Chart shows five years of pre-Memorial Day traffic patterns. The higher the line, the slower the traffic. (Transportation Planning Board)

Thinking about getting ahead of the crowds and launching your Memorial Day weekend trip on Wednesday or Thursday afternoons?

Not so fast.

Really, you won’t be going fast at all, according to researchers with the D.C. region’s Transportation Planning Board. Wednesday and Thursday afternoons are two of the windows of opportunity that drivers should shut right now. Their families will thank them.

It’s not like Friday afternoon has become a good choice. (It’s amazing how many people can drive around here.) Friday afternoon just has a lower worst-of-the-worst point than the previous two afternoons. Before Friday, the early getaway drivers are mingling with people who are still just trying to get home from work. By Friday afternoon before the long weekend, much of the getaway traffic already has gotten away, though there still are enough drivers left to slow traffic.

So if you’re trying to avoid that kind of traffic, what’s left? The researchers suggest late Thursday or early Friday. (I think an early Friday getaway works on most weekends, not just Memorial Day. The Friday morning rush is often always the lightest of the week, at any season.)

The planning board’s researchers have now looked at the Memorial Day traffic pattern from 2011 through 2015. But keep in mind that they’re looking at highways regionwide. They remind us all that our results may vary, depending on the particular route we take and the weather. “Day-of weather conditions can affect traffic in real-time, while weekend forecasts can impact how many people head for outdoor destinations like the beach or mountains,” they write in their analysis of the traffic data.

The company that operates the 95 Express Lanes had its own findings about good and bad getaway times, based on last year’s first experience for those HOT lanes with the Memorial Day getaway. This is attention-getting because I-95 travel between the Capital Beltway and Fredericksburg is almost always the worst of the summer getaway traffic. Folks who go through the I-270/70 bottleneck in Frederick don’t know what they’re missing, fortunately for them.

The busiest travel times on the regular I-95 lanes and the 95 Express Lanes before Memorial Day weekend in 2015 were Thursday and Friday between noon and 6 p.m., the express lanes operator said. Friday was the worst of those two days.

“To avoid higher-than-average tolls and peak traffic, drivers should depart before noon on Thursday or after 6 p.m. on Friday,” the company said in an advisory.

There’s some more specific advice below about this heavily traveled route, but let’s go back for a moment to the regionwide view from the Transportation Planning Board study.

The measure the researchers used in the chart at the top of this posting is the Travel Time Index, a widely used gauge of delays. Over the last five years, the researchers found, the average Travel Time Index for the pre-Memorial Day peaks ranged from 1.5 to 2, which meant that on average, it took 50 percent to 100 percent longer to reach destinations than on a day with no traffic. When they looked at particular routes at particular times of day, the index sometimes would reach above 4.

The five-year chart also shows how the magnitude of the traffic delays varies over the years. They can see when the traffic is likely to be bad, but they can’t tell you exactly how bad it’s going to be from year to year.

One is extreme year-to-year variability in the magnitude of traffic back-ups on Thursday afternoon, which makes it hard to predict how bad traffic will actually be. In 2014, for example, the Thursday before Memorial Day turned out to be the worst traffic day of the entire year. In 2015, Thursday was still bad, but at its worst point was still only about half as bad as 2014.

They aren’t sure what is responsible for that year to year range. Could be crashes, could be road work, or weather conditions. Or something else.

One trend to watch out for if your must leave on Friday: The slowdown tends to start earlier than on the other days. It usually shows up around 11 a.m, peaking in mid-afternoon and remaining bad until about 6 p.m.

The sweet spots: The researchers said that over the five years the Thursday afternoon rushes have ended around 8 p.m., and then the traffic doesn’t really pick up until that 11 a.m. surge on the Fridays.

95 Express Lanes tips
The Virginia Department of Transportation plans to extend the express lanes two and a half miles farther south, to get past the bottleneck around Garrisonville Road, but drivers won’t get that benefit in 2016.

So if you are heading south in the express lanes this weekend or anytime this summer, watch for an advisory sign before the Quantico/Joplin Road exit that will alert you to delays ahead. You then will have a chance to exit the express lanes at Joplin Road. If the delays are really bad, the sign will encourage drivers to bail back to the regular lanes at Joplin Road.

Getting into the regular lanes won’t solve your traffic problem. If there are delays in the express lanes, there will be delays in the regular lanes. But if you are in the express lanes and you don’t have at least three people aboard with your E-ZPass Flex set to “HOV,” you’re going to be paying an outrageously high toll just to sit in that traffic. At least there’s no extra charge in the regular lanes.