Comment by legohead | Hacker News Reader

Comment by legohead | Hacker News Reader

I've been intrigued by traffic after moving to SoCal from Oklahoma. day after day you will hit pockets of slowness only to find out there was no obstruction.

in the past I read about 'shockwaves' in traffic. one guy changes lanes too fast, which causes multiple lanes to hit their brakes, and then you get the shockwave effect ("Jamiton" in this article) and it lasts a long time. but after doing enough highway driving, I don't think that's the main issue.

my hypothesis is it's simply merging traffic. I've noticed on my daily routes that traffic is always bad where there are a bunch of roads merging, and immediately after all the merges finish, traffic speeds way up. bad drivers aren't causing these shockwaves, it's all the sudden merging. I attribute this to bad planning. "hey, this is a major road and it's going across the highway, it should probably have a merge here."

a lot of people bring up zipper merging - better training of drivers will help a bit, but properly planned highway merging would be much more efficient.

Yes. The Highway Capacity Manual is a compendium if work by the traffic engineering professionals that examines data and observations to develop theories and approaches to traffic.

If you have a freeway with no on ramps nearby (usually 6 miles) then you should be free of traffic issues if the roadway throughput (1,500 per lane per hour), if it goes above that then crazy agents in the traffic do not allow for distances between vehicles and the brake of one individual creates a cascading effect. This is one cause of back ups.

The next is if you have an on ramp on said freeway, there must be enough capacity for the freeway to absorb those vehicles in. Additionally, you need to have space and time for the vehicle to merge in. If the driver does not feel safe or have enough distance, they will perform erratic moves to get on, which will slow down traffic in the aforementioned cascade.

If a highway on-ramp is failing, it is usually due to a political person pushing for it. The Federal Highway Administration (FHWA) has a long list of requirements for a new ramp, and they are very well thought out to prevent issues and are good to work with.

I've found that a lot of times it's not an onramp merging into you, it's people waiting until the last second to merge to an offramp and slamming on the brakes and/or cutting off someone to not miss the exit.

I deal with this every day when I come home from work on my exit off the 405. People don't want to wait in line because it's slow, but it's slow because those people cut in at the last second and cause the entire lane to apply the brakes.

The 405/55 interchange is another example of that, particularly 405N to 55N in the evenings.

You are absolutely correct. In my experience, traffic is caused by drivers who 1) refuse to plan ahead and 2) are fine with fucking over other people in an effort to mitigate that lack of planning ahead.

You're being generous by saying they "refuse to plan ahead". I think they are actively planning to "cheat" and cut in line, thus screwing over all traffic behind them.

I deal with a merge every day where 3 interstates come together. The first two (I64E, I195N) run together for 1/2 mile and finally merge from 2 lanes to one just before they merge into a dedicated lane on the destination interstate (I95N). They recently (last year or so) added the dedicated merge lane on I95N to try to speed things up, but it has not helped. The real problem is people waiting until the last second to merge 2:1 for the merge on to the destination highway.

I think things would be more effective if traffic from both interstates were forced to merge to a single lane as early as possible. Then traffic would be moving at close to the speed of the destination highway, rather than at 5mph due to all the lane jockeying resulting from the 2:1 merge just before the final merge onto I95N.

What I see here in Maryland is that there is plenty of room for every car to merge onto the highway, except that nobody moves left to let them in. Why would you stay in a lane where you can see you're going to be slowed down and even have to brake, when you could move over, maintain your speed, and make room for others? I don't know, but that seems to be the majority's instinct.

Perhaps they are waiting for the next exit. Then they'd be moving out and then coming back in. Going slowly but guaranteeing your slot in to your exit is better than keeping speed and not being able to get back in.

You can't trust the other traffic to give you room. After all, you look like a guy who just decided to overtake one exit before his own.

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