Why aren’t there traffic jams everywhere all the time?

"There are twenty houses on my block, and each house has an average of 2-1/2 cars.  That’s 50 cars.  Why isn’t there a perpetual traffic jam on my block?"

The answer is simple: staggered usage.  We have different schedules, and we’re out on the streets at different times of the day.  Some of us make fewer trips a day than others, and some don’t drive at all.  The greater likelihood is that there might be only one car in motion on our block at any given time, with long intervals of no usage in between.

These principles lie at the heart of traffic engineering analytics.  They explain why our streets have the capacity to handle additional traffic load comfortably.