3.4 Coordinated, Crash Experience, Grade Crossing, and PHB Warrants (Warrants 6, 7, and 9)

3.4 Coordinated, Crash Experience, Grade Crossing, and PHB Warrants (Warrants 6, 7, and 9)

[!IMPORTANT] Specialized Systemic & Safety Warrants: Warrants 6, 7, and 9 address operational challenges beyond baseline vehicular and pedestrian volumes. Warrant 6 (Coordinated Signal System) maintains arterial progression; Warrant 7 (Crash Experience) addresses persistent angle crash histories; and Warrant 9 (Grade Crossing) mitigates catastrophic railroad queue entrapment risks. Additionally, Pedestrian Hybrid Beacons (PHBs) provide a targeted alternative for midblock pedestrian safety.

For senior field technicians and signal systems engineers, these specialized warrants represent critical intersections between electrical cabinet architecture, preemption priority, corridor progression timing, and system safety.

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Warrant 6: Coordinated Signal System

MUTCD Section 4C.07 establishes Warrant 6 (Coordinated Signal System). Progressive movement in a coordinated signal system frequently demands that adjacent signals be spaced at specific intervals to maintain vehicle platoons. Installing a signal under Warrant 6 is justified when:

1. On a one-way street or a street with predominantly unidirectional flow, adjacent signals are spaced too far apart to maintain platooning and enforce speed progression; OR
2. On a two-way street, adjacent signals do not provide the necessary degree of platoon control, and the proposed signal will enhance progressive vehicular flow without disrupting existing progression.

Spacing Limitation Rule

[!WARNING] Minimum Spacing Guideline: A traffic control signal justified under Warrant 6 should not be installed if the resulting signal spacing would be less than 1,000 feet (300 meters or ~0.2 miles) to adjacent signals. Spacing signals closer than 1,000 feet severely degrades progression, causes vehicle queue spillbacks into upstream intersections, increases fuel consumption, and elevates rear-end collision rates.

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Warrant 7: Crash Experience

MUTCD Section 4C.08 defines Warrant 7 (Crash Experience), which is applied where severe collision histories are the primary justification for signalization.

The Three-Part Test (11th Edition)

[!WARNING] Retired criterion alert. Legacy training material states that Warrant 7 needs "five or more reported crashes of types susceptible to correction within a 12-month period." The 11th Edition deleted that rule and replaced it with threshold tables derived from Highway Safety Manual safety performance functions. Answer from Tables 4C-2 through 4C-5, not from the old five-crash number.

Under Section 4C.08, Paragraph 2, all three of the following must be met:

+--------------------------------------------------------------------------------+
|              Warrant 7 (Crash Experience) - MUTCD 11th Edition                  |
+--------------------------------------------------------------------------------+
| A. Failed Trial of Alternatives:                                               |
|    Adequate trial of alternatives with satisfactory observance and             |
|    enforcement has failed to reduce the crash frequency.                       |
|                                                                                |
| B. Crash Threshold - ANY ONE of four table comparisons:                        |
|    1. Angle + pedestrian crashes (all severities), 1-year  -> Table 4C-2       |
|    2. Fatal-and-injury angle + pedestrian crashes, 1-year  -> Table 4C-2       |
|    3. Angle + pedestrian crashes (all severities), 3-year  -> Table 4C-3       |
|    4. Fatal-and-injury angle + pedestrian crashes, 3-year  -> Table 4C-3       |
|                                                                                |
| C. Volume Floor:                                                               |
|    For each of any 8 hours, the 80% columns of Condition A OR the 80%          |
|    columns of Condition B in Table 4C-1, OR pedestrian volume at least         |
|    80% of the Warrant 4 (Pedestrian Volume) requirement.                       |
+--------------------------------------------------------------------------------+

Crash Threshold Tables

An angle crash is defined in the table footnotes as any crash occurring at an angle that involves one or more vehicles on the major street and one or more on the minor street. Pedestrian crashes are counted with them.

In Tables 4C-2 and 4C-3 the threshold is the same for every lane configuration; only the number of intersection legs changes the number.

The Reduced-Condition Tables (4C-4 and 4C-5)

Under Paragraph 5, if the posted or statutory speed limit or the 85th-percentile speed on the major street exceeds 40 mph, or the intersection lies in the built-up area of an isolated community of fewer than 10,000 people, then the 56% columns of Table 4C-1 may replace the 80% columns and Tables 4C-4 and 4C-5 may replace Tables 4C-2 and 4C-3. Note the counter-intuitive result — for multi-lane approaches the reduced-condition thresholds are higher, not lower:

Agency-Specific Safety Performance Functions

Paragraph 6 permits agencies to calibrate Highway Safety Manual safety performance functions to their own crash data, or develop their own, and to use the resulting agency-specific crash frequency values instead of Tables 4C-2 through 4C-5 when the derivation is documented as part of the engineering study.

Documenting Less Restrictive Alternatives

Technicians must verify that the operating agency has attempted non-signal remedial treatments, including:

• Installing oversized, fluorescent retroreflective STOP signs (R1-1) and high-visibility retroreflective post strips.
• Installing advance warning signs with flashing yellow warning beacons (STOP AHEAD W3-1).
• Clearing physical sight obstructions within the intersection sight triangles.
• Installing dynamic blank-out warning signs (TRAFFIC CROSSING DOES NOT STOP).
• Geometric channelization, such as offset left-turn bays, raised curb splitters, or conversion to a modern roundabout.

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Warrant 9: Intersection Near a Highway-Rail Grade Crossing

MUTCD Section 4C.10 establishes Warrant 9 (Intersection Near a Highway-Rail Grade Crossing). This warrant addresses severe hazards where an intersection approach is adjacent to a railway crossing, and traffic queues from the intersection stop line can back up across the railroad tracks, trapping vehicles in the path of approaching trains.

Physical Distance Prerequisite

Warrant 9 applies when a highway-rail grade crossing equipped with active warning devices (flashing lights and automatic gates) is located on an approach controlled by a STOP or YIELD sign, and the distance between the intersection stop line and the nearest track rail is within 140 feet (43 meters).

Volume Curves and Train Volume Adjustments

Warrant 9 evaluates hourly vehicular volume plotted on Figure 4C-9 or Figure 4C-10. The choice between them is governed by approach geometry, not speed: Section 4C.10, Paragraph 4 directs that Figure 4C-9 be used where only one lane approaches the highway-highway intersection at the track crossing location, and Figure 4C-10 where two or more lanes do. Each figure carries a family of curves selected by the clear storage distance $D$ defined in Section 1C.02:

• The x-axis represents the Major-Street Total Volume (both approaches combined, vph).
• The y-axis represents the Minor-Street Approach Volume Crossing the Tracks (one direction only, vph).
• Train Volume Multiplier ($H_t$): The minor-street approach volume is multiplied by an adjustment factor based on the number of passenger and freight trains operating across the grade crossing per day. Higher daily train volumes reduce the vehicular volume required to satisfy the warrant.

Preemption Architecture

When a signal is justified under Warrant 9, the signal system must be interconnected with the railroad crossing active warning system via a failsafe electrical preemption circuit (IEEE 1570 standard). Upon train detection, the traffic controller enters Railroad Preemption (Priority 1):

1. Terminates conflicting vehicular and pedestrian phases.
2. Displays a special Track Clearance Green Phase to immediately flush vehicles queued between the stop line and the tracks.
3. Holds conflicting movements in all-red dwell while the train traverses the grade crossing.

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Pedestrian Hybrid Beacons (PHBs / HAWKs)

MUTCD Chapter 4J defines standards for Pedestrian Hybrid Beacons (PHBs), formerly known as HAWK (High-Intensity Activated crossWalK) beacons. A PHB is an actuated beacon system used to assist pedestrians crossing a street at an unsignalized location where full Warrant 4 is not satisfied or where a full traffic signal is undesirable.

PHB Signal Head Face Arrangement

A vehicular PHB signal face consists of three signal sections arranged in an inverted triangle:

• Two Circular RED sections positioned horizontally on top.
• One Circular YELLOW section centered below the red sections.

PHB Six-Stage Indication Sequence

Upon pedestrian actuation of the ADA pushbutton, the PHB executes a unique six-stage operational sequence:

[1. Resting: DARK]  ───>  [2. Flashing YELLOW]  ───>  [3. Steady YELLOW]
       ^                                                       │
       │                                                       v
[6. Back to DARK]   <───  [5. Alternating Red]   <───  [4. Steady RED]
                          (Wig-Wag: Stop & Go)        (Solid Stop / WALK)

1. Resting State (Vehicular: DARK / Pedestrian: Steady UPRAISED HAND): The beacon remains unlit to vehicular traffic, allowing free-flowing traffic without artificial delay. Pedestrian heads display a solid UPRAISED HAND (Don't Walk).
2. Pedestrian Actuation (Vehicular: FLASHING YELLOW / Pedestrian: Steady UPRAISED HAND): Pushbutton actuation triggers a flashing circular yellow indication for a few seconds, alerting approaching drivers that a pedestrian is waiting to cross.
3. Vehicular Clearance (Vehicular: STEADY YELLOW / Pedestrian: Steady UPRAISED HAND): Displays a steady circular yellow indication (3.0 to 5.0 seconds). Drivers must stop if safe to do so, identical to a standard signal yellow change interval.
4. Pedestrian Crossing Interval (Vehicular: STEADY RED / Pedestrian: WALKING PERSON): Displays two steady circular red indications horizontally. All approaching vehicles must come to a complete stop at the stop line. Pedestrian heads display the illuminated WALKING PERSON symbol.
5. Pedestrian Clearance Interval (Vehicular: ALTERNATING FLASHING RED / Pedestrian: Flashing UPRAISED HAND with Countdown): The two red indications flash alternately in a wig-wag pattern. Approaching drivers must come to a complete stop, but after stopping, drivers may proceed through the crosswalk if it is clear of pedestrians, operating like a STOP sign. Pedestrians receive the flashing UPRAISED HAND with numerical countdown.
6. Sequence Termination (Vehicular: DARK / Pedestrian: Steady UPRAISED HAND): Display returns to DARK for vehicular traffic and solid UPRAISED HAND for pedestrians.

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Summary of Warrants 6, 7, 9, and PHB Operations