How we did it:

First, we divided the Los Angeles freeway system into nine different segments. For example, we looked at the 10 freeway from Santa Monica till it intersects with the 5 freeway near Downtown. Then we looked at another segment of the 10 between the 5, heading east till it crosses the 57.  Then, we divided each section into two directions (e.g., east and west on the 10, or north and south on the 5).

Using something called the ADMS database, we were able to calculate the average speed in each directions for every hour of 2017. We then grouped those hours into days of the week, so we have a reading for all Mondays at 6 am, all Tuesdays at 6 am, and so forth. Then, we calculated the average morning and evening rush hour speeds on each section in each direction. Morning rush hour is 7-9 am; evening rush hour is 4-7 pm. Finally, we ranked them from fastest to slowest, and we also looked at the fastest and slowest day of the week.

Still have questions about our process? Write to us at askus@crosstowntraffic.org