October 7


City of Chanhassen (Minnesota) staff emailed me wondering if I had an opinion on dynamic message signs.  These signs are usually built with LED lights and the information on them can change every few seconds.  Chanhassen's ordinance bans these types of signs, but they are dealing with a variance request and are trying to decide if they should deal with the variance request or change the sign ordinance.  The easiest way to deal with the signs is either totally allow them or totally ban them.  As a traffic engineer on my high horse, these signs are a terrible idea.  They are purposely designed so the motorist will read the sign instead of paying attention to their driving.  Falling off of my high horse – our society has decided to allow some distraction (proof = billboards). 

I did some googling and I also queuried my fellow traffic engineers on a bulletin board through my professoinal society.  It turns out a lot of the relevant research out there is from my backyard.  The League of Minnesota Cities has a brief primer on the topic that helps frame the debate.  The City of Minnetonka commissioned a study that looks at the issue in depth. 

After reading through a lot of the research, I have come to a middle of the road conclusion.  We should allow these electronic, changable signs as a property rights decision (my personal view, I am not a lawyer).  On the flip side they need to be regulated by local governments for public safety reasons (they also need to be regulated for their impact on adjacent properties – but that is an aesthetic issue not a safety issue).  To manage the distraction (and degradation of motorist safety) the signs shouldn't be allowed to change more than every eight seconds (plus or minus depending on roadway speed) so a single motorist only sees one message.  This minimizes the distraction caused by these signs while protecting property rights.

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Mike Spack

My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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