Discussion

The Arroyo Seco Parkway illustrates the challenge presented by older highways that were constructed at a time when less was known about design criteria and its relationship to highway safety and operations.  In this case, the highway also has a historic context as well as a river and development near the highway right-of-way.  The impacts associated with reconstructing this type of highway to meet current criteria are often unacceptable.

The choice of median barrier illustrates the tradeoffs associated with mitigation measures themselves.  The height and type of barrier affects horizontal stopping sight distance, the ability to contain and redirect large vehicles, headlight glare, aesthetic considerations, and constructability.  Looking at the characteristics of each specific site is important for the careful weighing of these tradeoffs.  For the Arroyo Seco Parkway, its crash history, traffic volume and composition (large trucks are currently prohibited), horizontal alignment, future maintenance requirements, and context are all important variables.

This case study also illustrates that mitigation measures can be implemented on projects with a smaller scope—3R projects or safety–improvement projects.  Lower-cost, lower-impact measures such as improved delineation, pull-off areas, or the addition of an auxiliary lane for deceleration can have a significant safety impact at some locations.  

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