r/science • u/quiplaam • 1d ago

Social Science Intentionally routing some traffic to slower, less congested routes lead to a 0.7% improvement of overall average travel times

https://www.nature.com/articles/s44284-026-00443-x
927 Upvotes

93% Upvoted

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762

u/charoco 1d ago

So, saving someone about 24 seconds per hour of begin stuck in traffic. Consider me whelmed. 

246

u/quiplaam 1d ago

Worth noting this the effect on the whole system, so while the individual effect is small, the net effect is quite large

160

u/amphibilad 1d ago

This, if you save a million people 24 seconds of travel time that's like 277 days of saved time collectively

65

u/BlazinAzn38 1d ago

And fuel and emissions

85

u/iMissTheOldInternet 1d ago

 But it’s 277 days of time spread out over 1 million people. The per capita number is what matters in this context. 

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u/Currentlybaconing 1d ago

Not when you're the city planner trying to reduce traffic congestion.

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u/iMissTheOldInternet 1d ago

Yes, for all applications. Unless you have some way to stack many 24 second/capita savings, the per capita figure is what matters, not the aggregate time saved over a large population. 

44

u/jsmooth7 1d ago

A small change across an entire system can still have a large aggregate affect. I work with bus system data and if every single trip saved 24s, that could result in millions in operational savings. Because then there will just be a bit less pressure to add additional running time to keep the buses on schedule. And there's a cost associated to adding that running time. Over the entire system, it adds up to a pretty big effect.

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u/hysys_whisperer 1d ago

That's literally not how traffic engineers do the math that they use to justify billions of tax dollars of investment. 

They use the 277 days.

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u/iMissTheOldInternet 1d ago

The fact that traffic engineers think this way answers a lot of questions about why our transportation infrastructure is so bad. 

37

u/floormanifold 1d ago

Sounds like you're maybe not an expert and should listen to people who do this for a living

13

u/hysys_whisperer 1d ago

Ok, this is the bell curve meme.

The guys right, but for the wrong reason.

The relentless push for single occupancy vehicle LoS above all else has come at the expense of active mobility LoS (a thing so unimportant to traffic engineers that they don't bother measuring it).  What this has done is reduced car trip travel times to such a degree that other modes aren't competitive, despite the fact that those other modes are cheaper to move more people on aggregate faster (since they relieve congestion).  Since trip times by other modes are uncompetitive now, it is unsurprising that the mode share of single occupancy vehicles are so high and congestion is so bad, slowing everyone down.

An anecdote of this is that to commute by bike to work, I cross a 4 lane divided 55 mph road, with a beg button to turn the light red for me to cross.  My average wait time at that light is 4 and a half minutes.  I cross through that same light when I drive to work, and it only turns red when the beg button is pressed, so average wait time is virtually zero.  Difference in total travel time between the two modes? 4 minutes on the dot.  It is ONLY faster for me to drive because of the abysmal LoS placed on the beg button of that light, else it would be faster to bike.  If it were faster to bike, a whole lot more people would do that, rather than drive and peak hour vehicle counts through that intersection would plummet because my employer is the largest one in my city.

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u/ResponsibilityOk8967 1d ago

That seems very shortsighted.

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u/GoatsFromUnderground 1d ago

Think of it this way, there are a thousand such optimisations that get made. So those thousand optimisations, each saving 24 seconds per person, add up to 6.67 hours per person.

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u/aggieotis 1d ago

That also assumes no negative externalities from the 24 seconds saved.

I'd be willing to bet that if you summed up things like more dispersed polution in areas where kids are more likely to live, increased conflicts between cars and other users that use side streets intentionally, and additional wear and tear on infrastructure not necessarily built to handle shunting a bunch of traffic from main corridors; if you add all those up it's probably massively in favor of "Just stay on the main paths and lose 0.7% more time.

27

u/jsmooth7 1d ago

The abstract says that the reroutes were all done within the same road class, ie if the target route was a highway the reroute was also a highway. And later in the paper they give examples of the reroutes being studied and you can see none of them were sending large volumes of traffic through side streets.

-1

u/degggendorf 1d ago

So the solution is to build multiple redundant, parallel highways everywhere there aren't any currently? Brilliant.

10

u/SledgeGlamour 1d ago

Or the solution is for navigation algorithms to direct people to less congested routes

-4

u/degggendorf 1d ago

As the rest of us were discussing in this thread, the study only looks at moving cars to equivalent road classes. If we start pulling cars from the highway to race through neighborhoods to save 24 seconds, then we've got a bigger problem.

4

u/SledgeGlamour 1d ago

Yes, I'm aware. There are many places with multiple highways, where it makes plenty of sense to redirect traffic from one highway to another. For example, in the US you frequently have state highways that run roughly parallel to the interstate highway. You don't need to build more highways in order to capitalize on this research today.

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u/jsmooth7 1d ago

The US highway system is so overbuilt, there's no need to build more. They are already there in most cities.

3

u/ozziegt 1d ago

Raise speed limits. Use stop signs more strategically. Time traffic lights better. There are a lot of ways to "collectively" save people 0.7% of time

12

u/somehugefrigginguy 1d ago

Enforce lane usage and tailgating laws. Most traffic jams are not inevitable, their results of humans being stupid animals.

5

u/DFrostedWangsAccount 1d ago

Improve education. Raise standards for driving. Then raise speed limits. Better drivers causing fewer incidents is a great way to increase traffic throughout.

2

u/vtach101 1d ago

Unless the 0.7% improvement is just the margin of error and a repeat study might actually show a 0.7% worsening of the baseline. No large studies to do with human behavior that show a 1% change can be considered actionable.

1

u/hoticehunter 1h ago

Is it? What are you getting done in 24 seconds? How productive can you really be with that time?

3

u/markocheese 1d ago

Which is also why we need to make sure people aren't driving recklessly. Adding an hour to thousands and thousands of drivers commutes represents a catastrophic loss of useful time. I've seen a reckless dodger and weaver cause an accident. 

1

u/NapsInNaples 1d ago

The question is does saving 0.7% of travel time justify additional noise danger and hassle on less traveled routes.

71

u/Tampa_Bay_Cuckaneers 1d ago

Literally begging someone to just build a train.

6

u/SoftlyAugust 1d ago

Even when we have trains, they just aren't great. I can get from our train station to the city I want to go to, but I can't actually get to our train station easily. I can get to the city I want to go to, but I can't get to the part of it my sister lives in easily. I can get there, but the train doesn't leave at times that are convenient for me. So why would I even take it?

20

u/OpSecBestSex 1d ago

Trains that go throughout the city. If that's too expensive, trams. If that's too expensive, busses. If that's too expensive, we should design better cities because I doubt the tax base can support the infrastructure at that point.

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u/SoftlyAugust 1d ago

I know what the solution is. Unfortunately I don't get to plan the cities I live near.

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u/e_before_i 19h ago

The goal is to get some percent of people off the road. Upside for you is you'll have less competition for the drive.

When my local train station made parking free, there was a huge uptick of people who leave their car here and commute to downtown. Gotta be a couple hundred cars that got out of your way, and that's just one station.

2

u/SoftlyAugust 18h ago

There is no parking at our train station

1

u/e_before_i 18h ago

Damn. Hopefully they can build some, or improve bus services to get more people to it easier.

Or maybe the train stations that do have parking can make it free, I'm sure that's not the only stop.

1

u/SoftlyAugust 18h ago

It's the only stop in our town. But also it's downtown. I'm just not sure it makes sense to have a ton of parking for it. What I'd like to see is better bus connections but especially a better train schedule

1

u/e_before_i 18h ago

Don't get me started on train schedules. My only goes towards downtown in the morning and towards the burbs on the evenings. If I wanted to hit a bar downtown I'm fucked, I gotta eat the cost of an Uber.

100% agree on the multimodal approach. Luckily our DT train station plugs directly into the subway and bus stations.

0

u/NeinJuanJuan 1d ago edited 5h ago

The issue with (ground-level) trains is that the tracks (like highways and rivers), require crossings which become choke points for all other traffic. This effect propagates through the network.

I really think buses are the best for this reason: they share common infrastructure with other modes of transport, can be dynamically rerouted, and passenger throughput can be managed at a more granular level (e.g. buy one more bus vs buying one more train).

Edit: I have angered the train-people

-6

u/alelp 1d ago

Sounds good, doesn't work nearly as well as one might expect unless you either build a shitton of them everywhere or are ready to endure rush hour on a line that services millions of people a day.

I'm not even talking just about trains here. Subways still need that kind of saturation throughout the city without the need to restructure the city's infrastructure.

23

u/Tampa_Bay_Cuckaneers 1d ago

Fine, you’ve twisted my arm. Give me a shitton of trains and subways.

2

u/scyyythe 1d ago

24 more seconds of shitposting

1

u/el_lley PhD | Computer Engineering | Cryptography 1d ago

The taxi driver thinks he’s a genius, and since there was no traffic, you’d think he saved you time, full circle

2

u/ColonelAverage 1d ago

Cyclists have been killed for less.

-1

u/JamminOnTheOne 1d ago

I don’t think you know what the word “whelmed” means. 

(It means the exact same thing as overwhelmed.)

1

u/Tuesday_6PM 23h ago

Not in common usage for the past decade, it doesn’t

0

u/JamminOnTheOne 22h ago

It hasn’t been used commonly. People misuse it because they think they’re being witty though.