Section 6: Texas Highway Trunk System

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TxDOT Authority

Authorization for developing the Texas Highway Trunk System by TxDOT is found in the 43 TAC Chapter 15, Subchapter D.

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The suffering Texas economy of the mid-1980s led some areas of the state to request improvements to their highway network. Highway improvements were thought to result in increased travel and commerce in the region. Communities requested that particular highways within their regions be upgraded to four-lane divided highways. During this same time period, federal legislation was pending for the development of a NHS of interconnected principal arterial routes, which would serve major population areas, international border crossings, and other modal transportation facilities. The department decided to develop a long-range highway plan that would address the needs of local communities and incorporate required elements of the anticipated legislation. In the fall of 1988, the department began to develop the Texas Highway Trunk System (the Trunk System).

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The Trunk System is a network of rural divided highways that complements and includes elements of the Interstate Highway System. The minimal design criteria for this network specify that each highway should be at least a four-lane divided facility. The Trunk System will serve as a principal connector for all Texas cities with over 20,000 population as well as major ports and points of entry. The total mileage of the Trunk System, as stated in TxDOT Minute Order 910209, is limited to 11,500 miles. Copies of the Trunk System map may be obtained from TPP.

Originally a route had to meet one or more of the following criteria to be considered in or developed as part of the Texas Highway Trunk System:

  • maximize the use of existing four-lane divided roadways
  • minimize circuitous or indirect routing
  • connect with principal roadways from adjacent states
  • connect with principal deep-water ports with channel depths of 40 feet or more
  • connect with principal Mexican ports of entry
  • serve significant military or other national security installations
  • serve tourism and/or recreational areas
  • comprise major truck routes
  • be located within 25 miles or less of cities of 10,000 population or greater.
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Mobility Features

Critical to the Trunk System development is overall system mobility with a lesser emphasis on access. System features that contribute to mobility include grade-separation at points of intersection between Trunk System routes and other trunk routes, other intersecting roadways, and railroad crossings. Trunk System routes are given traffic-flow priority over other intersecting roadways. Traffic control strategies for other intersecting roadways include traffic signals and appropriate signs.

In developed or developing areas, access may be controlled by deed restriction or design, which may include provisions for frontage roads and grade separations. Control of access may be provided in the intersection areas or continuously, depending on traffic volumes, the degree or roadside development, or availability of right of way. Where access is not controlled by design or deed restriction, access driveways from adjacent property will be in accordance with TxDOT regulations for access to state highways.

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The Trunk System program identifies and prioritizes specific projects for right-of-way acquisition and construction authority. The expansion of Trunk System facilities is limited to those sections with two-lane cross sections. Criteria were developed to compare and rank facilities that are not currently four-lane divided roadways. Factors for prioritizing facilities for inclusion into the Trunk System include the following:

  • average daily traffic
  • truck traffic
  • user delay costs
  • construction
  • right-of-way and environmental mitigation costs
  • system continuity
  • role of international trade.
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Project Selection

Originally, projects were selected based on the Congestion Efficiency Index (CEI), but now most projects are selected based on “priority corridors.” TxDOT selects projects in the Trunk System Phase I Corridors on a statewide basis from candidate projects submitted by the districts. The department uses a Cost Efficiency Index to rank projects for selection. Major elements for the index are project cost and traffic volume. Additionally, TxDOT reserves 10 percent of the Trunk System funds to address projects not on the Phase I Corridors that require immediate attention due to safety, roadway condition, or other valid factors. Projects funded with this 10 percent will be selected using the ranking process.

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Design Criteria

The design features of Trunk System facilities adhere to guidelines set forth in TxDOT design manuals concerning facility type. The facility type may range from a completely access-controlled freeway to a partially access-controlled highway or a facility controlled only by TxDOT regulations regarding access to state highways.

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Relief Routes

When feasible, the Trunk System calls for the incorporation of access-control measures into existing relief-route facilities (Transportation Code, Section 203.003). Relief-route projects are prioritized for right-of-way acquisition and construction authority based on certain criteria. Similarly, facilities not developed to a minimum four-lane divided facility are compared and ranked based on the following criteria:

  • average traffic volume
  • truck traffic
  • user delay costs
  • construction
  • right of way
  • environmental mitigation costs.
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Rights of Way

Right of way should be initially purchased for the entire facility, although the facility will be developed in stages. The early acquisition of selected right of way, in certain instances, may be desirable along Trunk System routes. The priority of acquisition might not follow the approved project schedule in order to avoid delays and facilitate the economical considerations of acquisition.

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