The Warringah Freeway (nee Expressway) is the gigantic, 16-lanes-wide freeway north of High Street - you can't miss it. The bridge which carried trams from North Sydney onto the bridge was demolished to provide enough room for the freeway to link into Bradfield Highway.
The Cahill Expressway itself does not sit on top of a former tram route - SHB lanes 7 & 8 do.
I can't say I agree with this. The tram bridge crossed the six lanes of highway leading up from the low point between Falcon Street and the Harbour Bridge. That is, next to Milsons Point Station, or 50 metres or so north of it. Those six lanes have the elevated bridge structures on both sides. The Milsons Point Station on top on the west side, and the elevated structure on which the Cahill Expressway toll gates operated until this year, on the other. Those two concrete structures are basically original since 1932 and the width between them hasn't changed.
Now it may be the case that the number of lanes at this point was increased from 4 or 5 lanes to six lanes, by making the lanes narrower. But the width of the space between those concrete structures hasnt changed. But there is no reason why that tram bridge would have been removed for the purpose of connecting the Harbour bridge roadway to the Warringah Expressway, because the tram bridge was not obstructing the 6 lanes at that point, and the connection between the bridge roadway and the Warringah Expressway is several hundred metres north of there.
It is also my understanding that the Cahill Expressway is not just the road over the top of Circular Quay Railway station. The Cahill Expressway starts near High Street North Sydney and includes the roadway which is lanes 7 and 8 of the Harbour Bridge ( which replaced the tram tracks ), and then continues over Circular Quay to Wooloomooloo or wherever. It is my understanding that lanes 1-6 of the bridge are the "Bradfield Highway" and lanes 7 and 8 are the "Cahill Expressway".
So I think the statement that the Cahill Expressway sits on top of the former tram route, would appear to be right.
The Cahill Expressway was finished in about 1959. I don't know if it was all finished at the same time. Approaching from the north, the structure forming the ramp which leads up to the Cahill Expressway tollgates was build about that time, and although the concrete mouldings were made to match the existing pattern, the slight difference in structure can be seen from Milsons Point Station.
That ramp up to the Cahill Expressway tollgates was built for the Cahill Expressway around 1959 and wasn't later altered for the Warringah Freeway, except for the approach to it at the northern end, which is also a visibly different batch of concrete where they didnt bother to match the 1930's decorative pattern.
The Warringah Freeway was not opened until about 1971.
The tram bridge was removed because of the 1959 alteration ( introduction of the Cahill Expressway ), not the 1971 introduction of the Warringah Expressway.