Accessibility Vs. Mobility Redux

Samuel Staley's picture

I'm going to riff off a recent Interchange Blog post by Michael Lewyn on the relationship between mobility and accessibility. Given the positive comments from the planning community to Michael's post, a little engagement may be necessary for both clarity as well as fully understanding the implications of reading too much into the accessibility versus mobility debate.

Michael makes a welcome attempt to clarify the distinction between the two terms, but I think he's incorrect when he concludes his post, after criticizing planning in "auto-dependent" suburbs: "It logically follows that mobility for all is highest in places that accommodate pedestrians, transit users, and bicyclists as well as drivers- in other words, that accessibility is mobility." As the author of two books on transportation policy, and one titled Mobility First, I'll beg to dissent-somewhat.

For the record, I agree completely with the observation that the terms "mobility" and "accessibility" are confused in the planning discourse, with the term mobility often incorrectly tied to automobile travel as if mobility should be dismissed or reduced.  This is unfortunate.

Mobility, as Michael correctly notes, is about moving people and goods from place-to-place. Higher mobility is good for society and cities (as I discuss in Chapter 3 of Mobility First.) Accessibility is something that is easily approached, entered, obtainable, or attained. Greater accessibility is also good for society and cities. Achieving one doesn't necessarily imply giving up the other. The two terms should not be conflated, in either common usage or in urban planning discourse. Mobility provides access, but it is not access. Also, accessibility does not provide mobility.

The automobile, in contrast, is a transportation technology, a method for obtaining things people desire. Cars are, in this respect, no different from busses, taxis, bicycles, or even our feet in the context of mobility (and more broadly accessibility).  Each of these technologies has functional advantages and disadvantages. The choice, and even preference for, one transportation technology over another is driven by the desire for mobility and its ability to provide as a means for accessing the goods and services we want.

Unfortunately, by conflating mobility, accessibility and transportation modes, we leave out the crucial discussion of the trade offs implied by consciously shifting from one transportation mode to another. Simply adding transportation modes to an existing built environment will not necessarily increase mobility or accessibility. If the buses run empty, and bicycle paths go unused, the provision of these alternative modes provides neither greater mobility nor greater access. Indeed, by shifting resources from more productive public investments, including greater capacity for the modes that make sense, overall accessibility may decline.

Thus, in the ongoing discussion in the planning profession about mobility and accessibility, a crucial question is what transportation modes need to be in what places and at what times in the neighborhood development cycle. Not all modes are created, or function, equally. Putting the wrong modes in the wrong place may compromise the healthy development of communities.

Sam Staley is Associate Director of the DeVoe L. Moore Center at Florida State University in Tallahassee.



Is mobility always good?

I don't see how it is always true that "higher mobility is good for society and cities." Suppose an imaginary parallel world where the same trips are made as they are in the contemporary world, except that each person is required to spin around in circles for ten minutes before arriving at the destination. This world would have more mobility (the additional spinning movement), but we'd hardly say this is an improvement. Wasted time, loss of production, higher risk of accidents, more pollution, etc.

The ultimate goal of the transportation system ought to be access: allowing people to reach the destinations they choose as efficiently as possible (while minimizing external impacts). This can be achieved either through granting mobility, by whatever mode is most appropriate for the particular case, or by reducing the distance between desired destinations. With the small exception of traveling for the enjoyment of traveling, mobility is only a means to an end.

Words and meaning among professionals.

When we discuss issues as professionals, it's only practical to have a language that we all understand. Some words have specific conceptual meanings that allow us to communicate without constantly re-explaining the fundamental concepts of our work. Yes, we need to be conscious of how our lingo presents barriers in other situations, such as communicating our work to the broader public, but that's a separate discussion.

The meanings of access and mobility are fundamental to transportation. What you described as access, "allowing people to reach the destinations they choose as efficiently as possible" is achieved through a balanced (ideally) combination of access and mobility. You essentially described mobility as movement without purpose (spinning around in circles), but that isn't the transportation definition. So how about a simple example?

Let's say you're making a commute trip to work by bus. You step out of your home and walk 1/2 block to a bus stop where you wait to board a bus with arrivals at 10 minute headways. During this part of your trip, you'd be experiencing a fairly high degree of access to transit relative to your individual trip. Once you've boarded the bus and begin traveling, you're experiencing mobility. If you're traveling through a dense urban area, with very frequent stops and high ridership, then mobility is just so-so, but accessibility is high for that route. Let's say, instead, you're lucky enough to have the option of a second route at the stop in front of your home and it's an express route. First, your access to transit is greater because you have two routes to choose from, and second, your mobility on the express route would be greater because it makes fewer stops along the way--getting you to your destination more efficiently.

Hopefully you see a key relationship here between access and mobility: increased access tends to reduce mobility because it adds travel delay. Or, you could say the opposite: high mobility requires limited access.

So, is mobility always good? That's a tough question from the high-level, societal perspective because it has obvious social, environmental, and economic implications. The more relevant answer to your question is that mobility is necessary for life as we know it. We should all be knowledgeable about the language of our work so we can get on with working together to help our communities balance those implications of modern life.

Two versions of access?

This seems to be a worthwhile conversation to have. We agree that mobility just means movement (I don't think it has to be unnecessary at all), but it looks like there are two slightly different versions of "access" being used. I think you are using access in terms of having access between the transportation system and the adjoining land uses, which is how it's used in access management.You are saying "access to transportation," essentially. If I understand correctly.

Others also use access more broadly, as in having access to the places you want to go, by means of the transportation system. Here's an example of it being used this way. See Charles comment above too. Staley appears to define access broadly in this post: "easily approached, entered, obtainable, or attained," so that's why I was running with this. The pharmacy, for example, is "easily approached" by me if I have a means of traversing the distance between my origin and destination without an unreasonable cost to me. This question is mode and distance neutral, really.

I'm not sure it's a bad thing that access is used both narrowly and broadly, but it obviously requires some context and explanation.

Correct link

Sorry, here's the correct link for one a take on "distinguishing between mobility and accessibility."

Good Definition of Access

Good point. I meant "access to places," which can be accomplished either through mobility or through proximity. I have equally convenient access to a store 1) if I live 3 miles from the store and can drive there in 5 minutes or 2) if I live a block from the store and can walk there in 5 minutes.

"We agree that mobility just means movement (I don't think it has to be unnecessary at all)"

Agreed. Mobility can be necessary and desirable. I am certainly glad that I can get to places that are not near where I live.

But I think it is a mistake to say that more mobility is necessarily better, as Staley says: "Higher mobility is good for society and cities (as I discuss in Chapter 3 of Mobility First.)" Americans today spend too much time driving back and forth among distant places that should be located closer to each other for more convenient access with less mobility.

Maybe we can convince him to write a new book called "Access By Proximity First, Mobility Second."

Charles Siegel

Mobility not just ability to drive

The way I've always understood mobility and access terminology (from a Planner's perspective) is the way Jeff has described above. It seems that you are using the term mobility to soley describe the ability to drive a car. While road investments may or may not increase mobility for drivers (e.g. your proximity as a zero sum game example), they do not usually increase mobility for non-drivers. When people like Staley talk about "mobility", they are really talking about "drivability".

Mobility Is Ability To Move Around

No, I am using the term mobility to mean the ability to move around, not just the ability to drive.

If I live in sprawl with very high speed commuter rail, I might commute one hour and travel 70 miles by rail. Then I have as much mobility as someone who commutes one hour and travels 70 miles by car.

If I live in a more compact city, then I might commute one-half hour and travel only 10 miles. Whether I commute that ten miles by car or by rail, I have less mobility but better access than the person who lives in sprawl.

Charles Siegel

This is a wonderful discussion

Maybe to further it using Staley's own words from elsewhere: "Great urban places come first because their benefits offset the individual and social costs of greater dependence on a less flexible, restricted mode of transportation. In the end, higher transit use is an outcome, not an input, in economic development and urban redevelopment. Federal and state policies should emphasize transit in the sense that it becomes a service that local residents and businesses demand." While the effects of mixed-use developments may not be immediately felt, in a couple of generations it will be, just like it took pro-road/autocentric partisans a couplathree generations for their myth to be firmly inculcated. The arguments used by those who argue against our broadening our modality? Could be applied to roads at the Interstate inception in the mid-50s.

David Parvo
Most Senior Fellow
The Placemaking Institute

There needs to be some way to say this

I'm not wedded to using the term accessibility broadly, but there ought to be some way to convey the overarching purpose of connecting users of the transportation system to their their choice of destination - maybe "trip completion" would work. Just using the two poles of accessibility (narrow) and mobility misses a crucial land use component that is every bit as important, and it makes auto-dependent low-density development seem preferable to compact development.

Consider the typical rural trip: Most folks have a private vehicle in the garage and the destination has a parking lot right in front with plenty of spaces - high points for accessibility to transportation. The drive is relatively fast with little congestion - high points for mobility. Given these two criteria alone, we'd probably want to ruralize everywhere. But when proximity is factored in, the equation shifts considerably. Urban areas may have lower levels of access to transportation (even if the modal options are greater, they typically are less convenient than just hopping in the car in your garage), and decreased mobility due to congestion. But this is offset by the compact nature of the land use. You don't have to travel as far.

Staley thinks more mobility is always better because he is not adequately figuring land use into the equation. He is treating the choice of destination as a fixed, external variable when it really isn't. There needs to be a broader way of framing this.

Two Types Of Accessibility

"high points for accessibility to transportation."

I think you got one term right there. I would say that, when we need to be more precise, we could use the terms:

- accessibility to transportation.

- accessibility to destinations.

Using your examples, the people who live in a rural area have high accessibility to transportation but only moderate accessibility to destinations.

The people who live in the city have high accessibility to destinations but only moderate accessibility to transportation (if their city does not have excellent transit).

Staley does not think about accessibility to destinations.

Charles Siegel

That sounds right

Charles, I think you've put your finger on the difference.

I looked up the definition of accessibility in a textbook, Geography of Urban Transportation:

"Accessibility refers to the number of opportunities, also called "activity sites," available within a certain distance or travel time."

This is from Susan Hanson, a geographer, but I know that the text is assigned to planners as well. She's using opportunities, which I think is what you mean by destinations.

To muddy the waters, planners also use accessibility as short-hand for something being accessible to a disabled person. You might say, "we've decided to make some accessibility improvements to our buses" by which it is understood that hydraulic lifts, etc. are being installed. In this case, the question "accessible by whom" would need to be clarified if the context did not do so.

Not News for Planners

Putting the wrong modes in the wrong place may compromise the healthy development of communities.

Mr. Staley’s central point is one that virtually every planner and urbanist is thorougly aware of. This goes back to Jacobs and Moses – diffusing to the rest of the United States shortly thereafter. There are countless examples of communities that have been “compromised” (the less reserved might say “ruined”) by the emphasis on private autos as the primary transportation mode – a major factor in the decline of American downtowns and main streets.

The type (or mode) of transportation infrastructure helps shape the built environment. A majority of planners (and the rest of Americans, as evidenced by real estate values) view “healthy” communities as places residents can walk or bike with conveniece and safety. Like the emphasis on the single occupancy car mode led to the transformation of many healthy communities to unhealthy ones, a greater emphasis on alternative modes will help restore those same communities.

Mobility, … is about moving people and goods from place-to-place.

Mr. Staley and other libertarian road-subsidy activists argue that car driving is a superior technology, as it allows one to travel farther, faster in many (uncongested) places. If the goals of mobility were this simple, they would be right in many cases; however, other community goals such as improving environmental and public health, efficiency of public services, and cost of living are affected by transportation mode. Bringing places physically closer together with a compact development pattern is a central purpose of Smart Growth because it furthers these goals. Mobility is improved by focusing on reducing the distances between places; Sprawl growth, by contrast, decreases mobility by pushing places further apart - resulting in an emphasis on increasing road and highway capacity in the hope that travel speed can make up the difference. Unfortunately, this planning approach, favored by libertarians, has exacted high costs on society that outweigh the benefit of increased mobility, as the term is defined by Mr. Staley.

Mobility And Access

I think the definitions of the two words are clear.

"Mobility ... is about moving people and goods from place-to-place" (as both Lewyn and Staley agree). The more movement of people and goods there is, the more mobility there is.

Access is about the ability to get to places you want to go, such as the places where you work and the places where you shop.

These definitions should make it very obvious that Staley is wrong to say say that greater mobility is necessarily better for society.

Imagine two cities that have the same layout except that WalkableCity is four times as dense as SprawlCity. People in SprawlCity travel twice the distance as people in WalkableCity to commute to work, to go to the store, or to get to other destinations. There is twice as much mobility in SprawlCity but equal access in SprawlCity and WalkableCity.

All else being equal, the people in SprawlCity are worse off: they have to spend twice as much on transportation as the people in WalkableCity with no extra benefit.

Anyone who claims that more mobility is necessarily good for society is blind to what has happened to American cities during the last 50 years, when mobility has increased dramatically (per capita VMT more than doubled) with huge costs and without significant benefits.

Charles Siegel

Good Points about Context of Access and Mobility

Would this be a meta-conversation? I love talking about how to talk probably more than planning to plan.

It's a good conversation; I realize that I was thinking in the somewhat narrow spectrum of transportation planning. Coming from engineering origins, I tend to think operationally, i.e. sometimes down in the details.

In my example, I referred to access at the origin of one's trip and of course I agree access is equally important at the destination as others have pointed out. It's also important between modes, segments of a trip, etc. Sometimes it's necessary to think at that level of detail, but in the bigger picture, if someone lacks access anywhere along the way, then I would say accessibility to their destination is the challenge.

On the the topic of valuing mobility, I didn't read Staley's piece as being auto-centric at first--he seemed to be making the case for context. It's a tricky question to ask if increased mobility is always good. For any fixed set of land use conditions, I can't see why it wouldn't be in our interest to improve mobility because it goes hand in hand with resource efficiency. However, as Charles noted, if the distance between places is very high we'd be better served to turn our attention to smarter land use and reduce total resource consumption first. My guess is that's when my agreement with anyone at the Reason Foundation would stop, but again--different discussion.

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