Market St, Octavia Blvd, and Hwy 101 in San Fransisco
We all understand that intersections are dangerous areas within transportation systems. Intersections are where high numbers and varying types of users converge in a small area riddled with points of potential conflict. We read a chapter earlier this semester in class addressing the ways in which "more dangerous streets are safer" because they force the driver to remain engaged in their driving and likely facilitate slower operating speeds. While the author made several compelling points it's difficult to believe more complex transportation networks actually reduce fatal crashes, particularly on busy arterials, primarily because drivers are resistant to changing their driving patterns, regardless of road design. User behavior is also unfortunately one of the most challenging variables to influence for us as planners and engineers.
A recent study conducted by the navigation company Waze identified the most dangerous intersections for pedestrians and cyclists in three American cities- San Francisco, Los Angeles and Boston. Each city created it's own metric to measure danger and they were not measured against each other metrics. The results are startling, as are the designs of some of the intersections, such as the one above found in San Francisco.
I felt this study could have been more comprehensive- it was more a sample than a study- but it was interesting to see how each city measured danger in different ways.
San Francisco focused on intersections within a previously designated 'high injury network' where the majority of traffic related injuries occur. SF use data from 2008-2012 and weighted severe and fatal injuries more heavily. Los Angeles used crash 2009-2012 data from LADOT and weighted pedestrian and bicyclist injury more heavily to determine intersection danger. Boston use police and ambulance data from 2012-2014 to determine relative danger.
None of these methods are perfect, for example, by only monitoring police and ambulance data, Boston is missing traffic incidences that go unreported. Bicycle traffic incidents often are not reported, particularly if there is minimal bodily injury.
What do you think of this study? Did your group use any of these metrics in determining speed limits for your projects? Now that you've seen this, would you consider adding any of these metrics to be useful? Do you think road design really has the power to influence user habits?
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