Overall, about 20 percent of the monitored miles of limited-access highways experience travel congestion (LOS F) during the peak travel periods. Since this is based on travel speeds averaged over the peak periods, it is likely that additional highway segments also experience congestion at some point during the peak periods, particularly those with average travel speeds in the LOS E range. (The LOS E range of speed indicates slowing down of travel speeds, but with flows above stop-and-go traffic.) Hence, based on this data, as much as a third of the monitored highway system might experience congestion during peak periods.

Interestingly, the data seem to indicate more congested travel on the highways in the morning peak period than in the evening period. One reason for this is that morning inbound traffic coming toward the I-95/Route 128 circumferential route—on highways such as Route 3, I-95 South, and Route 24—experiences major bottlenecks at the freeway interchanges. However, in the evening, the roads leading away from those interchanges may only experience slowdowns somewhere further away from the core suburban Boston area and possibly outside of our monitoring area. Thus, traffic bottlenecks, especially at I-95/Route 128, have a greater impact on inbound morning traffic than on evening outbound traffic. Furthermore, morning traffic is typically less variable than evening traffic: morning trips are mostly comprised of routine commute trips to work and school; evening traffic includes not only commute trips—which tend to be less routine in the evening than in the morning—but also discretionary trips, such as shopping trips, and other kinds of trips. Evening peak period congestion levels are more variable.

Click here for Comparison between 1994–1995 Speeds Data and 1999–2000 Speeds Data

Click here for Average Peak-Period Travel Speeds on Arterial Roadways

Click here for a discussion of Traffic Volumes And Congestion Levels On Limited-Access Highways