Alleys! They’re in the news! To be honest, they’re generally pretty boring places, perhaps undeserving of a love letter. Most people might even dislike them, even avoid them at all costs. As with most small, mundane details of the built environment, I think we sometimes take alleys for granted in Minneapolis and St. Paul, and it’s worth discussing their virtues. Especially since nearly all development in the Twin Cities since the mid-1950s has been alleyless.

Benefits to the Public

When we evaluate any individual urban design element (such as front steps or doors or window placement), benefits tend to look pretty small. A great, safe street or place typically comes about when the sum of each of these parts is added up. And we urbanists need to admit that not societal every problem can be solved by land use or transportation. With that said, I believe alleys contribute positively to the public (not just private owners) owing to their design. A few examples (in no particular order):

• Hiding things from the primary pedestrian realm: Alleys are a great place to tuck things that detract from a pleasant walking experience like garbage cans, dumpsters, utility poles and lines, and bland garage faces, which would otherwise be the primary face fronting the street (more on that later). These may not be too terrible on a low-density single family detached residential street owing to the relative lack of garbage and low frequency of pickup. If you’re a fan of intensification over time (including slowly adding neighborhood commercial uses and denser multi-family buildings), this is important.
• Reduce total curb cuts on a given block: A residential street without an alley will likely have a curb cut for every parcel. This is true even for denser buildings like townhomes or apartments. Some amount of parking will either be required or provided, and access will come from the street without an alley present. While most Minneapolis and St. Paul driveway curb cuts come up to sidewalk level and have slow-moving cars, this is still a safety issue for pedestrians; about 500 people a year are killed (and over 100,000 injured) in driveways in our country. A block with 30 houses and two curb cuts for alleys (with slow moving cars as well owing to the design) is better than a curb cut for every house.
• Increase street tree coverage: Every curb cut and apron is roughly ten feet of boulevard space paved over in lieu of space for a tree or other plantings. These serve measurable benefits to society. While a narrow eight to ten foot driveway offset by 30 feet of trees and boulevard in a single family detached neighborhood may not be a huge deal, start densifying and your results may vary. For single family home teardowns on lots without alleys, a double garage and driveway will be worse than what it replaced.
  

  Front-facing double garages are the likely outcome without alleys for teardown situations.

• Narrowed streets or re-purposed right of way: Related to the bullet above, every curb cut demands pavement to get cars in and out of a driveway, pavement that could be used for something else. The easiest option is more on-street parking, but it’s not hard to imagine the space being used for other things like stormwater retention bulbs. The same number of on-street parking spaces on a street with frequent curb cuts could be provided with a narrower street width with chicanes if an alley is present, or simply less total public infrastructure with only one-side parking (in practice, the city would turn land back to owners on each side at the next street reconstruction).
• Garbage collection costs: This one may be a stretch. I have no data, but I have to believe running a truck down a 12′ wide alley can collect garbage from both sides quicker, and therefore at less expense, than running down a 40′ wide street with the same number of homes.
• Limiting stormwater runoff: I discussed street space elements that can mitigate runoff without curb cuts, but a shared 12′ wide alley for an entire block, even for single family homes, presents an opportunity to maximize total permeable surface area given similar home and garage sizes:
  I compared a 30’x30′ house footprint with a 15′ required setback on the front yard in various layouts on a standard Minneapolis lot (40’x125′ plus half the width of a 12′ wide alley). I was surprised to see the best case for limiting impermeable surface coverage from driveways is the front-facing garage “snout house,” with the attendant public realm issues discussed earlier. However, lots with alley-facing or -abutting garages made up the next four best results, keeping paved surface to under 10% of the lot. Side driveways fared much worse. And, contrary to (what I believe to be) widespread public opinion, backyard space isn’t really sacrificed, though this is more of a private benefit anyway, and would be weighed against the benefit of having your garage attached to the home’s living space.

Redevelopment is the Key

To me, the biggest benefit of alleys is the ability to support infill and redevelopment, which has overall positive benefits to neighbors (via supporting more shopping, better transit, etc) and the city’s tax base. The natural path to adding density along alleys are Accessory Dwelling Units. I’ve talked about them before, and Minneapolis legalized them last year, so it’s not worth saying much.

Yes, an ADU could be tucked at the back of the lot with a side-driveway lot configuration (above). I suspect homeowners are less likely to build one in this situation; sharing the driveway with the tenant and likely having the unit’s windows face their yard is less desirable than an ADU that mostly faces the rear. Alley-fronting residential also upends the benefits of tucking away the nasty parts of urban life from pedestrians, turning them into a public space resembling many Japanese streets (which is still probably okay). It also raises questions on accessibility given the state of alley surfaces (again, we’ll discuss this later).

Beyond ADUs, if we want to encourage small-scale infill, alleys play a major part in making them both pencil out as well as mitigate the issues discussed earlier in the post. For example, a single-lot project is going to be difficult to squeeze a building, side setback, and driveway onto a 40′ wide lot and still fit the units required to maintain profitability (to say nothing of ADA compliance, etc). Without an alley, a developer might choose to build something like this (if it’s even allowed by zoning code):

Even this could only be done with the parking minimum reduction passed earlier this year in Minneapolis. If an alley were present, we could instead get something more like this:

If a developer wants to piece together just a few lots for a courtyard-style building, an alley once again greatly improves the frontage:

I suspect that not building alleys in many suburbs, even ones that retained a rigid street grid, was at least in part an intentional move to keep redevelopment out.

Drawbacks, Room for Improvement

The major drawback of alleys is the cost. They don’t pave, re-surface, or plow themselves, and a city would spend less each year without them. One could also make the case that they constitute a publicly-provided space primarily for private uses: parking cars or bikes, especially since alleys tend to not meet pedestrian accessibility requirements and have poor drainage owing to the lack of stormwater infrastructure.

I’m not sure on the latter points. Pro-urban people typically support filtered permeability or other measures to keep through-traffic (at least, motor vehicles) off residential streets. Walker Angell would call this a rat-run, and several Minneapolis neighborhoods (such as Lyndale) have implemented them. That vehicle traffic is almost entirely for private access doesn’t make the streets any less public. I’d also challenge the notion that most alleys are worse than many critical sidewalks in our cities from an accessibility viewpoint. This doesn’t excuse the current condition of our alleys or our sidewalks for pedestrians, only that the woeful condition isn’t specific to either. Further, while I’m not an expert on legal requirements for accessibility, many beautiful pedestrianized alleys seem to violate side slope, passable width, and surface requirements.

That said, alleys are narrow and therefore relatively cheap to resurface. We should do this more often in areas where they’re experiencing redevelopment or already have denser buildings with frequently-used back doors. It’s also not crazy to envision the city identifying places to increase the pedestrian network as redevelopment or infill occurs, focusing on using alleys as anchors (right).

Chicago has a great guide for greening alleys and implementing simple stormwater solutions for ones with poor drainage as well. And of course, even just a little bit of art goes a long way to making an otherwise bland stretch of garages into something interesting to walk by. Cities with alleys would also do well to update their lighting strategy to mitigate safety issues (or, perception of safety which is just as real). For those of you who made it this far and clearly care about cities, what do you think about alleys?