[sustran] Fwd: Network issue Thinking Outside the Bus

bruun at seas.upenn.edu bruun at seas.upenn.edu
Tue Jun 5 21:02:35 JST 2012



Hello again everyone:

Pleas+e see the second half of the attached chapter Route and Network   
Analysis. It is entitled "Interaction between Route and Network   
Design". In it, I summarize Young-Jae Lee's 1998 dissertation. It   
takes into account three basic types of input:

Demand -- high or low
Travel speed -- high or low
Transfer Penalty  -- high or low

Then, it creates three possible different types of network, depending   
upon social cost, which includes a combination of operating cost and   
user time cost:

Transfer-oriented
Transfer-avoidance
Directly - connected

I consider it to really be quite helpful in understanding the route   
planning dilemma. A lot of the arguments that people have are really   
just a result of unstated assumptions. One person visualizes   
Burlington, Vermont (a city of 100,000 people in the US) others   
visualize Kolkata. The answer is different for both.

Eric

Quoting Paul Barter <paulbarter at reinventingtransport.org>:

> Thanks Karl for the thoughtful comments and Guangzhou examples. Gives me a
> chance to clarify a little.
>
> I don't think we will agree but it is worthwhile getting to a better
> understanding of where the disagreements might be. In that spirit, here
> goes.
>
> I'll make a few comments amongst your text below but here are two key
> points:
>
> -  Connective networks are not the answer to every problem or situation. I
> am claiming the idea often deserves more consideration. I am not saying
> that every city must make its network more connective no matter what.
>
> -  The point is to get to a "turn-up-and-go" level of service on more lines
> to make public transport more attractive overall. If your service
> frequencies are currently poor and you have a complex network with lots of
> overlapping services, then reorganising towards a more "connective network"
> (with fewer route kms) can usually help.
>
> - A key empirical issue here is the question of how much high frequency
> service matters. Those who are more sympathetic to connective networks tend
> to see the evidence as demonstrating that short headways matter a lot to
> the attractiveness of public transport.
>
> On 4 June 2012 17:31, Karl Fjellstrom <kfjellstrom at gmail.com> wrote:
>
>> To me there seems to be a contradiction between objectives of maximizing
>> transit ridership and saving passenger time, and many of the people writing
>> books and reports about transit, especially the ones who laud 'transfers'
>> as if they are something actually good.
>>
>
> PB: You are correct of course that connections are only a means to an end.
> I haven't heard of anyone saying they are a good thing except in order to
> get something else which is very good:  namely, high frequencies/short
> headways which give people the freedom to "turn up and go" at stops (and
> which fortunately also reduces the pain of waiting for those connections).
>
> But the key point is that sometimes reforms that increase the number of
> transfers does increase ridership by helping to increase frequencies.
> Minimising transfers will not maximise ridership if it means low levels of
> service on each line.
>
>
>> Some people making this argument presumably come from a fixed-rail network
>> background, and/or are promoting fixed rail systems, which perhaps helps
>> explain why they try to impose this fixed rail network thinking on buses.
>>
>
> PB: Interesting. Yes, there may be some correlation. Obviously, if you are
> a die-hard rail advocate you will certainly want to reorganise buses around
> the rail spines.
>
> But that doesn't mean everyone who is sympathetic to connective networks is
> die-hard pro-metro! I am not. And ironically, Jarrett Walker is often
> accused in the US of being pro-bus and anti-rail.
>
>
>> We saw this argument presented a lot in Guangzhou. People saying Guangzhou
>> doesn't have enough transfers, and has too many overlapping bus routes, so
>> we need to build transfer hubs and cut the bus routes so we can have more
>> transfers. To me it is a lot like arguing that Guangzhou's food is too
>> delicious, so we need to cut it back, make it less tasty so it's closer to
>> the average. Anyway, these consultant proposals, which culminated in a
>> transport master plan in 2006 funded by a World Bank loan recommending
>> dozens of transfer hubs and cutting the bus routes accordingly, are usually
>> thankfully and rightly dismissed by the city. And then the Guangzhou BRT
>> opened in early 2010. The Guangzhou BRT is based on an opposite premise.
>> It's a direct-service model, the idea being to minimize transfers and
>> maximize ridership and passenger time savings.
>>
>
> PB: I don't know GZ well so I am guessing here, but:
>
> -  If most routes ALREADY have attractive headways throughout the day then
> there would be no headway-based argument to simplify the network.  Already
> the case across most of Guangzhou? If so, there would be no point creating
> more connections or a simpler network for their own sake.
>
> -  On the other hand, could it be that, even though all key corridors are
> served wonderfully by overlapping routes, many routes in outer areas may
> have low headways (eg more than 15 or 20 minutes)? If that were the case,
> there might be some merit to some shift in the direction of a connective
> network. (Not necessarily any extreme change -- it is a spectrum of
> course).
>
> -  In addition, in dense cities like Guangzhou there is another common
> argument for reorganisation of bus lines (mentioned by Eric Bruun the other
> day): bus congestion on the busiest corridors with the overlapping routes.
> I guess Guangzhou's amazing open BRT has now shown a new answer to this
> problem.  But until the GZ BRT, consultants probably assumed that a shift
> to closed BRT or to rail would be necessary to cope with a corridor like
> that (which would force more connections). Maybe the consultants you
> mentioned were thinking along those lines. An honest mistake based on prior
> experience but now in need of updating in light of the GZ experience?
>
>
>> I took a quick look at the first link you provide below.
>> http://www.humantransit.org/2009/04/why-transferring-is-good-for-you-and-good-for-your-city.html.
>> The travel time argument is key, but the longer travel times are clearly
>> not the only disadvantage of transfers.
>>
>
> PB: Just to be clear, despite his attention-seeking headline, he is not
> really arguing transfers are good in themselves. But he is saying that if
> the network simplification can achieve high enough frequencies for the same
> input of resources, then you can actually get shorter total travel times,
> despite the need for the connections.
>
>
>> The analysis is wrong, for several reason, and I'm surprised that you are
>> promoting this material. When looking at frequencies and hence waiting
>> times, it assumes no overlap between the direct-service routes. The reality
>> is with direct service routes that you end up with a lot of route overlap
>> at key, high demand points. This provides many passengers - especially at
>> the high demand areas where they are most useful - with multiple route
>> options, at high frequencies. Secondly, the analysis assumes a 5 minute
>> transfer cost, which is far too low. Even in the best transfer situation
>> you should probably assume a 10 minute delay. And that is in the best
>> situation, e.g. where you just need to cross a platform. In other transfer
>> situations you may e.g. need to alight, cross a road, and walk to another
>> bus stop or platform, which could easily already exceed the 5 minutes
>> transfer time that the analysis lists. Plus you may need to pay again, and
>> you are uncertain about the waiting time. Plus perhaps the next bus is
>> full, or there is no seat on the next bus, etc.
>>
>
> PB: Yes he glosses over lots of these issues in order to make his key point
> via an oversimplified example. There is no denying that making a connection
> can be painful and we should only increase connections in a network if the
> payoff is worthwhile. It is one step in a wider argument that such reforms
> can often offer more attractive public transport, despite the problems with
> connections and the difficulties with making them easy enough.
>
> We should only reform towards a more connective network arrangement in
> cases where this really delivers better service not worse. An empirical
> question for specific cases.
>
> For example, if you already have very good frequencies without reforming
> your network (as in GZ?), then making it more connective may very well be
> pain without gain. I don't blame you for being sceptical in such a
> situation.
>
> Plus, in order to access some transfer facility, vehicles typically have to
>> do some additional manoeuvring, which adds to trip time and hence fleet
>> requirements and system costs.
>>
>
> PB: Agreed. And in hubs-and-spokes type networks the interchanges can also
> become bottlenecks for buses. Some of Singapore's interchanges have reached
> this point I think. You wouldn't want to over do it.
>
> But don't forget other kinds of connective networks, such as the simple
> grid, for which these transfer-point problems are less of an issue. But a
> grid raises other issues like how to get the bus stops close enough to the
> intersections without screwing them up. Singapore's bus stops are 150m or
> more from intersections: hence no grid of bus routes here. Lots of
> trade-offs, no free lunches ... Didn't mean to imply that network planning
> is easy.
>
>
>> Plus there's the cost of building and operating the transfer
>> facilities. It's why you almost always see when looking at fare levels that
>> what you misleadingly call 'connective' networks have higher fare levels
>> than the 'direct-service' networks.
>>
>
> PB: Fair point. Shouldn't ignore such costs if comparing the options. They
> should be counted when asking if the changes are worthwhile on balance or
> not worthwhile.
>
> It's typically disingenuous of people advocating transfers to gloss over
>> these issues of the actual physical transfer requirements and time and
>> other costs of transfers.
>>
>
> PB: Maybe some do gloss over them in their zeal. That's a pity. But in my
> experience, people advocating this kind of reorganisation are sincerely
> aiming for the benefits that flow from short-headway service. They
> genuinely want public transport to improve to attract more users. They are
> generally transit advocates. They are generally acutely aware that
> transfers are still a pain and that they need to be made as painless as
> possible. But if not, then yes, they are not being honest about the tricky
> trade-off to be faced here.
>
> The key point is to see that there is a trade-off between frequency and
> connections. And it runs both ways. If a city can't support frequent
> service on a 'direct network' that aims to minimise connections, then it
> will either have abysmal frequencies or require heroic levels of subsidy.
> In such a city, more transfers may be a price worth paying to get the
> frequencies up to a level that makes public transport more attractive for
> more people.
>
>
>> And misusing the word 'integration' as a way of describing proposals to
>> cut bus routes and connect them with other routes at hubs is one of the
>> reasons the term 'integration' now has so little actual meaning. Similarly,
>> calling these cut-up bus networks imposing high transfer costs 'connective'
>> is just another piece of doublespeak.
>>
>
> PB: I agree that integration has too many different meanings now, which
> causes confusion.
>
> Maybe you have seen some inappropriate proposals for bus reorganisation
> that are giving the idea of connective networks a bad name.  If such a
> proposal imposes high transfer costs without large benefits in terms of
> headways and strenuous efforts to make the transfers less painful, then,
> yes, it would probably be a bad idea.
>
> I don't see why 'connective network' is double-speak. If anything, doesn't
> it honestly acknowledge that the approach involves more connections in the
> network?
>
> Maybe the problem with the term is that it doesn't make the hoped-for
> benefit obvious enough! So perhaps the proponents should talk about
> "high-frequency connective networks" to highlight that the point is to get
> better frequencies. (Remember, no point doing it if you already have high
> frequencies)
>
> Hope this helps.
>
> Paul
> --
> Working to make urban transport and parking enrich our lives more and harm
> us all less.
> paulbarter at reinventingtransport.org
> http://www.reinventingtransport.org  http://www.reinventingparking.org
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