What is the logic behind the "Street Level Routing" Travel Estimations?

Summary:

We'd like to better understand how Oracle/Google determine which is the correct Travel Estimation to use when SLR is invoked, as we're not convinced that the travel times being returned are the optimal ones.

For example, when i check on Google Maps for a route between 2 addresses i get these 3 options returned:

The Travel Time applied by SLR was 55 Minutes, which Google suggests is the shortest possible time it could take to make the trip at the time of day the Resource was planned to travel. The shortest, but ultimately completely unlikely to achieve. Google even suggests that the Resource wouldn't arrive till "about 11:00" which suggests they use the longer side of the estimate, no the shorter one. Surely SLR should be following similar logic, using either the longer estimate or some kind of calculated middle ground.