№ 001B: 911 Address Sign

Making it easy for fire fighters and paramedics to find your house is very important, and because 911 porch light flashers are now very difficult to find, we need a reliable, low-tech method of helping them.

Enter the reflective house number sign. These use retroreflective sheeting applied to a metal base, with numbers also made from retroreflective sheeting applied on top, to reflect light back to the source (the headlights or spotlights of the fire engine or ambulance).

But there is not an official nationwide standard for emergency house number signs. Each municipality typically creates its own. I’m quite sure of this because of how much time I spent researching this. I spent hours googling and reading, and found only inconsitent local standards. I asked on Quora, and not one answer there could point to even a local standard. I called NENA and spoke to their expert in street address standards, and was told there indeed was no standard.

So we’re going to design the outline of one.

Retroreflective Sheeting

The development or retroreflective sheeting is fascinating, and in reading about it you will get a better understanding of the physics of light, and why selecting an address sign with the right material is important. The different grades of material reflect different amounts of light, and have different durability properties.

In order to choose the right type of sign, we need to look at three different standards:

  1. Retroreflective material
  2. National road sign standards
  3. Local address sign standards

Retroreflective material is the most technical standard among these, controlled by at least two different specifications:

  1. ASTM D4956 – 17, “Standard Specification for Retroreflective Sheeting for Traffic Control”. Interestingly, this document is the second non-metric item we have to put up with (the first was wood screws). ASTM D4956 states, “The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.”—but I’m not going to tilt at this windmill right now.
  2. AASHTO M268-13

These are specified in the 2014 Traffic Sign Retroreflective Sheeting Identification Guide, published by the U.S. Federal Highway Administration. These documents specify classes of material in Roman numerals:

  • Type Ⅰ is “engineer grade” and offers only 28% reflectivity; not good enough.
  • Type Ⅱ is “super engineer grade” and is somewhat better, but still not good enough.
  • Type Ⅲ is “high intensity” and the minimum you want to use, because Type Ⅰ and Ⅱ do “not meet minimum AASHTO classification criteria” according to the U.S. Department of Transportation.
  • Type Ⅳ is “high intensity” or brand-specific names such as “Diamond Grade LDP”.
  • Type Ⅷ has brand names such as “Crystal Grade” and “MVP Prismatic”.
  • Type Ⅸ has brand names such as “Diamond Grade VIP”.
  • Type Ⅺ has brand names such as “Diamond Grade” and “DG3 OmniCube”.

Manual on Uniform Traffic Control Devices

The full name is actually “Manual on Uniform Traffic Control Devices for Streets and Highways” (U.S. DOT official page), but everyone in the civil engineering industry just calls it MUTCD (Wikipedia article).

The standard color for street name signs in the MUTCD is white letters on green background, but it also allows a few other color combinations:

The only acceptable alternative background colors for Street Name (D3-1 or D3-1a) signs shall be blue, brown, or white. Regardless of whether green, blue, or brown is used as the background color for Street Name (D3-1 or D3-1a) signs, the legend (and border, if used) shall be white. For Street Name signs that use a white background, the legend (and border, if used) shall be black.

I recommend sticking with white numbers on a green background, but if you must choose one of the other colors, white on blue is the next most visible combination.

For number height, we look to this statement in the MUTCD:

On low-volume roads and on urban streets with speeds of 25 mph (40 km/h), the principal legend shall be in letters at least 4 inches (100 mm) high.

Thank god for them including metric values! Now we can use the nice standard size of 100 millimeters as our number height (even though it’s a few millimeters short of 4 inches).

Local Standards

Before you go buy a commercial sign, check with your city or fire department. Some of them indeed have standards for emergency house number signs, a preferred vendor, and a discounted price (a few are even free). I’ve seen one municipality specify two different colors for different building construction types (white numbers on a red background for lightweight construction using engineered wood beams instead of 2x4s), because it dramatically affects how quickly the house will burn and how the firefighters attack the fire.

DIY Standard

If your city or fire department doesn’t offer a similar service, then use these rules to choose your sign:

  • 2 mm-thick (14 gauge) metal sign made of aluminum covered by ASTM D4956 Type Ⅲ or better retroreflective sheet, 150 millimeters wide, by however tall needed for the numbers. Yep; you’re going to mount the sign vertically.
  • A metal or wood post (if you don’t have a conventional mailbox post) to hold the top of the sign 1 meter above the front lawn, yard, driveway, etc.
  • Retroreflective numbers 100 millimeters tall, on both sides of the sign, since you can’t predict from which direction the fire engine will come.
  • Preferably custom-order the sign so that the numbers are applied straight and even, and under controlled conditions so they won’t peel off. The one product I can find on Amazon is the Green and White Mailbox Sign from Night Vision Signs.
  • If you really prefer to buy a blank sign and affix the numbers yourself, go ahead, but just realize that most all of the signs I’ve seen only have three of each digit. If you’ve got even two of the same digit in your address, you won’t be able to put the numbers on both sides of the sign.

The next post will cover all the complexities of dialing 911. What was supposed to be a simple and reliable way to be connected to your closest emergency dispatch center is now all buggered up.

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