There wasn't any. I read this with a laugh. Might have been a couple of cameras on top on the road, certainly nothing underneath. Never saw the story in the local rag - Mum and Dad probably stopped us reading such things in those days.
As one grew who lived on Northcote Point near the Gold Hole* for a few years and can remember the day in 1959 as a just 5 year old when the bridge opened. As young teens we used to play around the northern end of the bridge all the time.
And when the Nippon Clippons were being fitted, we used to go up the vertical caged ladder from the Point onto the under roadway walkway. It was often left unlocked. No problems to us kids on a weekend, 175' up above the water under the main arch not a safety belt in sight. Hell, we used to build huts 70' up pines trees in the bush just to give mum heart failure from her kitchen view. Only problem was that you couldn't get off the bridge at Westhaven, some security sod had a locked gate at that end with barbed wire.
And another one for the young would be hoons of today. In Little Shoal Bay (left of the bridge, heading north) where the motel sits now was the gasworks and adjacent a tip. Yes, under those nice playing fields is a stinking great tip leaching into your fine Jafa harbour. Only in those days it was a tip which flooded with every high tide. A small one, Ngataringa Bay in Devonport was big, along with the granddaddy Auckland City Meola Road tip where the Motat planes now sit.
I assembled many a bicycle out of Little Shoal Bay tip. And my first motorbike (offroader, local bush tracks only). We used to get 3 or 4 kapok matresses and a wire-wove base tied together and launch them as rafts into the harbour. Days later, the bottom mattress would eventually get sodden, so we got a dry new one from the tip on top every so often. Herne Bay, Watchman's Island, Pt Chev reef - no probs.
Now corrugated iron and apple boxes (remember them?) were in bountiful supply at the tip. Apple boxes were good for carts with a few pram wheels. But the corrugated iron was even better. Fold it in half longways, slap in the ends of an apple box, a few nails, plug up the holes with clay, make a paddle and you had 15' canoe. Fantastic, went right round Rangitoto one day with my brother. The great expedition. Used to regularly row up and down the harbour wharves, into and out of Westhaven and around the bridge piles. Right up to Paremoremo (before the prison was built) mudflats sometimes. Not a life jacket in sight. Yes we could swim very well in those days.
I could just see the look on kids face today if they saw such carrying on making their own entertainment. Didn't cost a cent. And no doubt getting arrested for ignoring every aspect of maritime safety. Fun was plentiful and cheap in the Sixties. Fond memories.
* The Gold Hole was a big hole where the steep road went down to the boat yard at the side of the Point just down from the local boozer, the Northcote Trough in Queen/Princes St. Must have been a dig out for a temporary bridge pillar during the original bridge construction, but was long rumoured to have had gold found there.