Sunday, June 22, 2008

Courant Op-Ed: Engineering policy and street dangers

Great op-ed in today's Hartford Courant, by Downtown New Haven architect and planner Robert Orr:


Engineering policy over the past 50 years has nudged streets toward increasing mobility. Mobility is the term used by engineers to describe measures to make drivers feel safe at higher speeds, called design speed. The tools for increased design speed are wide and multiple driving lanes; one-way streets; absence of parking and visual obstructions, especially near intersections; streamlined corners with large radii; and highly legible signage. All these measures make drivers feel safer at higher speeds.

Automobile design too contributes to mobility. The average family car today can run circles around the meanest muscle car of the 1950s. The combined mobility of streets and cars make ordinary drivers feel safe at roaring speeds, frequently exceeding 50 and even 60 mph on city streets.

Some would argue that speeding is a problem of enforcement, as posted speeds are being violated. However, when posted speeds are significantly lower than design speeds, law enforcement takes on the bait-and-switch air of entrapment.

All these automotive assets spell liabilities for pedestrians, especially now that studies demonstrate 37 mph to be the threshold for guaranteed pedestrian fatality. By contrast, speeds below 20 mph rarely result in serious injury. Other studies now link accidents directly to street width; as streets widen, fatalities increase exponentially.

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