→Average road speed "shrinking window": rephrasing for readability
==Average road speed "shrinking window"==
is enough recorded speeds on a road, then Waze uses a shrinking window of speeds to better estimate the average speed at the time you are travelling on it. Waze uses the speed of each road segment in intervals as small as 30 minutes , for each direction. So a two-way road may have up to 48 average road speeds. We can assume that when there is insufficient records for an individual time slot, a wider time range is taken, up to the full day. As the road is driven more, the time slot would shrink down to 30 minutes.
We can speculate that there may be additional information used
by the day of week. There is some observational evidence that a road that is busy on weekdays and not used for routing , will be chosen as the optimal route on weekends.
At some point Waze would also need to consider the months of the year as seasonal variations can affect the speed of the roads.
Waze uses the average road segment speed for the time slot that applies at time you are expected to arrive at
a road segment.
Because of this "time window", Waze will suggest different routes at different times of day.
But it is dependent on how many times are recorded on the roads along the route. And if they're all recorded at about the same time of day, then the time window will not help. If 1000 times are recorded at about 5pm and 2 times are recorded at 10am, then your 10am average speed will still mostly be based on times from around 5pm.
==Routing algorithm refinements==