I know this topic has been done to death, but I feel it needs to be re-stated just how important it is for Waze to work offline. I went to Yosemite this weekend (go nearly every year, it's great), and every year since Waze was released, it has been completely useless once I got anywhere near the park.
The biggest issue with Yosemite is the lack of cell coverage. Only in the Valley itself is there any service, and it's typically Edge / 1x speed...not enough for Waze to operate efficiently. Many of the roads out of the valley such as Tioga road or highway 41 are either filled with traffic at one point or another, under construction, or closed due to weather / rockslides. If any roads need adequate coverage, it's those two.
Now I understand that controlling cell coverage is beyond the power of Waze, but I think we need to anticipate such conditions. Waze already caches a large portion of the route in the beginning, that's good. But it needs the whole route AND several miles (perhaps a setting that the user can specify) around the route. That way if I lose coverage halfway through Tioga pass, I'd still have maps of the entire park on hand. As it happened, despite having hours of 4g / 3g coverage on the way up, I lost all my maps halfway through Tioga pass. Not that I needed them, but not every driver has been to Yosemite as often as I have.
Another function should be to cache driving conditions, reports, road closures, etc... and mass-upload the data as soon as possible. While this may not help with immediate traffic conditions, it will help build the historical average that Waze supposedly takes into account, as well as storing GPS tracks that can help flesh out the local roads. This could be of great service when calculating whether to take highway 41 out of the big valley or highway 395 out of the Eastern Sierras (although 395 is more scenic...but I digress).
Finally, Waze should be allowed to calculate a route without requiring a network connection first...relying on the cached maps that were stored when first entering the no-service area. I found myself having to rely on my offline-saved google maps to check for points of interest such as gas stations instead of Waze.
I think the easiest thing to do would to be just have Waze cache everything it would normally send to the servers, if it lacks cell coverage at the time. Then once you reconnect to a good cell signal or WiFi at a hotel in the valley, it will upload everything that was stored. Combined with the ability to download maps for offline use, Waze would be useful anywhere in the country.