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Six Tips for Better Stop Signs
2. Comply with MUTCD.
What is the Right Size?
Bigger is better. Although the most popular size for a stop sign is the 24” octagon, the MUTCD regulations note that 36” tall stop signs should be used expressways, 30” stop signs should be used on conventional roads and 24” stop signs is the minimum dimension. 18” stop signs, while popular for factories and non-public roads, are not MUTCD compliant.

The chart above shows a typical installation. The distance from the bottom edge of the sign to the level of the edge of the pavement is shown as a dimension not less than 5 feet. Yet, Where parking or pedestrian movements occur, the clearance to the bottom of the sign shall be at least 7 feet. The distance between the edge of the pavement and the near edge of the sign should be not less than 6 feet.
Signs Need to be Reflective
According to a portion of the MUTCD that has remained, essentially, unchanged since the 1960's, "Regulatory, warning, and guide signs shall be retroreflective or illuminated to show the same shape and similar color by both day and night." In particular, stop signs need to be, at least, ASTM Type I reflective (Engineer Grade). Yet, the trend is that brighter sign materials (high intensity and diamond grade signs) are increasingly favored
It is also important to understand how the two terms, "Reflectivity" and "Retroreflectivity" differ. Although reflectivity is often used loosely to mean, in fact, retroreflectivity, the latter term has a more precise, scientific meaning. In particular, Retroreflectivity is defined as the ability of a sign (for example) to redirect light back to its source (a car with headlights).
Compare this with the notion of "Diffuse Reflection" or "Reflection". In this case, the light that shines on an object is reflected diffusely in many directions. An ordinary metal sign is diffusely reflective (e.g. it is visible to us). A "Retroreflective" sign, in contrast, focuses or redirects a majority of the light energy directly back to the light's source. This is what makes a high intensity sign, for example, appear so bright at night.
Not Just Public Roads
The scope of the MUTCD standards has been expanded. It no longer just covers public roads. As long as your facility, parking lot, roads, etc. are "open to public travel", the signs that you use must comply with MUTCD standards. For example, these signs must meet the same level of retroreflectivity that are required for traffic signs on public highways and roads.