Advisory Cornering Speeds Aren’t Made-Up Numbers (Except When They Are)
From the April 2016 issue
Pop quiz: The yellow diamond-shaped sign on the side of the road says you should take the upcoming curve at 35 mph. At what speed can you actually travel through the bend" 45 mph" 55" Can you double it"
Depends on the car, right" It?s no surprise that the suggested speeds through curves fall well below what the average BMW can manage. Traffic engineers design for trucks, inclement road conditions, inept drivers, and ambulance-chasing lawyers, not P Zero?shod sports coupes. But it also depends on the curve, and how reasonable that suggested speed actually is. We looked into how recommended cornering speeds are set, and we found a mishmash of malleable procedures that are inconsistently applied. That?s why a 45-mph curve in Happyland, Oklahoma, often looks nothing like a 45-mph bend on SoCal?s Angeles Crest Highway. To no one?s surprise, research indicates that these curve advisory speeds are among the most disregarded signs on the road. Even as the Federal Highway Administration (FHWA) has formalized its procedures in recent years, there?s still wide Âlatitude for how state, county, and municipal agencies determine the curve advisory speeds on the roads they manage. The FHWA?s 35-page guidance document, published in 2011, offers sanctioned methods that fall into the three following fundamental categories, but engineers aren?t obligated to abide by them.
ROADWORK AHEAD
Finally, Congress Gets Something Right. (Sort Of.)
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