$120 million per km of cycleway!

Back in August 2018 (just 18 months ago) the cycle and pedestrian bridge known as SkyPath was costed at $67 million for the three km cycleway. That is $23 million per km.

In January 2020 the Government has announced that it will cost $360 million, or $120 million per km.

How can something increase 440% in 18 months?

How can a cycleway (even one over a harbour) cost $120 million per km?