Has Tuesday overtaken Wednesday as the worst getaway day before Thanksgiving? A study by the region’s Transportation Planning Board staff suggests that the answer, broadly speaking, is yes. But your individual results may vary.

The analysis is based on traffic data provided by INRIX, the company that supplies much of the information used in the highway message boards that tell you how many minutes of driving time lie ahead.

Looking at the data on the D.C. area’s traffic for November 2012, the most recent Thanksgiving period for which sufficient information was available, the researchers found that holiday travel has some impact as early as the Sunday before Thanksgiving, and that the impact continues till the Monday afterward. But the most difficult getaways were  Monday, Tuesday and Wednesday afternoon. The traffic build-up starts early each afternoon, compared to other weeks that fall.

The chart compares traffic speeds on different days before the holiday. Click here to see the full report. (Transportation Planning Board)

Tuesday from 5 to 6 p.m.  had the lowest average travel speed on the interstates and other prime travel routes, down to 20 mph below what’s considered free-flowing traffic. The report says that’s twice as bad as the speed during a typical Tuesday afternoon commute.

On Wednesday afternoon, the worst average speeds were 15 mph below free-flowing conditions. But the researchers say the drop in speeds started much earlier. Driving conditions began to deteriorate at 11 a.m. The worst conditions developed between 3 and 4 p.m.

Those are the regional averages. The study points out that drivers on some highways experienced speeds well below the regional averages. Examples include westbound Interstate 66 outside the Capital Beltway. Speeds on the 14 miles between the Beltway and Route 29 near Centreville slowed to less than 20 mph around 4 p.m. on Thanksgiving eve. During a typical Wednesday afternoon commute, the study says, the worst slowdowns were within the four miles between the Beltway and Chain Bridge Road.

On the Maryland side, the Beltway between I-270 and I-95 was among the worst stretches to travel  Wednesday afternoon. Speeds on both sides of the Beltway slowed to less than 20 mph. During a typical Wednesday afternoon commute, the study says, average speeds usually didn’t drop below about 40 mph.

Click here for the full screen version, which shows an animation of traffic speeds produced using the Vehicle Probe Project Suite developed by the University of Maryland CATT Lab. (Transportation Planning Board image)

A few other things to note in attempting to relate the regional study to your personal planning:

  • The researchers say that weather did not have a big impact on travel during the 2012 study period. Traffic officials say adverse weather can be the single biggest factor in slowing traffic. So be sure to check the long-range forecast in planning our getaway.
  • Travelers tolerate slowdowns differently. Some drivers will look at the speed averages and the impact zones and think that their experiences in those areas are much worse than the speed data suggest. Don’t make a plan based solely on a speed data chart.
  • The traffic information in the study covers major roads. You know best how crowded the local streets will be around a school or office park at holiday getaway times.
  • The information is for the D.C. region, which for many will be the worst part of the holiday drive. But long-distance travelers should make their plans for the entire route, which may be long enough to include some other city’s rush hour.
  • While the study of 2012 data shouldn’t be your sole guide in making a personal plan for 2014, it’s very helpful, So do take time to review the charts. Notice that mornings and nights after rush hours were better times to get away on each day before Thanksgiving. Tuesday’s traffic was better than a normal Tuesday until about 11:30 a.m. It didn’t recover completely until around 10 p.m. On the Wednesday, traffic was worse than normal by about 10:30 a.m. It recovered — compared to a typical Wednesday — at about 5:30 p.m. But that still meant average speeds of about 50 mph, compared to the 60 mph achieved around 11 p.m. Thanksgiving and Thanksgiving Friday were terrific days to travel, all the way through. Returning traffic showed up on Saturday afternoon and was most pronounced on Sunday between about 2 and 7 p.m., compared to a typical Sunday. On Monday, it was the afternoon rush that was much worse than a typical Monday.
  • In the time-lapse imagery for Wednesday, note the speed deterioration on I-95 south of the Beltway beginning around noon. Note also that some sections of highway got much more congested than other sections of the same highway. Look at I-270 and Route 301 in Maryland as examples.

See also
Thanksgiving getaway guide 2014