Section 1: Overview
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.
Responsibility
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.
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).
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:
- condition diagram (covered in Chapter 3, Section 2)
- location map (covered in Chapter 3, Section 3)
- photographs (covered in Chapter 3, Section 3)
- crash data (covered in Chapter 3, Section 4)
- vehicular and pedestrian traffic counts (covered in Chapter 3, Section 5)
- approach speeds (covered in Chapter 3, Section 6)
- Traffic Survey Count Analysis Form (covered in Chapter 3, Section 7)
- intersection delay study (covered in Chapter 3, Section 8).
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).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.
Phase | Warrants |
|---|---|
Phase 1 — Volume Warrants |
|
Phase 2 — Crash Warrant |
|
Phase 3 — Signal Operation Warrants |
|
Phase 4 — Railroad Warrants |
|
Phase 5 — Pedestrian Warrants |
|
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.
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.