7.9 Operational Design

Operational design involves design of signals, illumination, signs, pavement markings and intelligent transportation systems (ITS). Construction plans result from each of the tasks within this section.

7.9.1 Signals

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 must not be installed unless the investigation reveals that at least one of the warrants contained in the TMUTCD is met. Meeting an hourly volume warrant is only the first step to justifying a traffic signal. The TMUTCD states that warrants are a threshold condition and not a substitute for engineering judgment. All traffic factors must be considered when determining if a signal(s) must 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.
If the department is not responsible for the traffic control signal system operation and maintenance (e.g., appurtenances, software, hardware and timing), then an agreement must be established with the controlling agency before the signal is installed and activated.
Considerations in the design of traffic signals include:
  • Coordinate signal design and details with LG if signals will be operated and maintained by a LG. Obtain concurrence from the LG for locating signals within their jurisdiction and ensure that required agreements are executed as described in TxDOT’s
    Negotiated Contracts Procedures Manual
    ;
  • Coordinate signal plans with roadway, drainage and utility plans;
  • Coordinate to have geotechnical foundation design performed for traffic signal foundations with District bridge and laboratory staff;
  • Coordinate intersection geometry, turn lane lengths, median types, and access control at signalized intersections with roadway and traffic engineers. In urban areas having remote signal timing control and coordinated signals, signal control design must be discussed with the local entity. If the project is located along a designated bike route, bicycle signals may be appropriate, and should be linked and timed with the vehicular traffic signals. Any through bicycle movements will require prohibiting permissive movements for vehicles (e.g., not right on red), see the TMUTCD for further guidance.
  • Signals and supports must be located to maximize safety and meet PROWAG and TAS accessibility requirements. All pedestrian features and pedestrian signal poles must be accessible to persons with disabilities;
  • Detail intersection pavement markings, ramps, and walkways before preparing pedestrian signal layouts to ensure proper location of pedestrian poles and signal heads;
  • Account for mid-block pedestrian signals as necessary; and
  • Pedestrian crossing times must be sufficient for the expected user population to cross the street safely and meet or exceed the requirements contained in the TMUTCD.

7.9.2 Illumination

There are two types of roadway lighting: continuous lighting and safety lighting.
Safety lighting is typically needed at interchanges, decision points, high-volume rural or suburban intersections, weigh stations, rest areas, and for safety/security for pedestrians, bicyclists and transit users.
Continuous lighting provides uniform lighting on all mainlanes, ramp terminals, direct connectors and interchanges. Continuous lighting requires the financial participation of the city. Either type may use conventional roadway lighting or high mast poles.
An FAA form 7460-1 must be completed according to 14 CFR §77.9 when lighting exceeds the following conditions for public use airports, military airport, airport operated by a Federal agency or DOD, and airport or heliport with at least one FAA-approved instrument approach procedure. If lighting does not exceed the following conditions, then the form does not need to be filed. Required notification applies to any construction, alteration, or installation of illumination support:
  • Exceeding 200 feet above ground level (AGL);
  • Within 20,000 feet of any airport type listed above which exceeds 100:1 surface from any point on the runway of each airport, with its longest runaway is more than 3,200 feet;
  • Within 10,000 feet of any airport type listed above which exceeds 50:1 surface from any point on the runway of each airport, with its longest runway no more than 3,200 feet; and
  • Within 5,000 feet of any heliport listed above which exceeds a 25:1 surface.
Considerations in the design of illumination include:
  • Coordinate illumination plans with roadway, drainage, traffic and utility plans;
  • Coordinate with LG for maintenance of proposed continuous lighting;
  • Design high mast foundations according to bore logs and HMIF standards;
  • Determine illuminance design values according to roadway classification and AASHTO’s Roadway Lighting Design Guide;
  • Execute the appropriate continuous or safety lighting agreement with the LG when lighting is to be installed within a LG's jurisdiction;
  • For lighting on bridges, coordinate illumination design with bridge details so conduit and bridge lighting brackets are included in the bridge plans; this will avoid unsightly conduit additions to bridges;
  • Meet Texas statute Health and Safety Code Chapter 425 by using cutoff luminaires to minimize glare and light pollution when installing lighting using state funds;
  • Prepare lighting justification report;
  • Use breakaway devices according to TxDOT’s
    Highway Illumination Manual
    and AASHTO requirements;
  • When designing lighting for a walkway/bikeway adjacent to a roadway, the roadway must be lit to the same level as the walkway; and
  • When possible, place lighting outside clear zone. If lighting must be in the clear zone, use breakaway poles or place poles behind or on a traffic barrier.

7.9.3 Signing and Pavement Markings

Signing and pavement marking plans include plan view layouts of final sign and pavement marking types and locations, account for applicable on-street bikeway pavement markings and bike route signs. Include cross section, sign size and legend details for the locations of all overhead signs. Detail all ground mounted large guide signs and reference locations on the plans. Use sign summary sheets to detail support type, color, number of posts, and size of structural steel.

7.9.4 Intelligent Transportation System (ITS)

ITS projects must be designed in accordance with the National ITS Architecture. The ITS system aims to solve congestion and safety problems and improve operating efficiency in freight and transit movement.
ITS applications include the following:
  • Closed-Circuit Television (CCTV) to monitor traffic conditions and incidents
  • Communication infrastructure;
  • Dynamic Message Signs (DMS);
  • Integration of traffic control and transportation management systems;
  • Lane Control Signals (LCS) to warn the public of lane closures due to incidents or construction;
  • Traffic detection devices;
  • Traffic maps - congestion, construction, weather;
  • Traffic signals which adapt to traffic and change their timing in each cycle; and
  • Travel time estimation.
ITS work must be coordinated with the District traffic staff, TRF – Traffic Management Section and the Information Management Division (IMD) to ensure compliance with IT core architecture and other TxDOT requirements.
The department maintains a statewide radio network providing signal and radio technical support and coordinating radio frequency licenses. The Highway Advisory Radio Stations (HARS) are low power AM stations that broadcast highway related information to the traveling public. FCC regulations require that traveler information stations transmit only noncommercial voice information pertaining to traffic and road conditions.
By Executive Order, June 14, 2012, federal-aid highways and ROW can be used to deploy both wired and wireless broadband infrastructure creating funding opportunities for state and local transportation infrastructure to help expand broadband infrastructure. Broadband access also affords public safety agencies better interoperability and effectiveness.
Considerations in the design of ITS include:
  • Find out where traffic barrier will be located and try to place hazardous objects behind barriers that are already proposed for other purposes;
  • Obtain current information on ITS alternatives, this is a rapidly advancing field;
  • Incorporate standard communications equipment when possible;
  • Consult with the District traffic staff and TRF – Traffic Management Section;
  • When possible, submit plans to TRF for early review;
  • 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;
  • Consider placement of DMS in areas where there is not a high probability of a simultaneous workload required for drivers (i.e., high-decision locations, high-speed merging, and weaving);
  • Consider ITS regional opportunities and possible connections to manage traffic through long corridors; and
  • Utilize existing structures and roadside barriers for ITS, if possible.
  • Coordination:
  •  District roadway, bridge, traffic and utility staff
  •  DES staff
  •  TRF staff
  • Available training:
  •  TCC322 – Signal Operations and Maintenance
  •  TCC348 – Fundamental of Traffic operations
  •  TRF302 – Signal Tech Training – Basic
  •  TRF450 – TxDOT Roadway Illuminations and Electrical Installations
  •  TRF504 – Principles of Freeway Guide Signing