How to identify road classification

They probably do a very strict correlation called "RANDOM" :D

In the U.S., interstates are always multilane (at least 2 lanes per direction), divided and have limited access. They should correspond to fastest/highest quality roads in a country. Major highways in the U.S. probably refer to our older U.S. highway system. These roads may or may be divided and may or may not be multilane. However they are designed to be traveled at a faster speed than other roads (no sharp turns), but the maximum speed is less than that of an interstate in a given state (there may be some exceptions where they are equal, but never higher).

Other Highways are usually our state highway system and perhaps some county roads. These are usually not divided, have 1 lane per direction and will pass thru nearly every town in their path. Speeds may vary, but they will always be less than an interstate. Collector roads are probably best described as the major thoroughfares within cities. Residential Roads are everything else.

On the Garmin U.S. maps, Interstates and some U.S. highways are colored orange with interstates being the superior roads (Interstates and Major Highways?). Some U.S. highways and some State Highways are colored yellow (Other Highways?). Some state roads, all county roads and all other roads are white. Hope this helps.

If you like to think in total numbers, there are fewer Interstates than U.S. Highways (Major Highways), which are fewer than Other Highways.

As a side note, changes to the speed settings aid in planning from the sense of arrival and departure times, but in my experience, they are not used when the application determines an initial route. I assume the default values are always used in for identifying the initial route. This would make sense as at least some devices do not allow you to set these parameters.

And yes, they really should publish a road classification cross index.

Thanks for that, very helpful!

This touches on a problem I have when I use the "Profile" parameters to calculate my route drive times. I get the idea that the actual road designation (state-xx in a round circle) is the driving factor for determining average speed. And I can see how you might think a state highway, for example, would have an average speed of, say, 60 mph. But what about when that state highway consists of nothing but twisty, windy, roads -- like CA-1 (in BaseCamp named Big Sur Coast Highway), and you know you're not going to get over 45 mph avg? Do I somehow have to have the knowledge of the terrain so that I can use the BaseCamp Route Options->Speed->Customize function to adjust the speeds over the selected Route? Because that's what I think Garmin is suggesting. And I guess you have to have an inherent knowledge of the road conditions on routes that travel mountains or foothills. Seems that BaseCamp is going to haul ass through those terrains at a high rate of speed. Maybe this isn't a problem for most users. I however am doing this on a motorcycle, and it's critical to know how long it will take to drive a particular route.

If you need to tweak route highway speeds, it will require users to break out sections of the route, so that their speed limits can be modified separately.

Where can I find definitions of Profile speed adjustments for functions labeled "Curvy Roads" under Customized Route Options; Road Preferences?

Where can I find definitions of Profile speed adjustments for functions labeled "Curvy Roads" under Customized Route Options; Road Preferences?

Dane2 -
Curvy Road route planning on BaseCamp is not quite perfected yet (but on Zumo GPS directly it is pretty good right now): https://forums.garmin.com/showthread.php?191282-Curvy-Road-routing-logic-in-BC-4-4-6