Chapter 3: Traffic Studies

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Section 1: Overview

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A traffic study consists of a comprehensive investigation of existing physical and operating conditions. Analysis of the study data provides insight into possible remedial measures, if any. Remedial measures may include various traffic control measures, such as speed zoning, channelization, signing, traffic signals, safety lighting, or a combination of these. This chapter pertains only to traffic studies which may result in the installation of traffic signals.

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TxDOT is responsible for conducting traffic studies on numbered state routes, locations within incorporated cities with populations less than 50,000, and on interstate frontage roads. Incorporated cities with populations greater than 50,000 should conduct their own traffic studies.

Districts should conduct traffic studies (as described throughout this chapter) and submit them to the district engineer for review and approval.

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Normally the costs for conducting traffic studies are absorbed into the operations of the districts. However, traffic study costs for federal-aid projects are reimbursable by the Federal Highway Administration (FHWA) if a control section job number has been assigned by the Transportation Planning and Programming Division (TPP).

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Required Information

A complete traffic study for a proposed traffic signal or flashing beacon installation requires the collection of sufficient data on the physical, traffic, and operational characteristics of the intersection. Examples of the types of data typically collected are:

When the traffic signal study is complete, the information is tabulated and checked against the traffic signal warrants set forth in the Texas Manual on Uniform Traffic Control Devices (TMUTCD). The district traffic section supervisor then makes a recommendation to the district engineer using the Traffic Signal Authorization Request form (as described in Chapter 5 of this manual).

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Warrant Analysis Data

It is common to first analyze warrants requiring data that is easier to collect. If a signal does not meet any of these warrants, then the more difficult data is collected and the other warrants are analyzed. The following table shows the suggested phased data collection and associated warrants.

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Phase 1 — Volume Warrants

  • Warrant 1: Eight Hour Vehicular Volume
  • Warrant 2: Four Hour
  • Warrant 3: Peak Hour

Phase 2 — Crash Warrant

  • Warrant 7: Crash Experience

Phase 3 — Signal Operation Warrants

  • Warrant 6: Coordinated Signal System
  • Warrant 8: Roadway Network

Phase 4 — Railroad Warrants

  • Warrant 9: Intersection Near a Grade Crossing

Phase 5 — Pedestrian Warrants

  • Warrant 4: Pedestrian Volume
  • Warrant 5: School Crossing.

In addition to meeting the minimum criteria for one or more of these warrants, an engineering study must also indicate that installing a traffic signal would improve the safety and/or operation of the intersection without disrupting the progressive flow of traffic. Simply meeting a warrant does not necessitate the installation of a traffic signal.

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Recommending Against Installation

When the district's traffic study indicates that a traffic signal is not needed, the district should notify the requesting party, by letter, that a traffic signal installation is not recommended. In unusual cases, the district may wish to submit their traffic study to TRF for review and comment prior to notifying the requesting party of the study results.

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