Folks, I went to DOT and got what they call an SLD (single line drawing) map set. This basically compiles data on the highways in a linear format -- the data point of current interest is speed limits, of course.

Thanks to everyone's help, we've made a decent start on Oahu, but these maps will help with neighbor islands. It's still tedious, of course, but at least you get a hint of where to look on Street View to confirm a speed-limit change.

I thought I'd share the download link from my Google Drive here, in case anyone's interested. I'm slogging through Kauai -- or I will be, after work today!

The document files:

How to use this document:

Oahu

Kauai

Hawaii

Maui