by Clay Martin – Research Analyst at D3
Light rail in Detroit faces an uncertain future. After years of planning and almost $100 million in dedicated funding from the Kresge Foundation, its M1 Rail partners, and the federal government, Mayor Dave Bing and Governor Rick Snyder announced in December that the M1 Rail project was canceled. In its place they proposed a bus rapid transit (BRT) system for southeast Michigan. In early January, they changed their position and stated that light rail was still possible in Detroit, although with a significantly shorter route. (A few days later, M1 Rail executive Matt Cullen indicated that the “light rail” would actually be a streetcar.) The shorter Woodward light rail/streetcar line will operate in conjunction with the new BRT system, though more changes to the transit plan may occur.
While the notion of rapid bus service may be unfamiliar to our region, it is worthwhile to consider the feasibility and desirability of a regional BRT system under the management of a dedicated regional transit authority (RTA). After all, legislation was recently introduced in Lansing to create an RTA and BRT does have certain advantages over its rail-bound counterpart. It is less expensive, with light rail costs per-mile between 150% and 5,000% greater than BRT, depending on the extent to which BRT elements such as grade-separated lanes are implemented . And, if done right, it can be a genuinely rapid form of transit. One comparison of BRT and light rail systems found that five out of six BRT systems had higher average operating speeds than light rail. 
Despite this, transit advocates in southeast Michigan have every reason to be skeptical. After all, the Suburban Mobility Authority for Regional Transportation (SMART) bus system cut nearly a quarter of its service in December in the face of reduced revenue from property taxes and its inability to renegotiate union contracts. Even before the cuts, fully 41 percent of suburban Detroit communities voted to opt-out of SMART, preferring to forgo bus service rather than pay a .59 millage. 
Many will read in these numbers a story familiar to southeast Michigan, a persistent inability to cooperate as a region in order to achieve planning goals, whether they are related to land-use, water and the environment, or transportation issues. Is there any reason to believe that a new RTA would be able to garner any more “buy-in” across southeast Michigan than SMART? At this point, any answer to this question would be purely speculative. So here’s another question: would a new RTA need to garner more regional support than SMART already does? Do the Detroit suburbs that currently opt-in to SMART form a geographically coherent and financially sustainable service area for a regional transit authority on their own? In other words, if we limit our attention to those communities that currently support a regional public transit system, do we still have the makings of a viable BRT service area for southeast Michigan?
Back to Basics – Do we have a coherent transit service area in our region?
To begin, we need to decide what “coherent” means when applied to a regional transit service area. To do so, flash back to high school geometry, where we learned that areas can be classified as “convex” or “non-convex.” In a convex area, you can draw a straight line between any two points within the area without leaving the area. Convex shapes don’t have kinks along their edges, and they don’t have holes. American cheese is convex; swiss cheese is not. See Figure 1.
Let’s call a transit service area coherent to the extent that it is convex. American cheese is coherent, Swiss cheese less so, and Swiss cheese with a bite out of it is least coherent of all. Now consider Map 1, which shows the communities in southeast Michigan that currently opt-in to SMART bus service, as well as Detroit, which opts-out but still receives service. We will restrict our attention to these communities, and consider their potential to support regional transit service. These communities do form a fairly coherent transit service area. With the exceptions of Bloomfield Hills, Lathrup Village, and Orchard Lake Village, there are few holes in the area. And with the exception of Walled Lake to the west, all communities are connected to all other communities in the area. That is, you don’t have to leave the service area to get from one community to another. While it would be nice if the other 41% of suburban communities opted-in to the system, at least they are largely located on the fringe of the tri-county region. A pattern in which many inner-ring suburbs opted-out and many outer-ring suburbs opted-in would be much less coherent.
Unfortunately, geographic coherence is not enough to ensure a viable transit system. (Your high school geometry teacher might call it necessary but not sufficient.) In addition to coherence, the communities that make up a service area must also be relatively dense (geographically speaking) and fiscally sound. Table 1 lists the minimum housing and employment densities required to sustain light rail, bus rapid transit, and conventional, less frequent bus service.  The theory behind Table 1 is fairly straightforward. More expensive systems, such as light rail and BRT, require more customers, and hence higher population densities, to be viable.
To understand what Table 1 means, let’s use it to estimate the commuters per stop needed to support conventional buses and BRT in Detroit. For this purpose, I’ll define a regular commuter as someone who has worked fifteen or more hours per week for forty or more weeks in the previous year. There are 196,301 such commuters in Detroit, or 0.53 per household.  If we define a bus stop’s market as households within a half mile of the stop, then we would conclude from Table 1 that 800 regular commuters per stop would support conventional bus service, while 1,600 per stop would be required to support BRT. While this back-of-the-envelope calculation may help us visualize the densities involved, we point out below that density requirements apply to the entire corridor, not to individual stops.
At the time of this writing, we did not have employment numbers for the Detroit region, but in Map 2 we have classified areas according to which mode of transit their population densities would support.
Before we look at this map in detail, a trio of caveats is in order. First, density requirements apply to transit corridors as a whole, not to the block group level, which we have mapped here. As a result, we cannot conclude from this map that an entire corridor is unsuitable for a certain transit mode simply because it contains block groups with unsuitable densities. For example, the Woodward Corridor may very well be suitable for bus rapid transit, and even light rail, despite the fact that some areas along the corridor lack the density to support these modes. Second, certain areas which are primarily industrial or commercial, such as stretches of Gratiot Avenue in Detroit, will appear to not be viable transit corridors when considered only from the perspective of population density. This is not necessarily the case. Minimum densities apply to the entire transit corridor, and they include employment as well as population densities. Areas that appear to be sparsely populated may very well contribute to the viability of a transit corridor by serving as places of employment. Finally, the following maps only provide a static portrait of the region; they do not reflect the potential for BRT to catalyze growth and encourage higher density along corridors in the future.
With these caveats in mind, we can see from Map 2 that the proposed BRT lines follow some of the most viable corridors in the Detroit region. While densities that support light rail, and even BRT, are currently limited to central Detroit, Hamtramck, the Woodward corridor, and a few scattered areas north of Eight Mile, there are many areas on the cusp of being viable BRT service areas. Only one or two extra housing units per acre would provide the density these areas need to support BRT.
Unfortunately, most growth is currently occurring on the fringe of the tri-county region. From Map 3, we see that “Opt-Out” areas and areas in the far northeastern reaches of the SMART service area have experienced the most growth over the last decade. The majority of areas in Detroit and its inner ring suburbs have actually lost population over the same period. Opponents of regional public transit will point to this as evidence that public transit, whether BRT or light rail, is destined to be under-utilized and unsustainable. Proponents will point out that the Detroit region is at a critical inflection point. It can either continue to grow outwards, away from the city and into an auto-centric oblivion, or it can take this opportunity to invest in a system that will lure residents back to Detroit and its inner-ring suburbs.
So far, we have only looked at whether or not the Detroit region can support a BRT system. From another perspective, we can ask how best a public transit system, BRT or otherwise, can support the Detroit region. In particular, we can ask how a system can connect the least mobile residents of southeast Michigan to jobs throughout the region. Map 4 shows the distribution of households that could benefit most from a viable transit system, those households that do not have access to an automobile. We can see that while auto-mobility is enjoyed by the vast majority of suburban Detroit households, there is a concentration of households in Detroit that do not have access to private transportation. The proposed BRT system could connect these areas to jobs.
Let’s Get Moving
It is not our intention in this article to takes sides in the light rail versus BRT debate. But Map 4 does remind us that for many residents of southeast Michigan, a viable transit system is crucial to access jobs, healthcare, and other essential services. No matter what form the region’s future transit system takes, we need to get moving.
 Levinson, H., Zimmerman, S., et al. “Bus Rapid Transit: An Overview” Journal of Public Transportation. 5 (2) 2002
 U.S. General Accounting Office. “Bus Transit: Bus Rapid Transit show promise” 2001
 Accessed online at http://www.smartbus.org/riderguide/smartservices/communitytransit.
 Lee County Bus Rapid Transit Feasibility Study: Final Report. Accessed online at http://www.rideleetran.com/pdfs/Lee%20BRT%20Final%20Report_042808.pdf
 American Community Survey, 2006-2010.
This article has been revised to reflect the following correction:
The article misstated the city of Detroit’s status in the SMART service area. It stated that Detroit was an opt-in community in the SMART system; Detroit is actually an opt-out community that receives service. D3 regrets the error.