View Full Version : DC Rush Hour: am vs. pm

11-22-2005, 09:40 AM
After having had a "reverse commute" for several years, I am now, since the beginning of October, back in the position of commuting about halfway around the Capital Beltway. Even though it is still against the bulk of the traffic, it can be a tedious and unpredictable ride. I started keeping records so as to optimize my travel times.

However, I note that the morning commute is much better, and also more predictable. For some reason, the morning commute has a smaller average (40 vs. 50 minutes) and a much smaller standard deviation (4 minutes vs. 19 minutes, if you really want to know). Also, my morning drive has never been longer than 54 minutes. But the ride home last night, the worst yet, was 1:51 (!).

In no case in the afternoon drive have I come upon a lane closure for any reason, although afternoon accidents seem to be much more common than morning accidents (subjective observation from listening to radio traffic reports). Last night it was raining but there were no accidents anywhere in my travel path. DC is notorious for getting huge traffic snarls in even mildly inclement weather--you just don't even want to be here when it snows.

So is this a common phenomenon in other metro areas? Why would evening rush be so much worse than morning rush? Presumably the same number of people are driving the same number of cars each way. Do people stagger their morning drives, but everybody tries to go home at the same time? That doesn't seem likely.

11-22-2005, 09:51 AM
I'm a metro user myself (Blue Line primarily), but I'll take a crack at it. I would just guess that as the day progresses, more and more accidents happen, leading to a buildup of systematic slowdowns. Overnight the roads clear and workers are able to remove the obstructing materials, making the morning commute relatively 'systematic slowdown' free relative to the afternoon commute.

Whaddaya think?

11-22-2005, 09:56 AM
Maybe it's something like in the morning all the multiple streams are flowing out into the rivers and in the afternoon the rivers are trying to flow back into the streams. It just doesn't work as well.


John Corrado
11-22-2005, 10:10 AM
Also a DC commuter here, and I'd agree with your results: evening commutes home always seem longer than drives in.

The other thing I've noticed, which may play into it a bit, is that evening rush hour occurs even on Saturdays.

But for answers: I got nothin'.

11-22-2005, 10:12 AM
People go to work at more staggered times than they go home - some people go to work two hours early (assuming a normal 9-5 workday), some rush to get there 10 minutes before work starts. But almost everyone leaves at 5 to go home. Although this is just in my experience.

11-22-2005, 10:20 AM
Perhaps the am rush is mainly commuters to work, while the pm rush includes people with other destinations, e.g., shoppping, restaurants. That could be the same people: for example, if you drive 10 miles to work, then drive 15 miles home because you are stopping at a shopping mall, you are contributing 50% more to congestion in the pm.

11-22-2005, 10:26 AM
I live northeast of Baltimore and work in Rockville. 60 miles one way. I work 6:30 AM to 3:00PM. I usually get to work in an hour... sometimes less, and if there's an accident I can't detour around, sometimes more.

In the afternoon, I believe the fastest I've ever gotten home is and hour fifteen minutes. The longest? 3 and a half hours....

11-22-2005, 10:41 AM
Maybe it's something like in the morning all the multiple streams are flowing out into the rivers and in the afternoon the rivers are trying to flow back into the streams. It just doesn't work as well.This is an interesting idea, especially from someone in NYC who probably sees a lot of traffic. The old commuting patterns in DC were radial, with all those federal workers commuting into the city from the 'burbs. That's how the DC subway was designed, with all these radial lines. So you would think it would be easier to empty out the city than fill it up. But 20-30 years later, the patterns have shifted to include much more suburb-to-suburb commuting. Part of this is due to the development that occurs along the major routes, like the Dulles and 270 corridors.

So now there's a lot of stream-to-river-to-stream commutes as people like me take an artery to the Beltway and an artery back out to get to work.

11-22-2005, 11:13 AM
I'm a metro user myself (Blue Line primarily), but I'll take a crack at it. I would just guess that as the day progresses, more and more accidents happen, leading to a buildup of systematic slowdowns.

I'd guess this is it, and as for why the OP never saw lane closeures or the like: the DC traffic grid is like an echo chamber. Sounds keep bouncing around forever. And yes, I do mean sounds. When traffic on 495 is stopped in one place for an accident, it sends a shock wave backwards through the highway. A traffic jam that suddenly clears with no apparent cause is you getting stuck in the wave as it passes, and the wave stays around and travels against traffic along the highway until long after the actual blockage is gone.

11-22-2005, 11:20 AM
--you just don't even want to be here when it snows.

<comment on DC snow>
HEHEHEHE... I once walked the 1.5 miles downhill on Wisconsin Ave down to M ST in Georgetown, as I couldn't get a cab to turn around to take me there.

I noticed a very nice car as I left my office near the Holiday Inn, and began to walk. I stopped at 2 stores on the way down the hill (one liquor, one food) and as I approached the intersection of Wisconsin & M looked over to see the same car.

This was in about 2" of snow, at about 2:30PM. The office had vacated at 1PM with all of the staff lamenting that they'd "Never get home." As a life long NorthEaster I spent the time laughing at all of them. TWO INCHES????? We wouldn't even think of pulling out 4wd for that!

Though I loved living in DC on the company dime, some of the things that happen there are just too funny for words.

11-22-2005, 12:19 PM
My WAG is that your AM commuting time just happens to hit a 'hole' in the traffic.

I would say, contrary to what was said, that AM commute is LESS staggered then the PM. People leave their house at a certain time as not to appear late to work. Leaving work, however might involve early leaving once work is don't and nothing more can be done in the time left, to people working late to finnish a project.

PM commutes is when errands enter the picture, which disrupts people's driving routes and people drive distracted trying to plan their route, tired from the work day and hungry for dinner.

AM commute people drive single purposly, knowing where they are going, are well rested and (should be) well fed.

11-22-2005, 01:17 PM
Hmm. In my experience the Am commute was much worse than PM. Maybe it's because I tended to leave a little late (6:30-ish), but it rarely took me less than 1:20 to get in to work downtown and rarely more than 45 minutes to get home. I always assumed it's because the huge number of government workers who tend to leave, on average, earlier than those in the private sector, lengthening but thinning the afternoon rush.


John Corrado
11-22-2005, 01:17 PM

I don't think that staggered times really plays into it; people who come in earlier (or later) are pretty likely to also leave earlier (or later) by about the same margin.

I also can't see anything with it being the problem of one route being more amenable to traffic. In a perfect situation, all commutes would be absolutely symmetrical; whatever situation occurs at 8:00 AM on a certain road would be exactly replicated at 6:00 PM on that road with traffic simply on the other side of the divider. If the roads themselves were asymmetrical and poorly able to handle traffic in a certain direction, I suppose that'd be possible, and that may be the case.

But I think the suggest of "because not everyone on the road in the P.M. is coming directly home from work" may be the best. Very few people are going to be entering commuting lanes at 7-8 in the morning to go visit friends, grab groceries, or do Christmas shopping. But lots of people are going to be entering commuting lanes at 4-6 in the afternoon to do those things. It may only be a few cars more, but only a few cars would be enough to increase the chance of accidents and lessen the overall speed.

Edward The Head
11-22-2005, 01:20 PM
That's really odd since I live up I-270 and have found for the most part that the morning is the worst. I usually take the MARC train but when I swim Iris takes me to work. It almost always takes us 40-50 minutes to get to work, even the HOV lanes have slowed down in the last couple of years. In the afternoon I have found that using the HOV everything slows down in the same places and it moves, rarely does the HOV stop.

However, rain like last night really screws things up. I will admit that it's harder to get home when it rains, but for the most part I can get home faster then I can get to work.

An Arky
11-22-2005, 01:22 PM
There's also more business-related travel going on - delivery trucks, contractors, people coming back from client meetings, etc., in the afternoon than early in the morning.

11-22-2005, 02:29 PM
I'm going to "third" the notion that the AM is primarily commuter traffic and the drive home is the same volume of commuter traffic AND other kinds of traffic.

Small experiment to check this: notice how many cars have single occupants (seems like 100% some days) in the morning compared to the evening.