Jul 5, 2009

Rectilinear (grid) vs Cul-de-sac street layout

One theory of urban planning is that non-grid-like streets help to break-up the flow of traffic from the business downtown rectilinear block, into a softer residential flow. Traffic would flow from the small cul-de-sac and collect onto wider collector streets. (The satellite image shows Meheula Parkway -- in yellow -- as the larger collector road. Note that Meheula Pkwy then shunts traffic onto the H-2 interstate freeway)

The pic ABOVE, ranks streets in order of size/carrying capacity: Alley, Access, Sub-Collector, Collector and Arterial -- an excerpt from the City & County of Honolulu, Department of Planning & Permitting, Subdivision Street Standards.

Similar to the arterial system of the human body, where the peripheral and minute blood vessels in our fingertips are adequate to provide circulation at the extremeties, vs the larger blood vessels closer to the heart. In theory,
traffic would merge together collecting more and more cars from the suburbs, gathering them up onto wider and wider vehicular veins, transporting commuters to the heart of Honolulu. Sounds poetic, but in practice, one accident during rush hour, and everyone's screwed: One way in; one way out. People who live in Ewa and Waianae can attest to the frustration (and some argue, lower property values) this causes.

Another theory of urban planning (more common in the older neighborhoods of Oahu and downtown) is the rectilinear block layout, offering multiple paths to get to the same destination. If one lane shuts down, drivers can bypass the area. Traffic can flow (and backtrack) around the grid, circumnavigating the blockage. This layout is more typically found in older neighborhoods.

A criticism of the rectilinear block plan is that it promotes speeding. If drivers can see an unobstructed straight path, they tend to accelerate.


Cul-de-sac streets provide a meandering organic flow that softens the flow of residential traffic. Also, a cul-de-sac provides greater opportunities for children to play. There's less through-traffic and therefore less overall traffic. Unless they're lost, most cars are your neighbors'. Also, the circular orientation encourages interaction. When the handful of (sometimes shared) driveways in the cul-de-sac face toward the center and each other, it's a bit harder to ignore each other. There can be a greater warmth and familiarity that is sometimes lost in modern communities.

RECTILINEAR is still better:

Speaking as a person who has gotten lost in the maze of new suburbs that included numerous dead-ends, I emphatically prefer grids. To me, the argument about speeding thru perpendicualr grid streets can be assuaged with stop signs and traffic lights. At least in the movies, kids seem to play in the streets all the time without getting hurt. And in terms of fire safety, multiple means of access to a site are preferred.

The next time you walk through and neighborhood to visit friends, think about the street layout. How does it make you feel. Do you feel trapped, confused? Do you feel safe? Are there useable sidewalks to walk dogs or for jogging? Is there on-street parking for guests? How do you think the neighborhood planning affects property value?