A few weeks ago, a construction project began on the eastbound portion of the Alexander Hamilton Bridge, which brings cars from Manhattan (New York City) to the Cross-Bronx Expressway, reducing the traffic flow to only eastbound lane. This project is expected to take six months.
Anyone who knows anything about traffic in that area is familiar with the idea that just one minor accident on the Cross-Bronx can snarl traffic for many miles in all directions, and so no one was surprised to hear dire predictions that this construction would cause traffic to be backed up not only through Manhattan and the George Washington Bridge, but possibly possibly as far back as Hackensack. See, for example, this article.
But this failed to happen. Just a few minutes ago, at 7:30 AM, the traffic report on the radio reported a 10 minute wait at the Lincoln Tunnel, but zero at the George Washington Bridge. Why is this? I know that there is a bit less traffic in the summer, but narrowing the four lanes down to one ought to MORE than make up for that, right? What am I missing? Why is the traffic okay?
I meant to add: – I suppose many people are taking other routes to avoid that area, and that MIGHT explain why the traffic was okay for the first day or two. But we are now a week and a half in, and these adjustments should have worn off by now. Even people who did take other routes would probably have gone back to their regular route because of the lack of traffic, right? And it shouldn’t have made such a big difference to begin with. I mean, from four lanes down to one is a BIG traffic jam, even in the best of situations.
Please, can a traffic engineer fight my ignorance? Which piece of the puzzle am I missing?
Traffic is a weird animal and acts unpredictably. One factor may be that people took alternates, but I don’t think that is enough in itself as those alternates frequently auto-jam themselves when traffic is diverted to them.
Another factor is that additional lanes don’t add as much capacity as you would think, and less lanes means less options and less switching. Switching lanes tend to slow down all lanes to the slowest one, so with less options available to switch traffic can flow better. I also believe part of the plan here is what is called a one lane ‘cattle shoot’, a single lane without any lane switching options due to barriers installed. Unless someone breaks down these normally move the fastest in high traffic conditions in my experience.
Traffic is generally lighter in the summer, and the rush hour traffic gets spread over a longer time period as people change schedules to get more ‘sun’ time. I’ve made surprising time in and out of Boston lately. If these traffic flow conditions are still in place in September, expect the Cross Bronx and all routes leading to the GW to turn into a giant parking lot. Still, I’d rather go through that than try and take the LIE on an average day during rush hour.
Bingo! (except that the correct spelling is “chute”.)
When I first read your comment, my reaction was that (in my experience) traffic flows nicely AFTER all the lanes have merged, but there can be problems for miles prior to that point, with everyone jockeying for a good position while the lanes try to merge. But then I decided to look it up, and found that, speaking about actual cattle, Wikipedia: Cattle Chute says (emphasis mine):
And it turns out that this is indeed part of the plan for the Alexander Hamilton Bridge, in stages 4 and 5, as reported in this schedule on the NY State D.O.T. website.
[rant mode on] I think the people at the Garden State Parkway need to learn about these cattle chutes. I like that each toll collection area is now only one direction or the other, but the lanes seem to be designed with curves which encourage cars to move forward in an UNcontrolled manner, with drivers wildly switching lanes because the cash and EZpass lanes are not where the drivers expect them to be. [rant mode off]
OP, I think that you would be interested in reading Traffic, by Tom Vanderbuilt.
It turns out that a lot of what traffic flows do is counter-intuitive. He addresses the type of situation that you mention. Apparently, a lot of people think the same way, so they either take a different route, or possibly a different mode of transportation, or just simply stay home. The result is that traffic during a time of disruption sometimes actually turns out to be lighter than normal, not heavier.
Back to the OP: What I’ve found is that whenever a lot of notice is given about a major traffic disruption, problems turn out to be much less than predicted. Witness “carmaggeddon” in Los Angeles not long ago.
Also there was quite the opposite when these things were not announced. When EZ pass came to NY, they knew there would be traffic troubles, but after the event they admitted that they would underestimate the delays reported and would not report delays of more then a hour wait (they would only say it’s a hour delay even if it was 2 hours.). This transition to EZ Pass was perhaps one of the worst traffic nightmares in the NYC area.