How are distances listed on freeway signs between cities determined?
Do you ever wonder how the miles between cities are calculated for freeway signs? There are a lot of questions that go along with this idea, like what do the distances measure? When a sign says, for instance, that you have 10 miles to drive until you reach St. Louis, does that mean to the center of the city, or to the first exit, or to the city limits?
In an interview with a CalTrans employee (CalTrans is the state agency that builds and maintains California roads and so on), he said that the company measures the distances by driving and recording the miles on the odometer. There are also markers every mile along some freeways and highways.
As far as what the numbers represent on those signs you see, CalTrans said that they consider what part of the city travelers would be most interested in getting to, which is usually the center of the city. The first exit into the city is the alternative destination a freeway sign will prep a driver for.
So as you can see, it's actually pretty arbitrary. I always thought the distances meant from one city limit to another, but then once I started driving, I realized this was unlikely, as I drove between cities and figured I had driven fewer miles than was indicated on the signs.
I hope this was helpful... a little bit of trivia! This question isn't as relevant for the signs that show how much longer until you reach an exit or junction or so on... those need to be more accurate!
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