How much do rankings change from year to year in the list?
In most years, sections of road near the top of the list (top 25) tend to stay near the top of the list because congestion is intense and occurs during many hours each weekday and during some hours of the weekend. Sections outside the top 25 tend to have congestion in one direction in the weekday morning and the other direction in the evening. Road sections in the bottom half of the Top 100 may bubble in and out of the Top 100 because congestion changes on these roadways is often caused by nearby office, retail or commercial developments and road construction on the corridor itself or on a nearby parallel or intersecting facility. These traffic changes can be permanent or temporary; before solutions are considered, it is important to understand the causes.
In a COVID-19 year, the 2021 Top 100 list contains 30 sections that were not in the 2020 Top 100 list; this is up from 17 new sections from the 2019 to 2020 list. More arterial street sections were included in the Top 100 list in 2021 than in the 2020 list (33 sections in the 2021 top 100 compared with 28 in the 2020 list).