Urban planning community | #theplannerlife

# Thread: Legibility of signs based on speed

1. ## Legibility of signs based on speed

Here's the question for the throbbing brain:

I am looking for information (charts/graphics) on the readability/legibility of signs based on speed of traffic. It would also have information as to size of lettering, etc. I found a bit of info on the US DOT website, but not exactly what I'm looking for. Pointing me in the right direction would be extremely helpful! Thanks.

2. Originally posted by RandomPlanner...
Here's the question for the throbbing brain:

I am looking for information (charts/graphics) on the readability/legibility of signs based on speed of traffic. It would also have information as to size of lettering, etc. I found a bit of info on the US DOT website, but not exactly what I'm looking for. Pointing me in the right direction would be extremely helpful! Thanks.

3. MUTCD suggests 40 feet of legibility distance for each inch of letter height. There's also the Standard Highway Signs manual. No table for speed or average time to read message. You could assume a time to read the message (based on number of bits of information), then with the road speed figure out how big the letters need to be to have them legible for the needed time. There's been alot of research lately with the Clearview font development, so the info is probably out there. http://www.clearviewhwy.com/ has some links to research.

P.S. Random Planner, sorry for stealing part of your name, brought this from another board and didn't check here first.

Ran into a formula used by some of my company's offices. I have no idea where it came from or on what research it is based. YMMV.

Dependent on:
A - # of statements or lines of text
B - Speed limit of road (MPH assumed)
C - Lateral distance from furthest travelling lane (feet assumed)

Code:
`( ( ( A + 6 ) * B ) / 100 ) + ( C / 10 )`

4. ## Wow!

Originally posted by Random Traffic Guy
Ran into a formula used by some of my company's offices. I have no idea where it came from or on what research it is based. YMMV.

Dependent on:
A - # of statements or lines of text
B - Speed limit of road (MPH assumed)
C - Lateral distance from furthest travelling lane (feet assumed)

Code:
`( ( ( A + 6 ) * B ) / 100 ) + ( C / 10 )`
I stared at this formula for a good 2 minutes before I even thought to hit the reply button! I am interested to plug in some numbers and see what comes of it...and in awe that such a formula exists.
Questions: 1) what does YMMV stand for?; 2) am I to assume that the outcome (x) is the size in inches of the lettering??
(Does is prove that I went into planning to avoid math problems??)

Off-topic: And in gratitude for the formula, I am willing to let it slide that you stole part of my name, Random TG!

5. Yes, outcome is size in inches. No awe required, probably ripped from some research paper. I'm trying to find out the source.

YMMV = your mileage may vary

EDIT:
Found it. Architectural Signing and Graphics by Follis and Hammer. (1979)
So I would not call it current or for use on roads, but good enough for development "coming soon" signs, site name signs and the like.