Is a walkable neighborhood always a healthy neighborhood?

In planning culture “walkable” or “bikeable” neighborhoods seem to be synonymous with healthy neighborhoods. The logic is straightforward: neighborhoods that promote walking and biking increase residents’ physical activity and that’s good for health. The research mostly backs this up; specifically, most studies find walkable neighborhoods have more active residents. (An interesting outlier is Minneapolis-St. Paul where residents’ in walkable neighborhoods replaced recreational activities with utilitarian travel but total physical activity remained mostly unchanged in this study). Walkable neighborhoods can potentially impact our communities in other positive ways (i.e., social, environmental, or economic impacts) however, for the purpose of this post I’ll focus on physical health.

We’re now starting to understand that physical activity from active travel is more elastic than leisure-time physical activity in relation to the built environment. That’s great news, planners can play a key role in increasing people’s physical activity; but, what about other aspects of health and active travel? Namely, shouldn’t we now turn our attention towards hazards cyclists’ and pedestrians’ are exposed to during travel? More importantly, shouldn’t we be making plans to mitigate those hazards?

A question that sticks in my mind: How do we move from only talking about walkability to including other aspects of healthy neighborhoods? For instance, how do we design cities that promote physical activity and protect against other hazards. Two examples I’ll discuss here are exposure to traffic-related air pollution and crashes with motor vehicles. To describe truly healthy neighborhoods we could come up with a much longer list – to name a few – access to quality foods, healthcare, and green space or exposure to noise or crime. Air pollution and crashes are interesting because in Minneapolis we may actually be close to mapping the risks. I’ll make the argument here that the first step towards measuring these risks is to understand patterns in bicycle and pedestrian traffic. We need to know where people walk and bike to estimate exposure (more on that later).

Example #1: Traffic-related air pollution. We know air pollution is bad for us. We also know physical activity is good for us. What we don’t know is how much of the physical activity benefit we get from walking or biking for transport is modified (i.e., canceled-out) if we walk or bike in polluted environments. It’s difficult to measure health impacts of any risk factor (usually this involves very large cohorts of participants over decade-scale time periods) and even more difficult to tease out nuanced interactions like this. What we are starting to get a handle on is what level of air pollution exposure is “typical” in different types of urban environments. Since emission sources (i.e., vehicles, homes, and businesses) are typically more concentrated in urban centers, walkable neighborhoods tend to have higher levels of air pollution. This seems to hold up in clean cities (Vancouver) as well as dirty cities (Los Angeles).

Not surprisingly, exposure seems to be associated with traffic and concentrations for certain pollutants can decrease rapidly as you move away from heavy traffic corridors. For example, some particulate air pollution measurements I collected last summer in Minneapolis (a more detailed post on this to come in the future!) suggest that by simply moving 1-block off major roads a person can significantly reduce their exposure. This seems like low-hanging fruit – modest shifts in the bicycle network (i.e., moving bicycle facilities 1-block off major roads) can yield meaningful reductions in air pollution exposure when cycling. The bad news, current Complete Streets legislation doesn’t allow for shifting funds to adjacent roadways.

Pictures of low and high pollution environements.

Where would you rather bike? These are pictures I took while measuring air pollution by bicycle last summer.

Example #2: Crashes with motor vehicles. Again, we know crashes are bad for health and physical activity is good. Earlier this year the good people at the City of Minneapolis bicycle and pedestrian office released the first map of bicyclist-motorist crashes in Minneapolis. This is a great step forward! Of course, there are some limitations; for example, we need to do a better job of estimating bike and pedestrian traffic to be more confident in going from accident counts to rates (more on that below) and we usually don’t have full information on all the accidents that occur (typically from hospital and police records). Improving those two data limitations will enable planners to better identify hot-spots for crashes.

Bicycle-motorist crash counts 2000-2010. Source: City of Minneapolis.

Bicycle-motorist crash counts 2000-2010. Source: City of Minneapolis.

Where do we start? First things first… start counting! The best thing we can do to understand exposure to these hazards is to determine where people bike and walk. Estimating biking and walking traffic with reasonable spatial precision will be the backbone of estimating exposures to other hazards. Implementing this type of traffic monitoring program is not new territory in the transportation field. We’ve counted and modeled motor vehicle traffic for decades. Conceptually, a bicycle and pedestrian traffic monitoring program would look very similar – set up a reference network that counts cyclists and pedestrians continuously and supplement that network with a relatively larger number of locations where counts are taken on a short-term basis (e.g., days or weeks). Luckily, Minneapolis has been relatively forward thinking in this area and StreetsMN reported on the first iteration of these types of programs earlier this year. A team at the University of Minnesota is field testing a traffic monitoring program for the off-street trail network in Minneapolis based on the principles developed for motor vehicles.

We have a unique opportunity. The Minneapolis-St Paul bicycle network (and to a certain degree the pedestrian environment) is in the midst of a relatively rapid build out. We have the chance to shape what that transportation network looks like – a rare chance indeed. Let’s make sure we’re not only focusing on density, walkscores, and bikescores but ensuring we take a comprehensive approach to designing truly clean, healthy places.


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6 Responses to Is a walkable neighborhood always a healthy neighborhood?

  1. Mike Hicks October 9, 2013 at 7:16 am #

    I wish Minneapolis and Saint Paul were better about upzoning parcels within a block or two of major corridors — I agree that it’s good to be able to move a short distance away from the heavier pollution (my own reason really has more to do with noise pollution though — I’ve always been a pretty light sleeper and otherwise noise-averse).

    But I know I’ve seen reports stating that bicyclists are healthier than expected — they often need to ride in traffic where pollution is very heavy, but the benefits of exercise outweigh the pollution. I’m not sure if the same holds true for pedestrians at all.

    A big issue is that many denser areas have poorer populations, and poverty tends to blow away everything else when it comes to health (as well as education, etc.).

  2. Cedar October 9, 2013 at 7:41 am #

    When I started to read this, I immediately thought of some of the neighborhoods in LA, neighborhoods that are very walkable and have good street life, yet struggle with high crime rates. I can’t think of any as extreme examples in the Twin Cities (although there are neighborhoods where people are nervous about walking around at night), but personal safety should certainly also be a consideration. If we want people to walk, they need to be feel physically safe from crime, among other hazards, while walking outside.

  3. Bill Lindeke
    Bill Lindeke October 9, 2013 at 11:53 am #

    I’m sure you’ve seen this study (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920084/) from thenetherlands and this one from CA (http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1295).

    Kind of a bummer to think about. How much does air pollution peak during rush hours and dissipate the rest of the time?

    • Steve Hankey
      Steve Hankey October 9, 2013 at 4:05 pm #

      Good point. The Netherlands study (and others) found that for an individual choosing to bike the physical activity benefit outweighs air pollution (unless you stop going to the gym after you start biking!). For a group of people it’s more complicated… not all people will change their behavior (i.e., walk more) if they move to a walkable neighborhood but everyone will be more exposed to air pollution. I think if we plan for this we can have walkable neighborhoods that are clean too. I’m going to write another post specifically on physical activity and air pollution in the next week or two.

      For your question, in general, concentrations are highest in the morning and decline over the course of the day (the reason: as the air warms emissions mix higher and higher in the atmosphere), but that can change based on local weather conditions.

  4. Walker Angell
    Walker Angell October 9, 2013 at 12:12 pm #

    “modest shifts in the bicycle network (i.e., moving bicycle facilities 1-block off major roads) can yield meaningful reductions in air pollution exposure when cycling.” Very true. However, that might in many cases also mean moving bicycling away from retail and other destinations, lower the value of active transportation, and so encourage more driving and less bicycling.

    Also, have you studied the future of auto pollution much? With hybrids, plug-in electric, and auto stop/start, all combined with people driving less, I wonder how significant motor vehicle pollution will be in the future. Is it reasonable to expect very significant decreases?

  5. Steve Hankey
    Steve Hankey October 9, 2013 at 4:20 pm #

    Re: the future of auto emissions. The short answer is I’m not sure we know. On a per vehicle mile basis it’s safe to assume emissions will go down (i.e., cars in the future will pollute less). But the general trend over decades is increasing vehicle miles traveled per person (we need to turn that around) and more dense city means more vehicle emissions in a smaller area… If we want clean, dense cities we absolutely need people to walk and bike more in my opinion.

    All this isn’t meant to trash walkability but instead make sure we are thinking about other consequences as we move forward. For example, I think about your comment regarding moving bike lanes off retail corridors frequently. I’m not sure what would happen. In any event its seems like Minneapolis is moving towards a bicycle network backbone that would be removed from traffic (see the bike master plan: eventually transitioning bike boulevards to greenways). I could see a compromise being implemented – make the backbone of the network trails/greenways and supplement that with bike lanes that provide access to retail. That way, bikers could spend the majority of their trip removed from traffic and ride near vehicles at the beginning/end of trips.