I Can See for Miles and Miles: What's the System Used for Gauging Distances on Highway Signs? There Isn't One!
It turns out the Department of Transportation has its own ideas of what constitutes "city limits." Yet this system strongly relies upon its deployment in " a case-by-case basis" -- meaning, in reality, there is no system.
This, it would seem, is what we get for living in a haphazard collection of 50 states and 3,141 counties.Traditionally in France, for example, the distance between cities is uniformly measured from city hall to city hall (with the exception of Paris, which uses Notre Dame as a central point).
That's not how we do it here. According to the Manual on Uniform Traffic Control Devices (section 2D.36):
The distance shown should be selected on a case-by-case basis ... A well-defined central area or central business district should be used where one exists. In other cases, the layout of the community should be considered in relation to the highway being signed and the decision based on where it appears that most drivers would feel that they are in the center of the community in question.
But wait -- they're not finished:
The top name on the Distance sign should be that of the next place on the route having a post office or a railroad station, a route number or name of an intersected highway, or any other significant geographical identity. The bottom name on the sign should be that of the next major destination or control city. If three destinations are shown, the middle line should be used to indicate communities of general interest along the route or important route junctions.
But wait -- I asked Nancy Singer at the Department of Transportation to clarify ... and she did:
The distance would likely not be exactly to the "dot on the map," but would be measured to the theoretical boundary or limit of the central business district or center of the community. This theoretical boundary might or might not coincide with the legal corporate boundary of the municipality. The distances will rely somewhat on the development pattern of the community.Well, there you go. So that, ladies and gentlemen, is why the DOT thinks that Daly City is 10 miles wide.