First, NYC has a variety of different road types, and most cities have at least some highly mixed roads. I'm not sure where NYC's cameras were positioned, and I'm at work, so I can't read up on it.

And other studies have also shown speed cameras to be effective:

Twenty eight studies measured the effect on crashes. All 28 studies found a lower number of crashes in the speed camera areas after implementation of the program. In the vicinity of camera sites, the reductions ranged from 8% to 49% for all crashes, with reductions for most studies in the 14% to 25% range. For injury crashes the decrease ranged between 8% to 50% and for crashes resulting in fatalities or serious injuries the reductions were in the range of 11% to 44%. Effects over wider areas showed reductions for all crashes ranging from 9% to 35%, with most studies reporting reductions in the 11% to to 27% range. For crashes resulting in death or serious injury reductions ranged from 17% to 58%, with most studies reporting this result in the 30% to 40% reduction range. The studies of longer duration showed that these positive trends were either maintained or improved with time.

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004607.pub4/abstract