The entire field of traffic engineering abounds in counter-intuitive findings. A study in Finland showed that adding reflector posts to a curved highway actually increased accidents. It turns out that a curve marked with reflectors and advisory speed signs can lead motorists to go faster around the curve than they ordinarily would. Similarly, “Children at Play” signs do not slow drivers down, or reduce accidents, and some transportation departments have stopped posting school zones for this reason.
As Vanderbilt accesses the matter, “There is a simple mantra you can carry about with you in traffic: When a situation feels dangerous to you, it’s probably more safe than you know; when a situation feels safe, that is precisely when you should feel on guard.”
--Patrick T. McCoy, Geza Pesti, et. al. "Dynamic Late Merge-Control Concept for Work Zones on Rural Interstate Highways." Journal of the Transportation Research Board. 2001 1745 20-6. DOI 10.3141/1745-03
--Vanderbilt, Tom. Traffic: Why We Drive the Way We Do (and What It Says About Us). New York, Toronto: Alfred A. Knopf, 2008.