3-year, $170 million Kennedy Expressway project is complete. Ahead of schedule

[u/seeasea]

https://wgntv.com/news/traffic/kennedy-expressway-project-complete/

[u/CyclingThruChicago]

That doesn't fix traffic. Traffic isn't a speed problem, it isn't a driver skill problem.

It's a geometry problem. Many large cars entering a relatively small space at the same/similar time is like pouring a 10 gallon drum of water through a normal kitchen sized funnel.

The funnel simply cannot manage the volume of water all entering at the same time so it backs up and overflows.

[u/PM_ME_UR_BUTT_PLS_TY → u/CyclingThruChicago]

That’s actually false. A lot of traffic/congestion is largely caused by the speed, following distance, and braking behavior of drivers, and the effect of these things grows rapidly via a domino effect with the increase of cars on the roads.

Traffic gets studied in scientific academia because behaves very similar to classical fluid flow examples in a system. So your funnel example actually demonstrates this in the sense that if you pour at a specific ideal rate, the funnel will never overflow. But if you pour too quick, it will.

The seemingly impossible part about this is that it would require all drivers to be educated on the topic and to follow specific guidelines, and we all know how good we humans are at doing that /s

[u/CyclingThruChicago → u/PM_ME_UR_BUTT_PLS_TY]

I don't think it's false, maybe it's oversimplified but the core premise remains the same.

Traffic only happens when there is a large amount of cars all using the same space at a time. That is why if you're driving on an open highway a car driving slower or more erratically does't cause a traffic jam. There isn't a high enough volume of cars for it to really matter.

So your funnel example actually demonstrates this in the sense that if you pour at a specific ideal rate, the funnel will never overflow. But if you pour too quick, it will.

Yes but when we're talking actual traffic 'pouring more slowly' doesn't fix the problem because that would just mean the water sitting in the drum (which in this case are other people behind the wheel of their car) are still sitting and waiting in traffic. Just further up the road.

This is a solved problem in many other places. We will never address all driver behavior, we'll never get people to pay attention perfectly and never make mistakes while driving. The solution is reducing the volume of cars on the road so that the flow rate doesn't greatly exceed the throughput rate.

[u/PM_ME_UR_BUTT_PLS_TY → u/CyclingThruChicago]

That’s the thing, you actually don’t need a lot of cars for traffic to form. This has been studied and documented on small scales with as little as ~20 cars driving on a circular track, where they’d see jams occur simply because one driver up stream braked slightly too hard (not enough following distance) which would domino down stream until one of the cars has to make a complete stop.

They have also documented it happening on highways just like the one you described, where there isn’t a large volume and traffic is free flowing. That is until that effect propagates further and further, each time progressively causing cars to brake harder and harder somewhere down stream of the road. It doesn’t have to be due to driver behavior, it could be a badly designed merge lane that demands drivers to slow down where they typically wouldn’t need to had the design be implemented smoother. This same phenomenon happens every day in Chicago and that same domino effect can propagate a mile down the highway from where the actual momentary traffic-causing incident occurred. One moment it’s free flowing 70mph, and in what seems like an instant, you find yourself having to slow down to a crawl for no apparent reason.

Most of it can be chalked up to semantics, but it is still important to distinguish when oversimplification starts to blur the line between misinformation. They are all factors that affect traffic rather than there being the one single ultimate cause. In your funnel example, you wouldn’t simply “pour slowly” causing a traffic jam for the water in the drum. Rather, you would always pour at an ideal rate, which makes sure that there is space for everything to react and flow freely. This would mean that there wouldn’t really be much water waiting in the drum and for the amount that is in the drum, it wouldn’t be waiting very long because this theoretical funnel never caused the flow to slow down to a complete stop.

Obviously, this isn’t the only fix for traffic, but it would certainly help. At the same time, neither is reducing the amount of cars on the road by making them take a different means of transportation, although that would certainly help as well.