What are the dimensions of a standard traffic light (stoplight) in North Carolina?

rstone1-ga:

The dimensions of all traffic lights in North Carolina are defined in
two publications, both linked from the NC Department of Transportation
website:

http://www.doh.dot.state.nc.us/preconstruct/traffic/

The two links are:

North Carolina Supplement to Manual on Uniform Traffic Control Devices (NCSMUTD)
http://www.doh.dot.state.nc.us/preconstruct/traffic/reports/NCSupplement.pdf

Manual on Uniform Traffic Control Devices (MUTCD) -   maintained by
the Federal Highway Administration
http://mutcd.fhwa.dot.gov/


In the NCSMUTCD, section 4D.15 (page 4-7) through section 4D.18 define
how all traffic control devices in N. Carolina are constructed and
erected. In particular:

------------------
"Section 4D.15 Size, Number, and Location of Signal Faces by Approach...

...Standard:
Three hundred millimeter (12 inch) signal lenses shall be used:
? On approaches where the design speed exceeds 56 km/hr (35 MPH).
? When signal faces are located more than 35 meters (120 feet) from the
stop line.
? For approaches to all signalized intersections for which the minimum
visibility distance in Table 4.1 of the MUTCD cannot be met.
? For all ARROW sections.
? At intersections with ramp terminals where traffic exits a superhighway
(freeway).

Guidance:
Three hundred millimeter (12 inch) signal lenses should be used in all
traffic signal heads.
The design speed for traffic signals should be considered as the
posted speed limit for an approach unless a speed study determines
that the 85th percentile speed is faster. If this is the case, the
85th percentile speed may be used.

Option:
Two hundred millimeter (8 inch) signal lenses may be used in traffic signal heads:
? On approaches where the design speed is 56 km/hr (35 MPH) or less.
? An engineering study indicates that extra visibility or target value is not
needed."
------------------

The 'Guidance' section is actually mirrored from the Federal Highway
Administration's MUTCD, directly linked here:

http://mutcd.fhwa.dot.gov/HTM/2003/part4/part4d.htm

The MUTCD does not define any standard dimensions for the traffic
light beyond the sizes of the lenses. These dimensions are covered by
another publication referenced by the FHA, in section 1A.11:

""Vehicle Traffic Control Signal Heads," Part 1?1985 Edition; Part
2?1998 Edition (ITE)"

This standard is not available for viewing online; it may be available
at your public library.

As traffic lights manufactured and sold in the United States must also
conform to these standards, you can find out the overall size of a
typical three-section traffic light by looking at the specifications
for a manufacturer's traffic light, such as the following:

http://www.idc-traffic.com/pdf/Alum8_12.pdf

In this specification, page 4 indicates that the height of a traffic
light section for an 8-inch lens is 10.25 inches, while the height for
a traffic light section with a 12-inch lens is 14 inches. Depending on
the number of sections, you can calculate the height of the lights.

The backplates for traffic lights also conform to standards, and are
available in 5" border and 8" border versions:

http://www.idc-traffic.com/pdf/backplts.pdf


I hope that this helps! If you would like me to clarify any part of
this Answer, please let me know using the Request Clarification button
above, before you rate and close this Question.

Regards,

aht-ga
Google Answers Researcher

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Request for Answer Clarification by rstone1-ga on 04 Mar 2004 17:13 PST

This is fantastic.  Can you clarify for me though exactly how many
inches in height a standard traffic light would be with 3 lights (red,
yellow, green)?

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Clarification of Answer by aht-ga on 04 Mar 2004 17:26 PST

You probably knew I was going to say "That Depends", didn't you? :)

Well, it really does depend on the size of the lights used. On a
typical city street, an 'older' traffic light with 8" lenses and a 5"
backplate is most likely used. This would be:

   Top of Backplate     5.00"         Side of backplate  5.00"
   Red Light           10.25"         
   Yellow Light        10.25"         Width of light    10.25"
   Green Light         10.25"
   Bottom of Backplate  5.00"         Side of backplate  5.00"
  -------------------- ------         ----------------- ------
   Total Height        40.75"         Total Width       20.25"

The actual dimension may be a bit different depending on how well the
actual traffic control device is assembled, but generally the total
height would be about 41".

Some newer city street traffic lights may use a 12" lens for the red
light, to make it more visible than the yellow or green. That would
add 3.75" to the total height, making it 44.50" or so.

If the light is on a faster road (like a highway), then all of the
lenses will be 12" lenses, and the backplate will be the one with the
8" border, making the whole assembly 58", or almost 5 feet tall!

Hope this helps,

aht-ga
Google Answers Researcher

Excellent, fast response.