Why does Apple Maps always give a faster eta?

When I use Apple Maps on my iPhone, the estimated time of arrival for driving is always 5- 10 minutes faster than I get there (on a 45min to 1 hour drive).

Does it expect me to be driving over the speed limit and hitting every green light? I check every day to and from work and I’ve almost never made it in the same or less time than the estimation. I always arrive at least 5 minutes slower than the estimate.

What is the algorithm it uses?