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Section 4: Flashing Operation

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All traffic signals are programmed to operate in the flash mode for emergencies. Signals may also operate in maintenance flash, railroad preemption flash, or scheduled operational flash modes.

The type of flash used (all-red or yellow-red) must be considered carefully. Driver expectation is an important factor. Drivers are conditioned to react to situations through their experiences. Mixing the types of flash can confuse drivers if they are accustomed to the all-red flash. The benefits of operating a mixed color flash must be weighed against the disadvantages. Violation of driver expectation can be a disadvantage of a mixed color flash.

Refer to the Texas Manual on Uniform Traffic Control Devices (TMUTCD) for specific instructions on flashing operations.

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Malfunction Flash

Malfunction flash mode is used when the conflict monitor senses a malfunction. Malfunction flash should use all-red flash exclusively.

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Maintenance Flash

Maintenance flash mode can be programmed for the operation of the intersection during routine maintenance. Yellow-red flash can be used if the main street traffic is significantly more than the minor street traffic.

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Railroad Preemption Flash

When a traffic signal is preempted by a train, flashing operation may be used while the train is going through the crossing. Either all-red flash or yellow-red flash can be used.

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Scheduled Flash

Traffic signals can operate in scheduled flash mode as a time-of-day operation (nighttime flash). Nighttime flash can reduce delay at intersections operating in the fixed time mode. Scheduled flash mode typically uses the yellow-red flash type operation. Nighttime flash should not be used at fully actuated intersections unless all other intersections in the area operate nighttime flash. Again, driver expectation is a major factor in this decision.

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Left-Turn Flash

When a traffic signal has left-turn signal heads the type of flash operation must be considered. If using an all-red flash operation, the left-turn signal heads should flash red. If using a yellow-red flash operation, the left-turn signal indication should flash red for both the yellow flash direction and the red flash direction.

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