Question: Why is it some days traffic on the freeway is very slow and other days it moves well in the same locations? 

Answer:  That's a question with a lot of possible answers!  Today (Columbus Day) I drove from Santa Clara County to Oakland.  The drive usually takes about 1 hour 15 minutes in the morning peak.  Today it was less than an hour.  Traffic was a little lighter than usual because a few folks get Columbus Day off but the big difference was on northbound I-880 between I-238 and I-980.  The Port of Oakland must have been closed for the holiday because there were no container trucks on this portion.  Usually slow-and-go, today the drive moved at 55 mph or faster all the way into downtown. 

Container trucks make up about 10% of the usual traffic volumes, and removing this small percent of traffic can yield big benefits.