Data on Beijing Cabs Reveals the Cause of Traffic Jams | Hacker News Reader

Data on Beijing Cabs Reveals the Cause of Traffic Jams

technologyreview.com

35 pointsAnon8428 comments

The construction of bigger roads is the CAUSE of traffic jams, not the solution. The more you improve a highway system, the more people build and relocate to take advantage of the highway. But you can never upgrade the rest of the city streets to absorb all the cars spilling off the highway. The only solution is to invest in mass transit and vigorously control suburban sprawl (by increasing population density, making downtown living more attractive, and restricting new development anywhere within driving distance).

That's not a solution, that's giving up and saying "we won't let you live there".

My experience is the opposite anyway - the more sprawl the less traffic. Very congested areas with tons of people were always horrible places to live, never a place to park, and it takes forever to get anywhere. (And please don't tell me your "solution" to that is making it so people don't want to go anywhere because it's too much trouble.)

Putting underground subways like some cities have is simply unfeasible in most places. Buses are just too slow in congested areas.

If you're living in a very densely populated area and you "never have a place to park", you're doing it wrong.

(To be clear: what are you parking? The whole point of a densely populated area is that you don't need a vehicle.)

But I do need a vehicle - you try going grocery shopping with a bunch of kids and bringing back 10 or more bags without a car.

I do know there are people who manage it, mainly by shopping almost every day, or by buying from stores very close to the house (and paying extra and dealing with a low selection).

But, mass transit is not a complete solution. There are other use cases which you are not taking into account.

I find very spaced out living, with a car, to be best. Ideally you have a centralized shopping area, so you only need to make one trip and get everything. (And of course no houses anywhere near it - keep all the stores together instead.)

Even better is if the store area is right off the freeway so most of the time it's on the way to/from the commute. And if not, it's quick to get to.

Sprawl does not mean a spread-out, rural area. Rural areas don't really have traffic problems in the way that metro areas do. Even suburbs of small cities don't have traffic problems on the same scale as major cities like NY, Atlanta, DC, LA, and Chicago. Traffic problems happen in dense, economically active areas. You have hundreds of thousands of people trying to move through the region every single day and that is what leads to the traffic jams. Sure, Kansas City is pleasantly spread out. Driving and parking there is very easy. But KC is also very small compared to most of the metro areas with serious traffic problems.

Incidentally, food and grocery selection in the city where I live is vastly superior. Within a half-mile I have Trader Joes, Whole Foods and a standard supermarket (which caters to a much more diverse population to begin with) in addition to a number of specialty and ethnic markets. There's a farmer's market every Saturday right down the street.

Also in close walking distance: Best Buy, REI, Bed Bath & Beyond, Blick Art Supplies, several bicycle shops. There's even a store that sells vinyl records.

I walk to work. I have a car. I use it for groceries sometimes but not often. I never have a problem finding parking at the supermarket or at home. (parking anywhere else is dicey, though)

Were you arguing with me, or helping me make my point? Because I agree with what you wrote - that's my experience as well. (And where you live sounds just like where I live.)

Neither, really. Though I might not have been clear-- I live in a densely populated area where there's public transit and I don't use a car much. I grew up in rural areas where the spread-out method works better.

What doesn't work is trying to solve traffic problems by spreading everything out. In places that already are spread out, there really isn't a traffic problem to solve and communities can decide whether they want mixed-use environments or segregated environments based on other factors. In places where you already have a critical density (like Eastern MA where I live), spreading things out is no more feasible than a subway in rural Ohio. Right now, trying to drive from Cambridge to Waltham at 6:00pm will probably take 45-60 minutes due to traffic congestion. That's because of all the people trying to leave Boston for the suburbs.

If I need a car for a short time period like shopping, I can rent one short-term - there's a car club parking spot about 2 minutes walk from my house, and costs about 5.50 GBP per hour, including fuel - or I could take a taxi. Of the people (i.e. mothers) I know who have done this, they've always taken taxis, to and from the supermarket, once a week. If shopping is the primary justification for having a car, the cost doesn't outweigh the alternatives.

I find spaced out living not conducive to walking from one shop to another, to a cafe to meet with friends, to a theatre or cinema, to a restaurant, to a pub; without limitation on alcohol consumption etc. A centralized shopping centre already exists - it's called the town centre.

I personally prefer to keep well away from freeways, motorways and their ilk. They're loud, ugly and mind-crushingly boring to drive on. I also think they scar the social landscape in a particularly unpleasant way - they tend to separate communities on either side, almost like rivers.

It's clear that our preference functions are very different. Mine is probably largely coloured by having grown up in a very walkable town in the west of Ireland (Galway), and now living in London; and having been horrified by the way most US cities are put together (i.e. apart from places like NYC and SF).

Driving around the upstate NY / PA area very clearly brought home to me how much I'd hate to live there, and driving around silicon valley on the 101, 280, 85 etc. was much worse, reminiscent mostly of a massive industrial estate. The only two places I've seen that I'd seriously consider in the US would be the aforementioned SF and NYC, and perhaps Boston.

But I do however have a vehicle - two actually: a scooter and a motorbike. In London, I enjoy negotiating (i.e. filtering or lane-spltting) the traffic - I rather prefer busy streets to empty ones, and anything is better than a motorway.

> It's clear that our preference functions are very different.

No kidding. I can't think of a place I'd rather not live in more than NY, with Boston taking second place.

A town center is not a replacement for a centralized shopping area. Town centers usually have high rents, so the stores are small and/or overpriced. They have their purpose, but they are not a replacement.

> having been horrified by the way most US cities are put together

And I like it, and am horrified by places like London and NY. I'm glad the US is big enough that there is room for all types.

Sprawl works well to reduce traffic only if the sprawl develops well enough so there's no real reason for people to travel between regions regularly. Otherwise, it'll most definitely increase traffic. Why wouldn't it? Increasingly large population spread over an increasingly large area, with all the traffic only going in a few specific directions.

If the sprawl is designed properly there are a large number of small roads connecting the regions, so the transit traffic is also spread out.

Sprawl reduces traffic only along the leaves of the commuting graph: few people live there, and no one commutes through the leaves to reach inner hubs. When a node stops being a leaf, more and more vehicles travel through it, which means increased congestion. It also means that people living on leaf nodes but who work in the hubs have to travel farther and farther, along more invreasingly congested nodes, than they do in their own remote neighborhoods.

This is certainly the case in areas like New York (whose suburbs grew largely because Robert Moses liked cars more than trains, although he himself did not even drive) and San Francisco (which has a unique bi-directional commute traffic jam problem, where both the city and far-flung suburban sprawl nodes are job hubs). I don't have a link handy, but I believe the growth of Atlanta followed this exact pattern and became a classic case study of awful urban planning.

This sounds counterintuitive but is absolutely true. I know that London instituted a "tax" on all vehicles entering the downtown area, which helped greatly with the congestion. When I was visiting Munich I also saw that some roads were deliberately narrowed to discourage people driving.

The infrastructure increase can never match the increase in number of vehicles. One can conjecture a modified version of Peter Principle: (Unless drastic measures are taken) traffic density will always increase to the level of congestion. Or think about the fact that regardless of how big your hard disk is, the rate it's being filled is generally constant.

So, bigger roads doesn't make too much sense (there are also arguments from landscape beauty, i.e. remember how they demolished the Beijing Old Town for easier access, more roads mean more of that.)

I wonder if the gridded road construction of Manhattan, with almost all roads about the same size, (save the Avenues), is a solution. Instead of a few big roads, build many smaller roads, which will then allow for efficient travel to many places.

The problem here is that the number of intersections scales quadratically, as the square of the number of roads. Each intersection cuts the capacity of the roads and represents a potential cause of gridlock and accidents.

"I think this is an interesting direction, though I wonder to what extent the real problem in urban planning is not having the resources—money—to do anything about it," says Sam Madden, an associate professor at the MIT Computer Science and Artificial Intelligence Laboratory who studies wireless sensor networks, including GPS units.

Resources-- and political will. It doesn't matter what your data shows if the residents won't let you build roads through their neighborhoods. In Cambridge, MA there are roads that actually already exist but rush hour traffic is deliberately blocked from using them. (eg Whitemore ave / Seagrave Road between Alewife Brook Parkway and Mass Ave)

It's like that thread about the guy who ran simulations to figure out the optimal way to board planes. Even if it's true, not gonna happen, 1st class pay partly for the right to board first. Exactly the same type of situation.

First class can still board before the rest of us in steerage in that case though.

First class on in what-ever order is most efficient for that part of the cabin, then the rest on in what-ever order is best for those areas.

Though what would really happen would be "first class on in what-ever order they fight for amongst themselves because they all consider themselves too important to listen to instructions from the boarding staff" followed by "the rest on in what-ever order they fight out as they don't care about the common good if that means they are on 12th instead of 1st".

Sometimes it takes a bold move in order to convince your customers about change. See: news feed, box wine, and nearly every apple product.

In fact, I've never figured out why first class has to board first. When I rode on Cathay Pacific on business, the attendants come get you from the traveler's lounge last, once everyone else has boarded. You don't need to jockey for overhead luggage space, so why wait longer in the cramped confines of the cabin? I wish more airlines did that.

I was looking for a conclusion, but couldn't seem to find it. Anyone? The closest thing I can find is that going from A to C clogs up B, so city planners should create a direct A to C route.

The clever bit is that they are using taxi routes to predict traffic patterns rather than just looking at where the traffic jams happen. They've demonstrated that creating direct routes which correspond to taxi routes does much to alleviate congestion.

The research itself could be interesting, but the article is terribly written and ridiculously dumbed down; I imagine the interesting parts have to do with the identification and partitioning of areas and routes. Shame about the article.

Traffic is the result of incorrect pricing. Its cheap to drive relative to the alternatives taking into account all non-tangible benefits like privacy and comfort or the lack of a schedule and predefined route. If it is more expensive to drive people will drive less. You can use good pricing to influence behavior. If you charged everyone getting on an Los Angeles metro area freeway $5 between 7-9am and 2-5pm Monday-Friday some people wouldnt use the freeways. Yes now they are tollways but they are already tollways only funded through taxes. Really this wouldnt be a great idea because most people will just drive on the streets resulting in a shift in traffic but probably not a significant decline in total traffic. To be more effective this need to be combined with a robust mass transit network. When gasoline prices spiked in California people started driving less but overall there wasnt a significant change in demand mainly because of the lack of viable substitute.

What needs to happen is a combined approach of dynamic pricing of driving and public transit along with investment in the transportation system as a system and good urban planning. Without a combined approach problems appear intractable but only because the incentives just are misaligned.

The problem in Beijing is painfully obvious if you've ever experienced the traffic jams there. The main cause of the jams other than cars is badly designed on-ramps and off-ramps onto the ring roads.

Beijing has a very unique on-ramp/off-ramp solution that I have yet to encounter in any other city. When they were first designed and put into use they made a lot of sense. A friend of mine who has lived in the city since 1999, said that back in the day there were almost no cars on the road and huge avenues. The on-ramps and off-ramps were designed and put into place at around this time.

The problem with the ramps is the the on-ramp leads onto the ring road and about 100m later there is an off-ramp. Once the traffic gets really bad the exiting traffic blocks the flow of the entering traffic. Once that happens the entire city comes to a stop because this on-ramp/off-ramp problem cascades throughout the city and everywhere becomes blocked.

That sounds like a cloverleaf interchange... Once a very popular choice to build because it only requires building one bridge, now less common because of that problem and because they use land very inefficiently.

Speaking of cabs in Beijing: how come I can never get one? I see empty cabs drive by constantly (and not just foreigners, locals too). Or they sit around not wanting to pickup fares. The whole cab system seemed broken when they didn't want to drive people places. Anyone have any idea what sort of incentive system these guys have or try and explain this behavior?

Single page printable version:

http://www.technologyreview.com/printer_friendly_article.asp...

Combine with OnStar's ubiquitous capture of private car driving, and maybe we already have the data in America?

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