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Understanding the radius of demand for transit

Last week The National Post published an article talking about Toronto’s Crosstown LRT and how it’s spurring a wave of development all along Eglinton Avenue. Below is a map, taken from that article, showcasing some of the developments that are currently in the pipeline and awaiting the Crosstown’s opening date of 2020.

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Not surprisingly, developers like transit investment. But more specifically, they like fixed track transit investment. Rarely do new bus routes elicit the same sort of response that you’re seeing above. And that’s because fixed track investment has permanence. If you’re going to go long on an area, you want certainty.

As the Crosstown tunnel boring machines move across midtown Toronto, I thought it would be interesting to look at a transit concept that I first learned about through Jarrett Walker’s Human Transit blog. It’s called: the radius of demand

One of things that transportation planners look at when designing and building a new line is the spacing of stops. Typically, as you move from buses all the way up to subways, the spacing between stops and stations increases. Spacing is always a bit of a trade off though, because more stops means easier access for riders, but it also means slower overall service. Somewhat famously, Paris designed its metro system so that you’re rarely more than 500 meters away from a station. 

Once you have your station locations, it’s quite common to then draw a radius around each stop to simulate the catchment area. In other words: How much of the city can I service with this station and how far will people be willing to walk in order to get there? However, this distance, which is the radius of the circle, usually depends on the type of transit. Oftentimes people are willing to walk further in order to get to faster transit service.

But what’s most interesting about this radius of demand is that it’s entirely dependent on the fabric of the city. Take for example, the following two maps from Seattle, which I have taken from Walker’s blog. On the left is a suburban setting and on the right is a downtown setting. In both cases, the red circle represents a 1 km radius.

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Now, if humans could fly over barriers, such as highways, and every Seattle resident was willing to fly exactly 1 km to a transit station, these two radiuses of demand would be perfectly accurate. But since that’s not the case, we instead need to look at what actually represents a 1 km walk – those are the blue lines in each image.

Because once you do that, you realize that the cul-de-sacs and highways on the left make it impossible for most of that radius of demand to actually walk to the station in under 1 km. So the catchment area actually becomes much smaller. On the other hand, if you look at the image on the right, you’ll see that the tried and true city grid is actually remarkably efficient for walking. Almost all of the circle is serviced.

So as the Eglinton Crosstown LRT makes its way through the center of Toronto, I think it’s important to keep in mind that it’ll be cutting through quite a few different kinds of street grids. Some of them will be highly conducive to transit usage and others not as much. And in many ways, this is one of the greatest challenges of transit investment. The track itself is only one part of the puzzle.

That’s why the City of Toronto is also undertaking a planning exercise called Eglinton Connects. Its intent is to leverage the opportunities, as well as address the challenges, that will result from Metrolinx’s Crosstown LRT. If you’re interested in the future of Eglinton Avenue, you should consider getting involved. Oftentimes it’s only the critics that speak up. But that’s not the best way to build anything.

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