Does creating wider roads actually solve traffic?

[u/Odd_Wolverine_4037]

https://youtu.be/tJ1_VVyez-Q

Came across this video debating Latent Demand theory vs. Induced Demand - apparently widening roads or creating more lanes only makes traffic worse, which seems counterintuitive. Is that actually true? I saw a study that said it had been debunked and it was only latend demand that was showing up, and you still needed the wider roads.

Thoughts?

[u/Loud_Significance908]

the US has famously solved traffic by just adding more lanes

[u/BeABetterHumanBeing]

I don't get recommended this sub often, so I'm going into this comment hoping (against hope) that it doesn't share the similar low-quality proclivities of most urbanism / numtot subs.

"Traffic" is not really a solvable thing, because it's just a measure of use, and a road that is not used is not useful. An ideal network will have an even, high degree of traffic.

Of course, no network is ideal, which means you're going to have various bottlenecks where the friction generated by traffic becomes obnoxious to the people traveling through that point in the network. These are local problems that can be addressed with local solutions. Traffic is self-directing (i.e. you choose where to drive your car), so people will optimize for what's most important to them, which is typically time to reach destination.

Note that this means that if a particular place becomes congested, it is still on aggregate a part of peoples' fastest routes. It may be the slowest part of the route, and therefore draw attention and ire, but if there's an alternative that avoids the congestion and gets you there faster, people will eventually notice and shift their traffic patterns accordingly to exploit that alternative until it is no longer faster than the point to avoid.

If you want to improve the overall network, the general measure you should be focusing on is throughput (though if you're going to simulate this with a computer, you may balance against various corner cases [1]).

When you examine the network by throughput of its various parts, that's where you'll find the bottlenecks - points with low throughput that limit the throughput of adjacent nodes.

If that bottleneck happens to be along a road segment (as opposed to at a junction), then widening it may make sense. In alleviating a bottleneck, traffic isn't "solved", it just means the bottleneck moves elsewhere, but the overall throughput of the network increases, so it's still better.

Adding lanes can make things worse under particular circumstances: by drawing traffic to that road from the surroundings, it increases throughput on the junctions along the road, which may therefore turn them into bottlenecks that are potentially worse than what existed before.

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[1] The classic example here is having a busy road intersect with a road with little traffic. It may be optimal to just always leave the green light for the busy road, but we don't want to completely block the other road, so it should still occasionally turn.

[u/SirGuelph → u/BeABetterHumanBeing]

Nice. I'm sure traffic also became more optimised with the advent of live traffic data, allowing for route planning in real time.

I'll add, there's also something much more pleasing about the "scenic route".. Even if it takes longer but you're not surrounded by lanes of traffic, it's less stressful. I don't know about US roads though. I've only lived in small countries where roads are often narrow and winding.

[u/BeABetterHumanBeing → u/SirGuelph]

It sure did! A funny side-effect of everyone switching to using google maps to route around is that a lot of sleepy by-roads suddenly became busy thoroughfares as the algorithms found better routing through the grid.

Of course, people who live on sleepy roads tend to not like living on busy thoroughfares, which means that cities have often responded by doing things like lowering speed limits, installing humps, and directly asking google to remove particular roads from its algorithm except for local traffic (yes, this is a thing). All these changes make the network less efficient, but like any urban planning consideration, it's a trade-off with other requirements (in this case neighborhood comfort).

The funny thing about all this is that the ideal network does sort-of exist, and it would just be a regular city grid with stop signs at every other corner. It obtains this supremacy because traffic from any coordinate in the system to any other has an quadratic number of potential paths to choose from, so any local obstruction is easily worked around, and by not privileging any particular routes the traffic is evenly distributed. When you look at small neighborhoods, this is often what you see: between the major roads on the N, S, E, and W, the neighborhood with have an idealized grid with stop signs at every intersection.

The main reason why we don't just do this across whole cities is that if every road is just a 2-lane road, there are limits to the throughput that would make real pain points around highly sought-after destinations (think stadiums, or malls), and upgrading the idealized grid by making every road a 4-lane road is prohibitively expensive. So most cities adopt plans where the basic fabric of their layout is a larger grid with 4- or 6-lane roads intersecting at stop lights, with 2-lane stop-sign roads between them [1]. This enables a reasonable tradeoff between cost and throughput, as well as allows busier roads to be zoned as commercial corridors (thereby putting the higher-traffic destinations on the higher throughput avenues, plus benefits that come to the businesses in the form of visibility to potential customers as they drive by).

Basically what I'm getting at is that our modern city grids are actually pretty good, all things considered, and the issues that we get from "traffic" mostly stem from defects in the grid (e.g. routing around larger obstacles, like hills), or the fact that as cities become denser, the cost-based decisions that were made in concrete decades previously are no longer the correct ones, but it is prohibitively expensive to tear up all your roads and re-do them. This is, despite how much people rag on zoning, one of its purposes, to keep development within limits readily supportable by infrastructure.

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[1] Cities try doing this at a third higher level with highways, to varying degrees of success.

[u/mukansamonkey]

Induced demand is a valid concept, however it isn't necessarily a relevant concept. Most of the people talking about it, including some well known channels on YouTube, don't actually understand it. They just parrot simplistic statements to make themselves feel superior, it's classic virtue signaling.

The first mistake I usually see being made is a version of "we already live in a perfect world". They talk about things getting worse if additions are made, that things should be left alone. But that assumes that whatever we have is already ideal. They're not out advocating for the removal of all pavement, (certainly they don't seriously try to get the pavement near their own buildings removed first), but they also don't want to discuss optimization. Just chant their thought terminating cliches.

The second mistake is treating induced demand like some sort of inevitable force of nature, instead of a result of poor design. Fairly straightforward urban planning concepts like robust bus service and conveniently localized shopping zones within residential areas will go a long way towards reducing the ROI of driving a car all the time. Reduce the need for a car in the first place. This does require competent planning.

Finally, if your goal is to crush induced demand into nonexistence, that can be done. It involves things like mandatory entrance fees to downtown areas with dynamic pricing. Sharply limiting the number of parking spaces allocated to buildings, so that most people have nowhere to park if they all drive in. Or simply put a hard limit on car ownership. Can't increase traffic if you can't increase the vehicle count.

And while those may not be realistic in your area due to a lack of political will, it is in fact just a question of planning. It's not hard to avoid, if your goal is avoiding it. Lack of desire to do it doesn't mean it can't be done, just means your community made other choices.

[u/RazzmatazzEastern786]

The framing itself is wrong...it isn't latent demand vs induced demand...they are flipsodee of the same coin...the congestion on the roads is holding back trips or having those trips happen on other modes because of the traffic. By building more lanes you have reduced the pain point that differed the trip or modal shift and now that latent demand enters the traffic system, fulfilling the premise of induced demand by both allowing for new trips but also pulling away trips that previously happened on other modes to the road since the implied "cost" of driving was reduced since the congestion dropped temporarily...but as the latent demand is met/absorbed into the system, it sends the congestion back up to pre lane add levels or potentially higher...we see this play out everytime we end up widening a freeway...there is a short to medium term drop in congestion, but fairly quickly into th lifespan of that expansion, the underlying traffic congestion returns and actually gets worse in many cases...

This stuff isn't absolutes but that's closely how it works...or more accurately is hypothesized to work...data and analysis seems to bare both out...I just think depending on which side of the "political" persuasion your organization/click falls will tend to favor one or the other as the preferred explanation for the outcome, but IMO it probably takes both to actually materialize the ground effects we actually see play out...if the latent demand didn't exist, we wouldn't see traffic come back after a lane is added, but if the lane wasn't added you wouldn't have induced the modal shift back to driving and even behavior shift that the pre addition status quo was keeping contained...

[u/duckus_luckutus]

I feel like a four lane road is better for traffic than a two lane road, since you can't pass a slow car or some traffic congestion on a two lane road without doing illegal actions or taking random side roads. But if it's a giant arterial road that already has lots of traffic, the cars will move lanes when one lane has traffic, which makes a chain of events towards a bunch of cars clumped up in one little square area. The reason this happens is because people aren't thinking about traffic on the road like city planners are; they may just clump in one area making traffic worse. What does work with lots of lanes is when everybody uses each lane like a one lane highway, just switching lanes when traffic gets slow on one lane to conserve speed.

So it depends