Sign Visibility Calculator

Min Letter Height applies the one-inch-per-30-feet rule, which is the accepted USSC minimum standard for basic legibility. Recommended Height uses a tighter one-inch-per-25-feet ratio, giving noticeably larger letters that leave margin for glare, weather, or a driver's divided attention — it's the number the calculator also uses to estimate sign width, since it's meant as the practical design target rather than the bare minimum.

Sign Width is derived from Recommended Height assuming a single line of about 10 characters at a letter-width-to-height ratio of 0.6 — a reasonable approximation for one short line of text. If your sign uses multiple lines, a longer message, or a wide logo alongside text, this estimate will undersize the actual sign needed, since it doesn't account for line count or message length beyond that fixed 10-character assumption.

Reaction Distance converts your vehicle speed to feet per second and multiplies by reaction time to show how far a vehicle travels while the driver reads, comprehends, and reacts to the sign. It's a placement sanity check — even a perfectly legible sign needs enough distance in front of a turn or exit for that reaction distance to fit, which is a separate concern from whether the letters themselves are large enough to read.

Three seconds is the standard traffic-engineering assumption for the combined time a driver needs to notice unfamiliar signage, read it, comprehend the message, and begin reacting — it's not just simple brake-reaction time, which is typically shorter. You can adjust this input if you're modeling a more complex or unusually cluttered sign environment that would need more processing time.