Avondale-Southdown Rail Corridor Full Map

Here is a full map of the corridor route. It is derived from the map in the Wikipedia article.

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The map in the original article will update whenever Trainweb’s server gets around to updating its cache (or may be dependent on your ISP’s caching as well).
Knowing the route a bit more precisely lets me write some sort of route description which is as follows. All the descriptions assume the railway is at the surface at the points referenced.

• From Avondale the line turns to cross New North Road then running through open reserve/parkland to reach a small bridge. Average gradient: 1 in 200
• Continuing to Richardson Road the average gradient has steepened to 1 in 50.
• From there to Sandringham Road the gradient eases to average 1 in 150.
• Gradient is then more or less flat, or can easily be made to be, until reaching Hillsborough Road when it drops at a very steep 1 in 35 to Queenstown Road.
• There is then a more or less flat stretch until Quadrant Road.
• From Quadrant Road the line drops at 1 in 50 to Onehunga Mall.
• After that it averages 1 in 60 down to Victoria Street.
• It eases to about 1 in 80 down to Captain Springs Road.
• It is then more or less flat to Neilson Road.
• From Neilson Road to Westfield it drops at average 1 in 180.

Conclusion is that there would be a substantial amount of gradients averaging 1 in 50, unless it is possible to lower the summit. Since a substantial part of the route is at the summit altitude, or similar to it, this would be very expensive. Probably the best use of earthworks is to average the climb as much as possible so that the steepest 1 in 35 part can get eased out. The total route length would be around 13 km. 1 in 50 grade is simply not seen on newly constructed main lines today for any significant distances. Most of this grade is over the eastward 7 km. The average gradient is around 1 in 100 but in truth it is two climbs separated by a flatter section.