The number of congested hours per day are not directly comparable
across different urban areas because data collection coverage
on the freeway system in each urban area can vary dramatically. In
this case, the data cover about 65 percent of all freeway lane-miles
in Los Angeles, compared to about 22 percent in Chicago where data
collection is focused on a smaller, more congested portion of the network.
In addition, Chicago tends to have lower free-fl ow speeds on its
monitored freeway network compared to Los Angeles.