I've that a zone has to be at most three tiles away from a road for it to develop.

In addition to that, I think I've read somewhere that there's some maximum distance a Sim is willing to drive from any residential tile to any industrial/commercial tile. So industrial and commercial zones that are too far away will never get developed. Rails, highways, and subways would increase a Sim's driving range.

So, does anyone know what a Sim's maximum drive distance is?