"AASHTO says what many experts avoid admitting: Speed reduces the visual field, restricts peripheral vision, and limits the time available for drivers to receive and process information. The faster you drive, the less you see. And when you finally do see someone headed into your path, it's too late to stop in time. The "go with the flow" justification for driving 40 mph around schools, homes, and storefronts causes preventable crashes, injuries, and fatalities."
"Engineers who read the Green Book will find this reminder about using judgment that goes beyond tables or graphs (emphasis mine): Design speed is a selected speed used to determine the various geometric design features of the roadway. The selected design speed should be a logical one with respect to the anticipated operating speed, topography, the adjacent land use, and the functional classification of the highway. In selection of design speed, every"
Most American cities have street networks engineered for comfortable but unsafe driving speeds. Many pre-automobile streets were modified to facilitate faster driving, creating hazardous conditions. Transportation professionals often default to long-established industry rules that favor vehicle speed and throughput, and state departments of transportation can reinforce those norms. Engineering guidance like the AASHTO Green Book is commonly used to justify designs that prioritize traffic flow over safety. Speed diminishes drivers' visual fields and reduces reaction time, increasing crashes, injuries, and fatalities. Engineers are not malicious; they follow standards and require reminders and applied judgment to design safer streets.
Read at Fast Company
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