This interesting speed limit notification is displayed at the entrance and exit to Sunflower RV Resort in Surprise, Arizona.
It’s effective because it got my attention, and I suspect anyone who sees it. Such a specific speed limit needs an explanation. Here’s mine.
One reason is the odd number easily attracts attention. Another reason is it makes sense.
The time-honored very low 10 miles per hour speed limit can’t be maintained.
Today, most automatic transmission idles at more than 10 miles per hour. Thus, everyone was already speeding, so why bother trying to obey the sign?
By increasing the speed limit, at least no one will be speeding, and it remains within a reasonable speed in a neighborhood.
Give or take, other low-speed signs are 15 and 25 in school and hospital zones.
I still enjoy the veiled threat sign posted on a military base. “We are eagerly seeking volunteers to test our radar guns.”