Chapter 3: Traffic Studies

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Section 1: Overview

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Introduction

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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Responsibility

TxDOT is responsible for conducting traffic studies on numbered state routes, locations within incorporated 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 normally conduct traffic studies (as described in Sections 2 through 8 of this chapter). Traffic study information is then submitted to the district engineer for review and approval, as described in Section 8 of this chapter.

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Costs

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. Some of the data is difficult and time consuming to collect. Examples of the types of data typically collected are:

  • condition diagram (covered in Section 2 of this chapter)
  • location map (covered in Section 3 of this chapter)
  • photographs (covered in Section 3 of this chapter)
  • accident (crash) information (covered in Section 4 of this chapter)
  • vehicular and pedestrian traffic counts (covered in Section 5 of this chapter)
  • approach speeds (covered in Section 6 of this chapter)
  • Traffic Survey Count Analysis Form (covered in Section 7 of this chapter)
  • intersection delay study (covered in Section 8 of this chapter).

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

Research Report 3991‑2F (“Traffic Signal Warrants: Guidelines for Conducting a Traffic Signal Warrant Analysis,” sponsored by TxDOT in cooperation with US DOT and FHWA) suggests that the data for traffic studies should be collected in five phases, which are associated with the traffic signal warrants. 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

Warrants

Phase 1 — Volume Warrants

  • Warrant 1: Minimum Vehicle Volume
  • Warrant 2: Interruption of Continuous Traffic
  • Warrant 9: Four Hour Volumes
  • Warrant 11: Peak Hour Volume
  • Warrant 12: Warrant Volumes for Traffic Actuated Signals
  • Warrant 8: Combination of Warrants

Phase 2 — Accident Warrant

  • Warrant 6: Accident Experience

Phase 3 — Signal Operation Warrants

  • Warrant 5: Progressive Movement
  • Warrant 7: Systems

Phase 4 — Delay Warrant

  • Warrant 10: Peak Hour Delay

Phase 5 — Pedestrian Warrants

  • Warrant 4: School Crossing
  • Warrant 3: Minimum Pedestrian Volume.


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