This is not simply a numbers game, and it seems likely that your real question is whether this is a tried and proven system, in cities with similar characteristics to those of Wellington. There are a number of examples currently in operation one dating back 120 years. See our LINKS page. The best example of a location with similar terrain and narrow streets is in Japan, the Shonan Railway, which has been in operation now for 50+ years.  It takes 14 minutes to travel 6.6 km, with eight stops.

More recent (since 1988) is the Chiba Urban Flyer. Its Line 2 travels 12 km, with 13 stations, taking a total of 20 minutes.

• [It is on this basis that we estimate that the 10.3 km between Wellington Central Railway Station and the airport, with perhaps 13 stops, could be travelled in less than 20 minutes]

The oldest Suspension Monorail still running is in Wuppertal, Germany, in operation since March 1901 (120+ years), and covering a length of 13.3 km, with 20 stations, in just 30 minutes from end to end. 

It has a colourful past, because a publicity stunt in 1950 led to Tuffi, a 4-year-old elephant, jumping from an overhead carriage into the river below. She survived, and the authorities established rules preventing such foolishness thereafter.

The only fatal accident in its more than a century of operation was in 1999, as a result of a maintenance error. After the subsequent inquiry, it became a rule to perform a test run after maintenance to ensure the system was back to a safe state, and this SM continues in operation to the present.

A rather attractive but smaller system is in operation at a German university called Dortmund. Although smaller, this is worth a look because of the excellent design of its stations, with very good weather protection that would be attractive in Wellington city.

And, hot off the presses, China is forging ahead developing and expanding SM technology, having already two lines in operation (2016 & 2020, click pictures below for detail).