Optimizing the traffic

October 22, 2018 7:45 AM

How would you handle these traffic lanes on my commute? It’s a bridge with three lanes. Starting, it’s one left and two rights. The one left then becomes two lefts. I need to turn left. It’s a very short light. When I start out on the far left, I’m stuck on the bridge for 30-40 minutes, at a crawl.

When I’m in the center, I move at a faster pace then need to cut and sneak in when the one left becomes two lefts or earlier. But then I feel guilty because I know how bad the far left lane is and how everyone is waiting.

What I usually do is start in the center lane, fly down til the middle of the bridge, then merge to the left. Then I am grumpy as people cut me off but feel like I’m being a good citizen in my correct lane. Absurd. I know.

FYI for those who know, this is the Key Bridge from VA to DC.

posted by inevitability to Grab Bag (11 answers total)

I completely understand where you are coming from, but I am under the impression that the optimal strategy for total traffic flow in a circumstance like this is a late zipper merge. There are a bunch of googlable articles on the topic.
posted by JPD at 7:53 AM on October 22, 2018 [5 favorites]

Yep, late zipper merge. Just because other people don't understand why zipper merging is the best, most efficient solution, doesn't mean you should not do it. In fact, the more people who do it, the more chance there will be that others will also do it, shortening the time-to-turn for everyone.
posted by seanmpuckett at 7:58 AM on October 22, 2018 [1 favorite]

I don’t suppose there is an alternate route? I have a similar situation on my commute that I replaced with a slightly longer route, as I realized over time that avoiding the mental and physical stress of the intersection was worth 5 minutes a day.
posted by q*ben at 8:02 AM on October 22, 2018 [2 favorites]

Make everyone else's commute as miserable as possible. This effectively prices their commute higher. Which, on the margin, will push a few drivers onto the metro (maybe). Which, given that all these folks are car-commuting into one of the few cities in the US with passable mass transit options, is really a public service. Late merge - it's good for you, it's good for the planet.
posted by everythings_interrelated at 8:17 AM on October 22, 2018 [1 favorite]

If you're interested in optimizing for traffic, a late zipper merge is your best option - not just for you, but for everyone.
posted by saeculorum at 8:19 AM on October 22, 2018

Another vote for late zipper merge ... it's the right thing, even if people don't realize it.
posted by mccxxiii at 8:34 AM on October 22, 2018

Response by poster: I get so anxious about late zipper merges! How do you all do it??
posted by inevitability at 8:37 AM on October 22, 2018 [2 favorites]

I decrease my anxiety about late zipper merges by always having a backup plan. If someone doesn’t let me in, I either slow rapidly and pull in behind them, or keep going in my current lane and take an alternate route. If there is no alternate route I merge early and wait with as much patience as I’m capable of.
posted by dttocs at 8:59 AM on October 22, 2018

Do not accept personal responsibility for sub-optimal traffic design. Always give a thank-you wave even if the person who lets you in scowls. As more people clue in and use the late merge, justice will again be served. See, you're a leader, a teacher, an example-setter.
posted by theora55 at 9:27 AM on October 22, 2018 [2 favorites]

Not all merges are equal. I totally understand your stress in this situation. A classic “zipper merge” situation involves two lanes merging, which means that everybody’s waiting for the same thing. In this kind of situation, where you’re trying to get into a different lane with a higher demand, if you can’t get over immediately you’re blocking a lane of traffic that would otherwise be freely moving. I’m guessing that since another left lane is added you can usually avoid blocking the right hand lane by merging over when the capacity increases.
posted by q*ben at 10:53 AM on October 22, 2018

Zipper merge is often cited as some miracle of traffic management but it only works in some limited circumstances. If you have a lane with traffic capacity of 1000 cars per hour and 2000 cars per hour are trying to use it, a zipper merge does nothing to increase capacity.

If the lane you want to merge into is moving and there is space to merge without anyone in that lane having to brake in order to let you in, then your merge is not disruptive to the flow.

But if the lane you want to merge into is stopped or moving very slowly, then merging late does nothing to help the traffic flow. You are just cutting in front of others and causing more congestion because others have to brake to let you in. Plus, as you slow down to wait for room to merge left, you are blocking straight through traffic behind you.

So it really depends on circumstances. If you can look ahead and see the lane you want to move into is stop and go, as for a traffic light, you should merge early, not late. And if you misjudge the traffic and find that you don't have a slot to merge into, never slow down to wait for an entry. Just keep going straight. Otherwise you are blocking straight traffic.
posted by JackFlash at 11:53 AM on October 22, 2018 [9 favorites]