I remember reading at one point that all phases of a traffic signal must be 12" these days. Is that true? I ask, because I was in Portland, OR a few weeks ago, and found that they were installing mixed size signals near the new Tillikum Crossing, and found them quite odd.
I'm assuming that mixture you're referring to is 12-8-8 for R-Y-G. When I was last in Salem, OR a few years ago (2009); I saw some fairly-new signal installations that featured 12-8-8 signal heads.
2009 MUTCD Section 4D.07:
02 Except as provided in Paragraph 3 below, 12-inch signal indications shall be used for all signal sections in all new signal faces.
Option:
03 Eight-inch circular signal indications may be used in new signal faces only for:
The green or flashing yellow signal indications in an emergency-vehicle traffic control signal (see Section 4G.02);
The circular indications in signal faces controlling the approach to the downstream location where two adjacent signalized locations are close to each other and it is not practical because of factors such as high approach speeds, horizontal or vertical curves, or other geometric factors to install visibility-limited signal faces for the downstream approach;
The circular indications in a signal face that is located less than 120 feet from the stop line on a roadway with a posted or statutory speed limit of 30 mph or less;
The circular indications in a supplemental near-side signal face:
The circular indications in a supplemental signal face installed for the sole purpose of controlling pedestrian movements (see Section 4D.03) rather than vehicular movements; and
The circular indications in a signal face installed for the sole purpose of controlling a bikeway or a bicycle movement.
04 Existing 8-inch circular signal indications that are not included in Items A through F in Paragraph 3 may be retained for the remainder of their useful service life.
No, not necessarily.
12" traffic signals are required to be installed on roads that have speed limits above 30 M.P.H., while 8" heads are adequate for roads with speed limits below that number. These stem primarily to visibility purposes.
The city of New York, as an example, is one municipality that still continues to heavily install 8" traffic signals. Though, where necessary, 12" heads are in use there as well.
Quote from: Big John on December 07, 2014, 07:56:07 PM
2009 MUTCD Section 4D.07:
02 Except as provided in Paragraph 3 below, 12-inch signal indications shall be used for all signal sections in all new signal faces.
Option:
03 Eight-inch circular signal indications may be used in new signal faces only for:
The green or flashing yellow signal indications in an emergency-vehicle traffic control signal (see Section 4G.02);
The circular indications in signal faces controlling the approach to the downstream location where two adjacent signalized locations are close to each other and it is not practical because of factors such as high approach speeds, horizontal or vertical curves, or other geometric factors to install visibility-limited signal faces for the downstream approach;
The circular indications in a signal face that is located less than 120 feet from the stop line on a roadway with a posted or statutory speed limit of 30 mph or less;
The circular indications in a supplemental near-side signal face:
The circular indications in a supplemental signal face installed for the sole purpose of controlling pedestrian movements (see Section 4D.03) rather than vehicular movements; and
The circular indications in a signal face installed for the sole purpose of controlling a bikeway or a bicycle movement.
04 Existing 8-inch circular signal indications that are not included in Items A through F in Paragraph 3 may be retained for the remainder of their useful service life.
That was what I needed. I recall the speed limit in this area to be 30, so that makes sense. And given that Portland largely has mixed size signals, they probably wanted to keep the continuity.