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Section 5: Operational Design

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Overview

Operational design involves subsections of Illumination, Intelligent Transportation Systems, Signals, and Signing/Striping. Construction plans result from each of the tasks within this section. This section includes the following groups of tasks. The tasks may be performed concurrently.

  • Illumination

5380. Design illumination

  • Intelligent Transportation System

5400. Design Intelligent Transportation System

  • Signals

5420. Design signalization plan

  • Signing and Striping

5440. Design signing and pavement markings

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Illumination

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5380: Design illumination

Description. There are two types of roadway lighting: continuous lighting and safety lighting. Safety lighting is typically needed at interchanges, high-volume rural or suburban intersections, weigh stations, and rest areas. Continuous lighting provides uniform lighting on all main lanes, ramps, direct connectors, and interchanges. Continuous lighting requires the financial participation of the city. Either type may use conventional roadway lighting or high mast poles.

Technical assistance with design is available from the Traffic Operations Division.

Determination of the eligibility of the project for illumination and compliance with warranting conditions should have been initiated when preliminary illumination locations were established in Task 2660.

For illumination structures taller than 200 feet (61 m) or closer than 20,000 feet (6,096 m) to an airport runway, or closer than 5,000 feet or (1,524 m) to a heliport, an FAA form 7460-1 must be completed. Refer to the FAA website for more detailed information and to submit the proper form. Safety lighting is typically needed at interchanges, high-volume rural or suburban intersections, weigh stations, and rest areas.

Pertinent Project Types. Projects warranting continuous roadway lighting or safety lighting.

Responsible Party. Designer with illumination experience.

Sub-tasks.

  • Obtain agreement with local government for maintenance of proposed continuous lighting.
  • Obtain preliminary roadway, drainage, traffic, and utility adjustment plans.
  • Obtain design year traffic data.
  • Make a site visit to inspect existing conditions.
  • Obtain or prepare a lighting justification report.
  • Design high mast foundations according to bore logs and HMIF standard sheets.
  • Coordinate plans with roadway design, traffic, and structural engineers.

Helpful Suggestions.

  • Know the project requirements for horizontal clearance to obstructions (clear zone). Use breakaway devices according to Highway Illumination Manual and AASHTO requirements.
  • Find out where traffic barrier will be located, and try to place hazardous objects behind or on barriers that are already proposed for other purposes.
  • Determine the locations of existing and proposed utilities, drainage facilities, and traffic signs and signals.
  • Consider maintenance requirements when locating illumination supports.
  • For lighting on bridges, coordinate design illumination with bridge details so conduit is made part of bridge plans; this will avoid unsightly conduit additions to bridges.
  • Determine illuminance design values according to roadway classification and AASHTO Roadway Lighting Design Guide.
  • Texas is required by Health and Safety Code Chapter 425 to use cutoff fixtures when installing lighting using state funds to minimize glare and light pollution.
  • When designing lighting for a sidewalk adjacent to a roadway, the street must be lit to the same level as the sidewalk.

Authority Requirements.

Resource Material.

  • TxDOT Highway Illumination Manual
  • AASHTO Roadway Lighting Design Guide
  • NFPA 70:National Electric Code
  • ANSI/IESNA RP-8, Roadway Lighting
  • TxDOT PS&E Preparation Manual
  • TxDOT Bridge Design Manual
  • Federal Aviation Administration website at http://www.oeaaa.faa.gov for forms and instructions.
  • TxDOT Standard Sheets: Roadway Illumination Details (RID); Roadway Illumination Poles (RIP); High Mast Illumination Details (HMID); Electrical Details (ED); High Mast Illumination Pole (HMIP); High Mast Illumination Foundation (HMIF).
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Intelligent Transportation System

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5400: Design Intelligent Transportation System (ITS)

Description. ITS projects should be designed in accordance with the National ITS Architecture. ITS applications include the following:

  • Integration of traffic control and transportation management systems
  • Traffic signals which adapt to traffic and change their timing in each cycle
  • Highway advisory radio (HAR) systems
  • Vehicle detection
  • Closed-Circuit Television (CCTV)
  • Lane Control Signals (LCS)
  • Communication infrastructure.

The project manager should coordinate work with the district traffic engineer, the Traffic Operations Division, and the Technology Services Division (TSD) to ensure compliance with IT core architecture and other TxDOT requirements.

Pertinent Project Types. Projects involving high traffic volumes or complex traffic movements. However, rural projects with lower traffic volumes may call for ITS applications.

Responsible Party. Project manager, traffic operations engineer

Sub-tasks.

  • Find out where traffic barrier will be located, and try to place hazardous objects behind barriers that are already proposed for other purposes.
  • Obtain recent information on ITS alternatives, this is a rapidly advancing field.
  • Incorporate standard communications equipment when possible
  • Consult with the District Traffic Engineer and the Traffic Management Section of the Traffic Operations Division.
  • When possible, submit plans to Traffic Operations Division for early review.

Helpful Suggestions.

  • It is important to involve the Traffic Management Section of the Traffic Operations Division as early as possible in a project with ITS elements. Technical assistance is available for designing ITS and for developing contracts for ITS design or construction.
  • Consider future maintenance requirements for the system. Design to minimize maintenance but also consider how maintenance will be performed safely with minimum impact on traffic.
  • Utilize existing structures and roadside barriers for ITS, when possible.

Critical Sequencing. ITS plans should be designed concurrently with roadway plans to assure that necessary provisions, such as mounting structures and conduit systems, are made part of the overall plans.

Resource Material.

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Signals

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5420: Design signalization plan

Description. A comprehensive investigation of traffic conditions and characteristics of potential signal locations is necessary to determine the need for signal installations and to collect data for the design and operation of signals. Traffic control signals should not be installed unless the investigation reveals that at least one of the warrants contained in the Texas Manual on Uniform Traffic Control Devices ( TMUTCD) is met. Meeting a volume warrant is only the first step to justifying a traffic signal. The TMUTCD states that engineering judgment is required and that all factors should be considered when determining if a traffic signal should be installed.

Signal operation types include full-actuated, semi-actuated, pre-timed, or combinations thereof. They can also be operated at isolated intersections, in coordination with nearby signals, or as mid-block operations.

Pertinent Project Types. Projects warranting signalization.

Responsible Party. Traffic engineer

Sub-tasks.

  • Obtain or perform a signal warrant study.
  • A roadway design engineer may design the signals and prepare the plans; however, a traffic or transportation engineer should carefully check the design and specifications.
  • Coordinate plans with the roadway design engineer, drainage engineer, etc.
  • Coordinate signal design and details with local government if signals will be operated and maintained by a local government.
  • Obtain concurrence from the local government for locating signals within their jurisdiction and ensure that required agreements are executed as described in the TxDOT Contract Management Manual, Traffic Engineering Agreements, Chapter 15.
  • Obtain preliminary roadway, drainage, and utility adjustment plans.
  • Obtain existing and design year traffic data.
  • Make a site visit to inspect existing conditions and to verify minimum visibility distances.
  • Order and obtain geotechnical foundation designs for signal foundations.
  • Develop traffic signal layouts (see the PS&E Preparation Manual, Chapter 2, Section 2, Traffic Signal Layout).

Helpful Suggestions.

  • Technical assistance is available from the district traffic engineer and the Traffic Engineering Section of the Traffic Operations Division.
  • Coordinate intersection geometry, turn lane lengths, median types, and access control at signalized intersections. In urban areas having remote signal timing control and coordinated signals, signal control design should be discussed with the local entity.
  • Signal supports should be located to maximize safety and meet ADAAG and TAS requirements regarding accessibility requirements. All pedestrian features, including pushbuttons to activate pedestrian signals, must be accessible to persons with disabilities.
  • Detail intersection striping before preparing signal layouts to ensure proper location of signal heads.
  • Pedestrian crossing times should be sufficient for the expected user population to cross the street safely, and meet or exceed the requirements contained in the TMUTCD.

Resource Material.

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Signing and Striping

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5440: Design signing and pavement markings

Description. Signing and pavement marking plans include plan view layouts of final signs, striping, pavement markers, and other pavement markings. Show cross sections and sign size and legend details for the locations of all overhead signs. Detail all ground mounted guide signs and reference locations on the plans. Use sign summary sheets to detail color, location, size of structural steel.

Pertinent Project Types. All projects.

Responsible Party. Traffic engineer

Sub-tasks.

  • Obtain roadway and drainage plans.
  • Prepare a signing, striping, and pavement marking schematic and obtain preliminary approval from the Traffic Operations Division for roadways with new guide signing. This is not required for upgrades of existing signs; in this case, plans can be prepared without schematics.
  • Obtain a geotechnical survey and coordinate with a structural engineer when designing overhead sign bridge foundations.
  • Coordinate plans with the roadway design engineer.
  • Prepare final signing and pavement marking plans.

Helpful Suggestions.

  • Roadway and traffic engineers should coordinate intersection and ramp geometry early in the design process. There may be some areas of channelization improvement that become apparent only when preliminary striping designs are prepared.
  • Roadway and traffic engineers need to coordinate lane transitions at project ends (especially lane drops) during early stages of design. The combination of signing and design speed requirements will likely require the lane transition to be longer than geometrically necessary.
  • Overhead sign bridge supports should be located to maximize safety.
  • Striping of pedestrian facilities, such as crosswalks, must be closely coordinated with the design of curb ramps.

Critical Sequencing. Preliminary design can be as simple as a line diagram showing proposed number of lanes, lane drops, and proposed overhead and large ground mounted, guide signs and their proposed locations.

Resource Material.

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