Memo: Sustainable Transportation 5

Part of a series of “reading memos” that offer a brief summary of interesting academic content along with my personal reflections. This one covers Chapter 5 and 10 (streets and parking) from Jeffrey Tumlin’s Sustainable Transportation Planning.


Streets need to accommodate a wide variety of uses (e.g., autos, pedestrians, bicyclists, transit, and goods delivery), and holistic street design requires considering factors such as priority of travel modes, land-use context, relationship to other streets, and available right-of-way. “Complete Streets” (i.e., not solely auto-centric) are those designed for all modes and people of all ages & abilities – these have health, safety, mobility (network capacity), and environmental (reduced carbon emissions) benefits.

Principles for street design include reflecting the landscape (considering sensitive areas, topography, views, wind/sun patterns, etc.) and integrating transportation with land-use planning (e.g., encouraging walking for most trips in mixed-use neighborhoods, prioritizing frequent transit near dense land uses, and spacing retail along a street corridor that’s not too wide). While conventional approaches (i.e., functional classification) define streets based on their ratio of mobility (capacity) and access, a more modern approach categorizes streets by their land-use context (e.g., downtown, neighborhood, commercial, residential, or industrial) and prioritized mode (e.g., “transit boulevard”).

Parking spaces consume land (~330 sq. ft. each), cost money (~$40K-60K each), reduce housing affordability, worsen traffic congestion, generate GHG emissions (via increased VMT), pollute water (via runoff from lots), and destroy the walkability of neighborhoods. Existing tools for estimating parking needs such as the ITE Parking Generation manual and the ULI Shared Parking Model have led to inflated parking requirements as they tend to be based on peak demand estimates with no availability of alternative transportation services.

Principles for parking management include pricing/limiting to achieve 85-90% occupancy, ensuring the public perceives that parking is always available, sharing facilities to maximize efficiency/usage (between land uses with different times of peak demand), limiting curb cuts on main (transit-priority) streets, using parking as the (most effective) lever to manage roadway congestion, and involving the business community when designing policy. Some strategies for parking management include “Park Once” (including as many spaces as possible in a common pool of shared parking walkable to many destinations), creating Commercial/Residential Parking Benefit Areas (where parking revenues directly benefit the areas where they are collected), investing revenues in Transportation Demand Management (TDM) programs like universal transit passes, unbundling parking costs from new development, requiring spaces for carsharing services, mandating parking cash-out programs for employers, removing minimum parking requirements, and funding parking facilities with user fees.


It’s interesting how the old standards for street and parking management from ITE/ULI/etc. likely had good intentions yet have led to so many unintended negative consequences (i.e., extreme auto-centricity and excessive/expensive parking requirements). In retrospect, the users of these guides could have realized their limitations (not considering pedestrian access or availability of public transit, only considering peak usage, etc.) and adjusted their planning accordingly, but simply following the guides blindly was likely the path of least resistance.

Correcting these past mistakes seems like it will require tactics that are as much about psychology as engineering. Making people feel that there’s “enough” parking available at all times and alleviating fears about overcrowded parking with new development are frustratingly necessary now, given how entrenched the idea of unlimited free parking has become in our society. Originally, I believed it would be easiest if we just eliminated nearly all parking to force mode switches, but I see how that’s not at all politically feasible in most environments.

I also now realize that the importance of local context cannot be overstated – there will always be places that need wider/narrower streets or more/less parking, depending on the land uses that exist around them. It’s not possible to take a perfect “complete street” and expect it to work everywhere, but at least the set of design patterns presented here can be mixed and matched as appropriate. The interconnectedness of transportation planning and land use planning means that sometimes making desired changes will be more difficult, as it’s relatively easier to modify a street layout than to change the entire context of buildings and land uses in a given area.

More relevant content about parking:

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