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Section 2: Coordinated Operation

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Introduction

Traffic signals can operate at an independent intersection or as part of a coordinated system. The traffic signals can be set up to operate in the fully actuated mode, in fixed time mode, or in a flashing mode of operation. How a signal is operated determines its effectiveness in reducing delay and increasing safety. Signal operation also influences public acceptance.

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Coordinating Operations with Other Jurisdictions

The operation of TxDOT traffic signals often crosses jurisdictional boundaries. For this reason, it is often necessary to connect or operate TxDOT traffic signals with signals and control devices maintained and operated by other jurisdictions.

Agreements. If coordination across jurisdictional boundaries is accomplished by synchronizing time clocks (time-based coordination), then no agreement is necessary. If the coordination involves one jurisdiction operating (setting the timing) or maintaining (opening a cabinet for maintenance purposes), then a formal agreement between the entities is required. For information on agreements, see Chapter 16, “Traffic Engineering Agreements,” of the Contract Management Manual.

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Advantages of Coordinated Operation

Traffic signal systems are designed to minimize delay. An individual intersection operates most efficiently when it is allowed to respond to traffic demand in a fully actuated mode. Fully actuated operation allows the traffic signal to adjust the cycle length and phase split times on a cycle-by-cycle basis.

At all intersections, vehicles tend to group into “platoons.” Once a platoon is established, delay can be reduced by keeping the platoon moving through adjacent signals. The coordination of traffic signals (operating more than one signal in a system) can provide smooth progression along an arterial.

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Drawbacks of Coordinated Operation

Operating traffic signals in a coordinated mode does have some drawbacks. The coordination of the system may further delay some minor traffic movements.

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Determining Effectiveness of a Coordinated Operation

Several factors determine how effective a coordinated traffic signal system can be. These factors should be considered when determining if a signal should be operated independently in a fully actuated mode or as part of an arterial system. These factors include:

  • distance between intersections
  • system design speed and posted speed
  • required cycle length
  • required pedestrian phases.
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