October 13


Real World Sign Retroreflectivity Tests

By Mike Spack

October 13, 2011

Sign Inventory Sign Maintenance Retroreflectormeter

RrmeterThanks to federal regulation, all agencies need to keep an accurate sign inventory and ensure their signs meet certain retroreflectivity requirements (translation – know what signs you have and make sure the signs reflect enough light at night so motorists can see them). 

Robert Wunderlich (City of Garland Texas Senior Managing Director of Transportation/Engineering along with being ITE's International President) posted the following test results on ITE's Traffic Engineering Council bulletin board on the ITE Community page (if you're a member of ITE you really should get plugged into the ITE Community page – it's a great resource).  Thanks Robert for letting me share this!

Dear Colleagues:

Thanks to our friends at the City of Denton, Texas, we had the use of a retroreflectometer (RRmeter) for the past two weeks. 

We used it to see if we could use some leftover Engineer Grade (EG) materials to make comparison panels or calibration signs and I did a little nighttime measuring in my neighborhood.

New Engineer Grade Test Results



EG measurement


120, 50, 35











So, we have a lot of what we need already. Most of the paper exceeded these values.  We had to dig for some of this. We're looking for some older white signs that might be closer to the 50 and 35 values.  Most of the new EG white was around 100 cd/lx/m2.  It's hard to find new EG red lower than 17 or 18, but stopping's pretty important so setting a threshold around there is probably OK.  Most green is above 15 but we found a portion of a roll that measures 15. 

Rolls tend to vary considerably and it absolutely impossible to determine what the RR value will be just looking at it during the day.

Field Measurements

I highly recommend taking a RRmeter out during the night and checking signs.  It brings these values to reality and there's no substitute for going out and understanding what they mean.

Mr. Robert's Neighborhood (not in Garland, by the way)

I found New Hi-Intensity sheeting exceeds the minimums by an order of magnitude.  Signs really have to be quite bad to not meet the minimums, although the 3:1 white:red ratio gets some otherwise acceptable signs.  I will say that these signs do not reflect a bright, deep fire engine red (like a new Hi-Intensity one does) but it's not going to get confused with any other color either.

Quite frankly, I believe that any sign that doesn't meet these minimums would be judged unacceptable by any of us or our sign crews.  In fact, our crews probably would have much higher thresholds than the minimum.  Lot's of old EG signs still meet the minimum (even when they've been egged, and boy, there's a lot of that out there)  There's no way to tell what a sign will reflect at night by looking at it during the day.  Some signs that look pretty crappy in the day meet the RR mins.  Not saying that we should keep crappy looking signs up.  Also, I will say that even for the stop signs that didn't meet the minimums, it would be hard to say that you didn't know what you are supposed to do there (i.e., stop)  It's red, its octagonal, and it's not invisible (I mean really).

9-year old Hi Intensity Ground Mounted Street Name Signs (in Garland)

10 years ago, we started a comprehensive replacement of our really crappy (there's that technical term again) street name signs.  We finally got some funding when the Public Safety folks said they couldn't find the fires and the crooks cause they couldn't see the signs.  (See, we are part of Public Safety!)

Today, we checked a few of the signs in an area replaced in the second year.  These are hi-intensity beaded sheeting signs.  Our green RR values ranged from 43 to 47 (with no correlation to whether the sign was south-facing)  The ground-mounted green minimum is 15 and a 10 year-old sign made from the same material that has been up in our sign shop measured 66. 

The white values ranged between 210 and 236 (minimum 120).  The like-new sign in the shop measured 304.

So, we've had some deterioration but we're still well above the minimums.  The warranty is almost over and the signs will continue to function adequately.  The durability testing results I've seen indicate that the deterioration does steepen, but I'm betting we get 10 more years out of these signs.  We'll see (so to speak)

We did this project over about 5 years, and we plan to get more data to see what the deterioration has been.

Lite Research Summary (what I think I know now)

RRmeters are pretty cool.  Gotta get me one.

We are in pretty good shape with our street name signs.  Will they last till 2018?  I'm thinking they will, but eventually we will need to replace them, and we've got a ton of them.  Not an emergency.

Warranty does NOT equal sign life.

I'm not going to blanket replace.  I can't see replacing functioning signs.

If the white is good on a stop sign, it's pretty likely the red will be ok.

I'm concerned about the yellow warning signs.  I'm also concerned that most of them weren't needed in the first place and now we gotta replace 'em.  (fer crying out loud, maybe we should just take them down)

More when I have it. 

That's all for now.  Gotta go watch the Rangers win Game 3 of the ALCS.


P.S.  Please check out Paul Carlson's excellent RR FAQ's.  Paul is a leader in this field and has a very practical take on this.  He's been a great help to me in understanding what is and what ain't the requirements.

Robert Wunderlich P.E.
Sr. Managing Dir.- Transportation/Engineering
City of Garland
Garland TX

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Mike Spack

My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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