I recently came across this series of old videos of the Harbour Bridge, one from shortly after it’s opening and one from during the construction of the clip-ons.
It’s interesting that even back when the bridge opened, detailed counts of traffic were being taken. It would be interesting to know if that data still exists, of if it’s been lost to the mists of time. But I do have some high-level numbers. The graph below shows the average annual daily traffic volumes over the bridge from 1961 onwards. As of 2017, around 172,000 vehicles per day cross the bridge and of course many more people are crossing thanks to the Northern Busway.
One thing I also heard recently is that in some ways we’re lucky we were able to add the clip-ons. The bridge was originally designed to be five or six lanes but to save money, it was scaled back to four lanes. Apparently, the designers working on the bridge simply didn’t have time to change the design of the foundations to match the new structure and so they were built as is. But those stronger foundations were what made the clip-ons possible.
The clip-ons plus more recently the Northern Busway have helped delay the need for another, very expensive, road-based crossing, possibly indefinitely and with the way Auckland is developing, the next crossing is likely to be a PT only crossing (or PT + active if we build a bridge).