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Very interesting. I'm certainly looking forward to seeing the book as a whole!

I blogged a bit about mobility v accessibility back in April last year - in response to your earlier blog posts on the debate. In general, I felt (at least at that time) mobility was more of the "means to the ends" whereas accessibility is the ends.

Ultimately, we want accessibility. In some cases accessibility can be enhanced through better mobiilty, in other cases increasing mobility may reduce accessibility or accessibility may be improved in other ways (ie Manhattan has fantastic accessibility even if it it slowish to get around).



I'm with you on this one. I would even take it further and claim that mobility is more important for personal freedom than accessibility

Local accessibility is very nice - when you live in a good central neighborhood and rarely have to leave it... But for one to enjoy both the diversity and economies of scale created by cities - mobility is crucial. It's especially relevant to working in the best position for you in the Metro area without the need to compromise because it's more than 3 km away; and when your social circle goes beyond that radius.

I'm an Architect and do appreciate the greatness of accessible neighborhoods. However, normally those places are a symptom of working cities rather than a cause.

Tom West

If you have a city set up a certain way, then you have top increase mobility to increase access. However, if you deliver some significant improvement in mobility (e..g building a subway), then you can end up with an gradual improvement in access (through intensifcation), even though mobility remains at a constant (higher level).

So Access <-> Mobility seems to be a two-item loop.

David P

Thanks for posting on this, Jarrett - it's one of the aspects of transit planning that is misunderstood by many professionals in and the field. Your post does a good job of explaining it from the medium-term perspective of the transit planner, rather than the more widespread ultra-long-term views of the urban planner or the regional economist.

The Federal Transit Administration's guidelines for evaluating transit projects are centred on mobility (travel time improvements) for the exact reasons you outlined: the impacts of a project and eventual redevelopment is indirect, uncertain and difficult to quantify, whereas the mobility improvements are immediate and easily quantifiable.


A very interesting subject, and well addressed.



I think your point is insightful and very valid. Expecting agencies to pursue goals that are generally beyond their control is just a recipe for failure.

But I have to quibble with this sentence, "This map is, quite literally, a picture of your mobility."
By your initial definition of mobility (Litman's), a person's "mobility" would be increased if they had to take a circuitous route to get to the area shown on the map. But since the map also accounts for travel time, it is incorporating some of the aspects of "access".

You then redefine mobility in this sentence, "Mobility is how far you can go in a given time."

I think it's a valid redefinition. Your meaning is much more 'meaningful' than what you describe as Litman's usage. I'm not in the industry so I'm not sure how prevalent the various definitions are. But it seems to me that if you're going to redefine a term, you need to devote more than a sentence to doing so. It's not fair to dispute Litman's argument about which goal is more appropriate if you're going to change the definition of the terms mid-argument.

(I also wouldn't be so picky about terminology for a blog post...but you say this is for print. You won't get to rebut people's arguments until the paperback edition!)
(While I'm proof reading, you also have a typo in "It shows where you can go, in a give time, right now, in the city as it is.")

But, as always, I think you're going after very important concepts and I appreciate your willingness to bounce them off the blog first. :)


UPDATE: In response to MU's excellent comment, I've deleted the paragraph he refers to ("This map is, quite literally, a picture of your mobility.") That also eliminates the typo he found!

Multimodal Man

A critically important point! A few years into transit planning I recognized the point you are making but I couldn't articulate very well because I got stuck trying to frame it in passenger miles. A job well done. This should be a required intro for all transit planning course work.


As a lyperson, I think that transit service is simpy a means of conveyance from A to B.
The hours of operationa nd the frequency of service will depend on ridership demands and destinations on a case by case basis. That will of course change with development and changes in land use.

I don't think that you can apply a universal measure of mobility or access as a transit "goal" because of vastly different circumstances where transit service may be provided. i.e. buses can't climb steeply twisting roads in hilly communities, and certainly not economcally in sparely populated areas.
i.e. Depending on the circumstances, I think it's perfectly reasonable for a transit system to decide "you can't get there from here" (that it's not economical to provide a service), and that shouldn't be a black mark against the system (maybe riders are just being too demanding).


Good post! My thought is: talking about mobility and access as if they're separable is pretty difficult. People want access to activities - their functional reason to make a trip. And they need mobility to get there.

Obviously any measure of "mobility" that measures how far people travel as an indicator of quality of life is crazy. Sometimes what people want is a generic good they can get closer to home or over the internet. But other times it's access to the soccer field one's team is playing at, a family member or romantic interest across town, a particularly great deli, or a really great job that's hard to get to from a place where one can afford to live. In those cases, the ability to get where you want to get to, and when, does make a big difference in one's quality of life. I don't know how one comes up with a measure that's careful enough to distinguish between access that could be had closer to home or without a trip, vs. access to something very specific at a particular time and place.

I don't see how the two can be separated, is all I'm saying. People have a radius they can travel within, and most people feel their life is better if that radius is less constrained. That's inherently at odds with a societal interest in conserving travel. It's one of the reasons I'm in favor of pricing, because setting a price makes people consider whether the trip they're making is valuable enough to go the extra distance instead of accessing a generic activity closer to home.


Hi jarrett,

Love the discussion of conceptual issues. I feel you could benefit from experimenting with their presentation- after all, the book will sell to a wider audience than those who seek out the blog.
I think it could be useful to test the readability of separating the conceptual and descriptive content. I'd try 1. a soft, narrative scenario where we travel in the shoes of someone making these decisions, & 2. A concise treatment of the concepts in abstract terms.
Could be the blend style works better, but if this is the lynch pin of the book, I think the layperson (and even the jaded pro) want an easy way in.

Jack Horner

Very good.

Hope this doesn't seem like nitpicking, but it's worth distinguishing -
1. mobility: the ability to get around; more of of it means it is easier to get around; and
2. movement, which is the outcome of mobility plus desire; more of it means there is more travel per person.

Sometimes you use 1 to cover 2., which can be confusing. eg para 'so there are two problems...'

and 'three miles worth of mobility'

and para 'Defined this way...'

and para 'Transit that participates...'

The Litman quote at the start which is said to 'define mobility' does not actually do so very clearly, and it veers onto other issues which probably should be postponed and dealt with explicitly.

All the best with it.


Transit agencies already count passenger-trips, linked and unlinked--why not make it clear (in the book) when those statistics are more appropriate? Most transit agencies already understand this in their promotional literature--TriMet boasts of 100 million boardings per year, not X billion passenger miles--but the latter figure is used inappropriately, as you note.

One other issue, which you hint at here (and which you have tackled more directly in other threads, such as discussion of Prof. Condon's proposals for Vancouver BC's Broadway corridor), is the notion that mass transit is in fact in opposition to improved land use--that it only encourages things such as suburban-dwelling, long commute distances, etc. (essentially, that it promotes many of the same vices as do freeways, though certainly not all of them). You might address this forcefully in the book, if you haven't done so already.


The precise relationship between these two concepts is indeed quite murky and I'm glad you are taking on the challenge of sorting it out in your book. However, I think you have incorrectly limited the term accessibility to land-use effects. Accessibility is a function of both land-use AND mobility. Mobility is one of the mechanisms by which accessibility is calculated/created. The transit providers primary job is to provide greater access to destinations that riders want access to. The mechanism through which they do this is mobility, but access to destinations is still the goal.

I think you are onto something by using the map. This map is calculated based on the existing transit network. It shows all the geographic locations a rider originating at the point/time can get to. However, what really matters to the rider is what destinations are located within those zones. Of course, which destinations are valued is different from rider to rider. I like the map because it explicitly shows the mobility provided by the transit system. The accessibility is left to the rider to determine for themselves based on their own values/preferences. The short-term goal of the transit agency could be seen as providing the greatest access to destinations for the greatest number of riders while maintaining some minimum level of accessibility to key destinations for all riders. Of course, for a transit agency calculating accessibility is a much more complicated task because it requires that they understand which destinations their riders value and which ones they don't.

I also agree that from the perspective of the transit operator, land-use change is a secondary, long-term effect. However, if encouraging denser, more transit-friendly development is a long-term goal of the community, then some transit investments can support that goal. To me, this is an argument for better integration of transit operations with regional planning and with other aspects of city governance (economic development for example). If we restrict the goals of the transit operator to mobility for existing customers, then I think we may be missing an opportunity to link transit to other city/regional priorities. In some cases, a region might be willing to provide greater subsidizes for a transit investment they think will provide significantly greater long-term accessibility (through land-use change and real estate development) than an investment that only provides an incremental increase in accessibility because it doesn't drive a long-term land use change.

jack horner

Further miscellaneous subediting suggestions. These are general comments - I'm not suggesting you would do the things I'm advising against. I think your material is pretty good in terms of clear ideas and line of argument. For the record:

- Don't say 'commuters' (as many do) when you mean 'public transport riders'. 'Commute' should refer to the journey to work. Using it to refer to all public transport riders blurs the distinction between different market segments and subliminally encourages the undesirable view that handling commuters (work trips) is public transport's only significant task.

- Don't say (as many do) 'people' when you mean 'trips' - as in 'Sydney's trains carry 300 million people per year'. Public transport trips are composed of some people who use the service a lot, some who use it a little, and some who don't use it at all. Using 'people' to mean 'trips' blurs these distinctions.

- Use language that encourages the idea that we are all 'public transport riders' at some times for some purposes. Don't use language that encourages the idea that 'public transport riders' are a fixed subset of all people, like 'old age pensioners', for whom special provision must be made. Ditto for 'motorists', 'cyclists' and 'pedestrians' for that matter. The distinction is important to combat silly generalisations like 'people are in love with their cars' or 'people won't use public transport'.

I maintain that accuracy on what may seem like small points like these is important for the writer's clarity of thought and, cumulatively, for the reader's understanding. Often when you realise that you have used some keyword in a sloppy way, it then makes you realise that the whole idea of the paragraph or section must be unpicked and resewn.


This sounds like one of the vaguely interesting yet ultimately unproductive semantic debates that my grad student friends engage in all the time. The US -- and much of the rest of the English-speaking world -- is still not sold on the basic idea that living in the city is for anyone but young, single, childless people and they are busy building and moving to exurbs with walk scores of zero. Until that changes, this is just navel-gazing.

Being the stand-up bloke that I am, however, I will offer a compromise that should satisfy both sides in this "debate" in the hope that we can move on to something useful: the figure of merit for urban transit is the number of common destinations you can reach in a given amount of time using transit and walking; the "basic unit" is then "person-destination-miles per minute" or something like that.

Note that this merit function is different for urban vs. suburban transit (where urban is defined as where it is easy for people of all ages, with and without kids, to live without a car): the purpose of urban transit is to make the city highly livable without a car so that people will (mostly) give up their cars and move there and thus should be high-frequency all-day in and between urban areas.

People in the suburbs are simply not going to give up their cars, so attempting to provide them with an urban level of transit service is a pointless waste of money that could be better used in the city; so for those areas we should focus on reducing commuting VMT, which is much easier.

So now you can call your publisher and tell them you're going to write a book about why we should raise taxes on petrol and impose urban growth boundaries, both of which would do a million times more for transit and urbanism than this discussion.


I’m not implying that the others are unimportant, only that the first of these – improving access by improving mobility – is transit’s primary job, just as firefighting is the fire company’s primary job.

I think that this is the most important sentence in your post.

The analogy is crystal-clear. It's obvious to anyone that the best fire departments are the ones that can most quickly put out fires. But it's equally obvious that, given the choice, you'd always rather have fewer fires.

Of course, the analogy isn't perfect. Some people would prefer to have a 10-minute commute to a 0-minute commute, and some people ride trains (or drive cars, for that matter) just for fun. But as a first approximation, I think it's fair to say that, holding everything else constant, less travel time is better.


As a conceptual matter, access and mobility can be separated. But in the ways people think about them, it's no so easy. An actual example:

Residents in a poor Oakland neighborhood have limited access to grocery stores. They complain about their transit service, even though it's more frequent than many parts of town. They say it's not easy to take the bus to a grocery store, they often have to transfer, it takes a long time. They ask for a direct bus to grocery stores out of the neighborhood, even though that would disrupt the pattern of lines in the city (see Jarrett's previous posts on the need for connection).

They're not wrong, they have a real and serious problem. They look to the transit agency because they've gotten used to the idea of taking the bus to a grocery store.

But they're looking for a mobility solution to what is, IMHO, an access problem. People in more affluent Oakland neighborhoods don't need to take the bus to a grocery store. The grocery store is within walking distance (or in the Hills, a short drive). I'm a bus fan, but I don't want to have to routinely take the bus to reach the grocery store, and I don't.

A modest grocery store has opened within the neighborhood, the city is trying to bring in a bigger one. But it shows the difficulty of untangling these things.


One enormous elephant in the room here seems to be the notion of accounting for the costs/spending on transportation and utilization of integrated billing/pricing to leverage said outlays resulting in optimal use, performance and benefit AND notable should potentially be able to play a critical role in driving and organizing cooperative transport modes/services over single-owner/driver mode, which is not only highly wasteful, but inordinant costly and thus a BIG factor in pushing many, many individuals and households into functional poverty here in the US. Said more simply when will there be a single mobility management and membership service that makes the bargain of dramatically reducing individual/household transportation costs? After all it seems pretty compelling to me that virtually no one wants to spend more on transportation itself....

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