-much one hundred percent. That is why the cycle road should be regularly cleaned by a street-sweeping machine. This means the cycle road should be wide enough to allow a cyclist to comfortably pass the street-sweeping machine. I suspect most cyclists will be happy with a four metre road plus a one metre stopping shoulder, provided the street sweeper is no more than about 1.8 metres wide.
Another important requirement is that roading authorities should treat cycle roads as seriously as they treat other roads. Which is why I call them cycle roads, not cycle-tracks.
We can convert the existing left-hand north-bound lane of the Western Hutt Road between Ngauranga and Petone into an excellent cycle road. This would provide a two-metre wide lane in each direction, a one metre shoulder against the hill, and a 200 mm shoulder between the south-bound lane and a concrete barrier between the cycle road and the motorway.
Most of the rest of the existing road would be taken up by the three south-bound vehicle lanes. A bit of the existing stopping shoulder, and the existing "cycle-track" should be reserved for an additional railway track.
While we are at it, we might as well build a footpath along the seaward side of the railway (fenced off from the railway tracks). (As mentioned previously, the north-bound side of the motorway would run along the hillside well above the existing road.)
It's very simple to connect this cycle road into the rest of the roading system.
At Ngauranga, the ramp carrying the north-bound lanes up onto the hill-side would fly over the cycleway, which would run alongside the motorway to the intersection of Centennial Highway and the Western Hutt Road (at the bottom of the Ngauranga Gorge).
At Petone, the north-bound carriageway would cross a flyover that carries it down to ground level near Cornish Street. The cycle road would run under this flyover, emerging on the western side of the motorway, and climb up to the Korokoro bridge which carries it across the railway and onto the Main Hutt Road.
This completely separates cycle traffic and motorised traffic between Petone and Ngauranga.