Access or Traffic Death

A new research paper from Florida Atlantic University discussing the foundations for 15 minute cities found that employment density is the highest driver of local travel. If people can meet their needs locally, they won’t travel outside of the neighborhood as often. This is important for a few reasons including some you might not expect. If people stay local to access destinations, it might mean less conflicts with high speed cars.

In transportation we often think about the mode of travel or conveyance, but if you consider access, the end destination is what most people find important. And that determines their travel choices as well as safety risks.

I’m often bothered that we think of our transportation systems as something that goes through places rather than to them. The place or end destination IS important. As Professor Jonathan Levine noted to us on the podcast in discussion with Greg Shill about a paper they co-authored,

“Accessibility” brings proximity into the equation. So mobility-based planning gauges the quality of transportation strictly on how easily one can move to a destination. But the problem is that’s a poor metric for indicating how well one can reach one’s destinations because you can have high accessibility even if you can’t move very fast, if your proximity is high, if your destinations are close or alternatively your destinations can be far away and you can move fast, but you still have low accessibility. So it’s really only accessibility that gauges the value of the transportation and land use system to people.”

Priority transit serving high job density destinations serves the best of both worlds. Not only can it go fast, but if designed correctly by serving destinations it retains a high level of access. When Denver’s RTD decided to run a light rail line around a hospital instead of through it, transit advocates groaned with dismay.

This is something we’ve been considering a long time and some of my early work was focused on the connections between destination employment and transit ridership. In 2009 I co-authored a TRB conference paper that was entitled Destinations Matter which linked high ridership light rail lines to employment along the route. It borrowed heavily from Pushkarev and Zupan‘s work on the subject but also data collection we did at the time.

A report a few years later, TCRP 167, found that transit ridership on fixed guideway rail lines was the result of the interaction between job/population density, CBD parking costs, and grade separation. Jobs was a high second predictor to this mix of factors which is interesting because it still tells us how important they are to people’s accessibility.

These days we focus so much on housing density and construction around transit, as we should, but sometimes it feels like it can be at the expense of the discussion about employment and destinations, particularly neighborhood serving ones accessible by walking, biking, and other mobility devices.

But there’s another angle to consider here on the other side of the land use coin. In low density car dependent areas where destinations are located based on car oriented planning, the placement of buildings like grocery or convenience stores can lead to more conflicts between vulnerable road users and cars.

We’re going to release a podcast soon with (also FAU professor) Eric Dumbaugh discussing the topic of vulnerable road user safety that considers destinations and land use based on his recent JAPA paper.  It’s a bit counterintuitive based on current practice but makes a lot of sense when you step back and think about it. The siting and location of grocery stores and gas stations and big box stores where people want to go are often along major arterials. This siting induces people to cross streets and leads to more traffic deaths.

So in a world where we are considering accessibility for the transportation system as a whole, land use decisions, specifically the location of destinations hold a more important role than perhaps we realize. Both in creating dense walkable neighborhoods that provide more destinations and realizing how the siting of destinations in suburban spaces influences access.

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