Variables Navigation uses to estimate arrival time

[taxjoc]

My wife and I took a long trip in our 2016 X5 last week. We used the navigation system to guide us and give us the estimated time of arrival. The system is great because it will add time if there is an accident, road construction, etc. that will delay the trip. That is nice and I understand it. However, I wonder what variables the system uses to evaluate the estimated time of arrival. In my prior vehicle, its navigation system allowed you to adjust the average speed on a given type of road (e.g. interstate, county road, etc.) so that it could more precisely estimate the time of arrival. The X5 does not have such an adjustment. So, what variables does it consider? Is there any literature on this? I am sure the system considers the type of road and your speed over the past few miles or so. Any one have any more information on this?

[double_j]

Given that I've seen my navigation ETA be wrong by as much as 20-30 minutes (mostly underestimates time) I'm guessing that it uses too few or too many variables.