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UIA Manual on Uniform Traffic Control Devices

UIA MUTCD — 1st Edition Based on the US MUTCD, 11th Edition, Revision 1 (December 2025) Published by the Alto Department of Transportation

The UIA Manual on Uniform Traffic Control Devices (UIA MUTCD) is the standard for all traffic control devices installed on any street, highway, causeway, bikeway, or private road open to public travel within the United Islands of Alto. It governs signs, signals, pavement markings, work zone traffic control, and every other device used to regulate, warn, or guide traffic.

Adoption​

The UIA MUTCD adopts the United States Manual on Uniform Traffic Control Devices, 11th Edition, Revision 1, dated December 2025, in its entirety, except as specifically amended by the addenda published below.

Where this manual is silent, the US MUTCD governs. Where an addendum in this manual conflicts with the US MUTCD, the addendum governs within the United Islands of Alto.

This is deliberate. The US MUTCD represents decades of human-factors research, crash analysis, and field experience that the UIA has no reason to duplicate and no ability to improve upon wholesale. Adopting it by reference — rather than rewriting it — means Alto inherits that work in full, and confines its own rulemaking to the specific practices where the UIA has chosen to diverge.

How to use this manual​

Read the US MUTCD as the base document. Before applying any section of Part 4 (Highway Traffic Signals), check the addendum register below to see whether that section has been amended for the UIA. Addenda are numbered by the federal chapter they modify, so an addendum affecting Section 4F.01 is numbered in the 4F- series.

Each addendum states the federal section it modifies, quotes the federal text being changed, and gives the UIA text that replaces or supplements it.

Applicability​

FacilityGoverning manual
City of Alto streets and local roadsUIA MUTCD
Federal routes and inter-island causewaysUIA MUTCD, plus UIAHA supplemental standards
Private roads open to public travelUIA MUTCD
Private property not open to public travelNot regulated

Addendum Register​

AddendumSubjectModifiesStatusAdopted
4E-AStrobe-Equipped Signal IndicationsUS MUTCD 4E.01 ¶03, ¶04Adopted2026
4F-AStraight-Through Arrow Signal IndicationsUS MUTCD 4F.01 ¶09Adopted2026

Additional addenda are added to this register as they are adopted. An addendum number is never reused, and a withdrawn addendum remains listed with a status of Withdrawn so that older plan sets can still be interpreted.

Addendum 4E-A — Strobe-Equipped Signal Indications​

Modifies: US MUTCD Section 4E.01, Paragraphs 03 and 04 Related federal sections: 4E.01 ¶10 (ITE equipment standards), 4G.01 ¶01–02 (flash rate), 4S.01 ¶03 (beacon flash rate) Status: Adopted

Federal provision being amended​

US MUTCD Section 4E.01, Paragraph 03 (Standard) reads:

Strobes shall not be used within or adjacent to any signal indication.

Paragraph 04 (Standard) further provides that, except for expressly permitted flashing indications and emergency-vehicle preemption displays, flashing displays shall not be used within or adjacent to any signal indication.

The federal position on strobe devices at signalized locations was set out in FHWA Interpretation Letter 4-311(I), issued August 23, 2006, which concluded that strobe-type light bars did not conform to the signal head equipment standards then referenced, and did not meet the required flash rate for flashing indications. That interpretation cited the section numbering of the edition in effect at the time; the equivalent provisions in the 11th Edition are those listed above.

UIA amendment​

Paragraphs 03 and 04 of Section 4E.01 are amended to read as follows within the United Islands of Alto:

03 (UIA) A strobe may be used within a signal indication in accordance with UIA MUTCD Addendum 4E-A. Strobes shall not be used adjacent to any signal indication.

04 (UIA) Except for flashing vehicular and pedestrian signal indications, the distinctive indications for emergency-vehicle preemption, and strobe-equipped signal indications conforming to Addendum 4E-A, flashing displays shall not be used within or adjacent to any signal indication.

The federal rule prohibits strobes in both positions. This addendum splits them: the strobe moves inside the indication, where it is permitted, and remains prohibited outside it.

Placement​

Three signal faces. A strobe within a circular red indication and a strobe within a straight-through red arrow are both permitted; an external strobe bar mounted adjacent to the signal face is prohibited.

Figure 4E-A-1. A strobe is permitted within a red signal indication. A separate strobe device mounted adjacent to the signal face remains prohibited under Section 4E.01 ¶03 as amended.

Provisions​

Standard:

  1. A strobe shall be incorporated only within a steady CIRCULAR RED or straight-through RED ARROW signal indication. A strobe shall not be incorporated within any yellow or green signal indication, within a turn arrow indication, or within a pedestrian or bicycle signal indication.
  2. A strobe-equipped signal indication shall flash only while the red indication in which it is incorporated is displayed. It shall not flash during the yellow change interval, during any green interval, or while the signal is in flashing operation.
  3. A strobe shall not alter the color, shape, size, or apparent position of the signal indication in which it is incorporated. With the strobe not flashing, the indication shall be a conforming red signal indication in all respects.
  4. Not more than one signal indication in any signal face shall be strobe-equipped.
  5. Strobes shall not be mounted adjacent to, above, below, or beside any signal face. External strobe bars, light bars, and discrete strobe units paired with a signal indication are prohibited.
  6. A strobe-equipped signal indication shall be equipped with automatic dimming that reduces output during nighttime conditions.
  7. Strobe-equipped signal indications shall not be used at more than one signalized location within any 500 feet of continuous roadway on the same approach.

Guidance:

  1. A strobe-equipped signal indication should be installed only where an engineering study has identified a visibility or expectancy problem that conventional measures — signal head size, additional signal faces, visibility-limited faces, advance warning signs, or lighting — have not resolved.
  2. Flash rate should be selected for conspicuity rather than for conformance with the 50 to 60 flashes per minute range required of flashing signal indications by Section 4G.01. A rate distinctly outside that range is preferred, so that a strobe-equipped red indication is not mistaken for a flashing red indication requiring a stop-and-proceed movement.
  3. Strobe-equipped signal indications should be used sparingly. An approach on which every signal carries one conveys no more information than an approach on which none does.

Option:

  1. A strobe may be incorporated within a straight-through RED ARROW signal indication on a signal face conforming to Addendum 4F-A.

Support:

  1. The UIA's position is that a strobe belongs inside the indication it reinforces. A driver reading a strobe-equipped red sees one device with one meaning — stop — rendered more conspicuously. A separate strobe mounted beside the signal head is a second device with no defined meaning, which the driver must interpret and associate with the correct signal face; that association is exactly what fails at a complex or unfamiliar intersection. The federal manual resolves this by prohibiting both. The UIA resolves it by permitting the integrated form and prohibiting the separate one.

Addendum 4F-A — Straight-Through Arrow Signal Indications​

Modifies: US MUTCD Section 4F.01, Paragraph 09 Related federal sections: 4E.01 ¶09.A (arrow direction), 4F.01 ¶03.B.1 (circular yellow following a through green arrow), 4F.01 ¶05 (through green arrow as an option), 4F.01 ¶10.C (prohibited simultaneous displays) Status: Adopted

Federal provision being amended​

US MUTCD Section 4F.01, Paragraph 09 (Standard) reads:

A straight-through RED ARROW signal indication or a straight-through YELLOW ARROW signal indication shall not be displayed on any signal face, either alone or in combination with any other signal indication.

Under the federal manual, a straight-through GREEN ARROW is permitted — Section 4F.01 ¶05 allows one in place of a CIRCULAR GREEN to discourage wrong-way turns — but the through movement must be terminated by a CIRCULAR YELLOW and prohibited by a CIRCULAR RED. The result is a signal face that speaks in arrows on green and in circles on yellow and red.

UIA amendment​

Paragraph 09 of Section 4F.01 is deleted and replaced with the following within the United Islands of Alto:

09 (UIA) A straight-through RED ARROW signal indication or a straight-through YELLOW ARROW signal indication may be displayed on a signal face in accordance with UIA MUTCD Addendum 4F-A.

Section 4F.01 ¶03.B.1 is amended to permit a straight-through YELLOW ARROW signal indication, in place of a CIRCULAR YELLOW, following a straight-through GREEN ARROW signal indication in the same signal face.

Section 4F.01 ¶10.C is amended to read: a straight-through GREEN ARROW shall not be displayed simultaneously with a CIRCULAR RED or a straight-through RED ARROW on the same signal face.

Comparison with federal practice​

Two three-section signal faces compared. Under federal practice the face shows a circular red, circular yellow and a green up-arrow. Under UIA Addendum 4F-A all three indications are up-arrows.

Figure 4F-A-1. Federal practice permits a straight-through GREEN ARROW but requires circular indications for the change and stop displays. Addendum 4F-A permits the whole face to be shown in arrows.

Provisions​

Standard:

  1. Where a signal face displays a straight-through GREEN ARROW signal indication, that face may display a straight-through YELLOW ARROW and a straight-through RED ARROW for the change and stop indications respectively.
  2. A signal face using straight-through arrow indications shall use arrow indications for all three of its through-movement displays. A face shall not mix a straight-through GREEN ARROW with a CIRCULAR YELLOW or CIRCULAR RED, or any other partial combination.
  3. A straight-through RED ARROW signal indication shall have the same meaning as a CIRCULAR RED signal indication, except that it prohibits only the through movement. Turning movements from the same approach shall be controlled by their own signal faces.
  4. Straight-through arrow indications shall point vertically upward, in accordance with Section 4E.01 ¶09.A.
  5. All straight-through arrow signal indications shall be 12 inches nominal, in accordance with Section 4E.02 ¶03.
  6. Where a straight-through RED ARROW is displayed, a right turn on red or left turn on red from that approach shall be permitted or prohibited by the signal face controlling that turning movement, and not by the through-movement face.

Guidance:

  1. Straight-through arrow signal faces should be used where the through movement is controlled separately from turning movements and where displaying the through movement in arrows improves clarity — most commonly on approaches with a separate through-only lane group, at intersections with unusual geometry, or where wrong-way turn risk exists.
  2. Straight-through arrow signal faces should not be used on an approach where all movements are controlled by a single shared signal face.
  3. Because straight-through red and yellow arrows are not used under federal practice, agencies should consider whether a location's traffic includes a substantial proportion of drivers unfamiliar with UIA practice before installing them.

Support:

  1. The federal prohibition rests on uniformity: a driver anywhere in the United States can expect the stop indication to be circular. The UIA has accepted a narrower uniformity — arrows control arrows, circles control everything — on the view that a movement-specific red is clearer at intersections where movements are separately signalized, and that the through-arrow convention is internally consistent once applied to a whole signal face.
  2. This addendum does not change the meaning of any indication. A straight-through RED ARROW means stop, exactly as a CIRCULAR RED does.

Amendment Process​

Amendments to the UIA MUTCD are proposed to the Standards & Design Division, reviewed by the Transportation Commission, and adopted by the Director of Transportation.

A proposal must state the federal section affected, the text proposed, the operational or safety problem the change addresses, and why the existing provision is inadequate. Proposals that would create a device with no federal counterpart carry a higher burden: the proponent must show the device is unambiguous to a driver who has never seen it before.

Adopted addenda take effect on publication in the register above. Existing installations that conform to the previous provision are not required to be replaced unless the addendum says so.

Interim Approvals and Experimentation​

The UIA does not currently operate an experimentation program. Devices not covered by the US MUTCD or by an addendum in this manual shall not be installed on any facility open to public travel in the United Islands of Alto.

Requests to experiment are handled case by case through the amendment process above.

References​

The United Islands of Alto is a virtual jurisdiction. This manual is published for thematic purposes and carries no legal authority. See the site disclaimer.