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Table of Contents | Appendix A Table of Contents

Rural Interstate Corridor Communications Study
Report to States
Appendix A

2.0 Preliminary Backbone Alignments

As part of the task to develop the Report to States, a preliminary backbone alignment plan for telecommunications has been developed and presented in electronic format. The purpose of the preliminary backbone alignment is to serve as a high-level design guide for a State agency or private telecommunications partner that will allow them to estimate the level of effort required to install the telecommunications infrastructure. The backbone infrastructure included in this study includes wireline, when conduit is buried and filled with fiber optic cable, and wireless infrastructure in the form of tower locations.

The products of the Rural Interstate Corridor Communications Study are informational only. This study does not obligate Federal, State, or local governments to implement any of the study findings. The products of the study are intended only to inform public and elected officials.

2.1 Backbone Alignment Development Process

The traditional method of delivering plans would consist of hard copies of plan sheets. The study team for this project determined that electronic files utilizing Google Earth as a base map would provide the most flexibility for storing, displaying, and using the preliminary backbone alignment files. The electronic Google Earth KML (KML, or Keyhole Markup Language, is an XML grammar and file format for modeling and storing geographic features such as points, lines, images, polygons, and models for display in Google Earth and Google Maps. KML can be used to share places and information with other users of Google Earth and Google Maps) files have been enhanced with the addition of lineation, symbols, and icons representing various existing and proposed infrastructure elements. The details included in the alignment files, criteria for placement, and the icons used are defined below. The electronic files can be obtained from the FHWA.

2.1.1 Alignment Details Shown

The following list contains topography elements, site-condition, and communication infrastructure details that are included in the preliminary backbone alignment files:

  • Proposed conduit routing;
  • Proposed boring locations;
  • Proposed bridge attachment locations;
  • Proposed access points (including handholes/ vaults);
  • Proposed regeneration stations;
  • Existing tower locations;
  • Proposed tower locations;
  • State DOT district offices and facilities;
  • Major Streams and Rivers;
  • State Borders;
  • Existing Weigh Stations;
  • Existing Rest Areas; and
  • Existing potential environmentally sensitive area.

2.1.2 Study Team Visual Field Surveys

In order for the study team to be able to enhance the design content of the preliminary backbone alignment plans, field visits along the I-90 and I-20 Corridors were undertaken to record details and make location decisions that would not have been possible solely through the use of aerial photography, as provided by Google Earth. In the fall of 2007, study teams performed visual surveys by driving the two Corridors and recording their findings in electronic Google Earth base files. During these visual surveys, the teams recorded the preferred alignments for conduit placement, handhole locations, locations where directional boring would be required, potential locations for future wireless towers on State right-of-way (ROW), and bridge and overpass information.

2.2 Preliminary Backbone Alignment Design Criteria

2.2.1 General Criteria

To the best extent possible, preliminary designs for all utility infrastructure installed on State-owned access-controlled ROW are consistent with the State's Utility Accommodation Policy (UAP) and the laws and requirements of the State. Before final designs are completed, the policies and regulations of each State should be consulted and adhered to in the final design plans. Private partners involved in the installation of telecommunications infrastructure on State ROW also may have criteria to be considered in the final designs of such infrastructure.

2.2.2 Fiber Optic Line Placement

The design assumes that conduit for fiber optic cable will be installed by plowing or trenching methods with directional boring to navigate under roadways, streams, or other obstacles. Decisions about the side of the right-of-way in which the conduit is to be placed are based on several factors, including width of ROW, potential obstacles, presence of rock or environmentally sensitive areas, and access for heavy equipment and maintenance personnel. The location and depth of the conduit should follow the State's UAP and is generally near the ROW line and/or a safe distance away from existing utilities to avoid the possibility of disruption. Directional boring locations are shown where the conduit passes under a roadway or railroad, at stream crossings where bridge attachments are not necessary or allowed, where conduit may cross the Interstate highway, and to avoid obstacles in the ROW such as ditch lining.

2.2.3 Handhole/Vault Locations

Handholes/vaults are used to access the conduit and fiber optic cable for making splice connections or for the installation of fiber optic cable into the conduit. In this document, the terms handholes and vaults are considered interchangeable and represent a box to accommodate all aspects of fiber optic cable installation such as pulling points, coiling, splicing, etc. For this design handholes have been placed at interchanges, tower locations, weigh stations, and rest areas. For the purposes of pulling fiber into the conduit, handholes are generally located at one-mile intervals (minimum) where the above criteria cannot be met.

Figure 2.1: Handhole Icon

Figure 2-1 - graphic - Icon of handhole location.

As a future consideration, the latest recommendations from the Vehicle Infrastructure Integration (VII) consortium for future installation of Roadside Equipment (RSE) locations is that drivers should pass an RSE at a minimum of once every 10 minutes. Assuming an average speed of 65 mph, and that every RSE requires one handhole, this would necessitate a handhole every 10.8 miles. The recommended design criteria exceed the minimum criteria noted above for the future VII.

2.2.4 Regeneration Building Placement

Regeneration stations or POP (Point of Presence) sites are locations where the signal being transmitted through fiber optic cable is regenerated and transmitted further along the fiber optic path. These POP facilities are also utilized as a location where connections to local networks are made. The criteria for placement of the regeneration buildings are based on the ability of existing fiber optic transmission equipment and cable to transmit a signal an average of 50 miles. Regeneration stations require access to electrical power, an important design consideration. Proposed regeneration buildings have been placed as closely as possible to 50-mile spacing where access is easily gained from a side road or other non-mainline access, such as an interchange or rest area. Regeneration building sites should have sufficient space to accommodate a 10’ x 20’ one-story building with room for parking one or two vehicles. A perimeter fence may be needed to secure the site (approximately a 1000 sq. ft. footprint). These facilities should be located outside of the clear zone.

Figure 2.2: Regeneration Station (POP) Icon

figure 2-2 - graphic - Icon of regeneration station location.

2.2.5 Directional Boring

Directional boring would be used at small stream crossings, where bridge attachments are not practical or not allowed by the State, at roads and railroads crossing under or over the Interstate highway, at interchanges, and at existing utilities (such as gas or oil pipelines). The preliminary design indicates directional bore locations with one icon representing the directional bore area versus two icons representing the entrance and exit bore pits. Where applicable, an icon representing a directional bore and handhole, such as at an interchange, has been used to minimize the number of icons at interchanges.

Figure 2.3: Directional Bore Icon

figure 2-3 - graphic - Icon of directional bore location.

2.2.6 Rock Cuts

When rock conditions exist, the use of a rock saw to create a trench will be required. Avoiding rock cuts is preferred and may require the conduit to be routed away from the ROW line and closer to the shoulder. Rock cuts will not be shown on the preliminary backbone alignments as geotechnical investigations should be done to determine where rock cuts are necessary.

2.2.7 Bridge Attachments vs. Stream Crossings

The criteria to determine bridge attachments versus directional boring under a river or stream will depend on State policy and approval. An application for a bridge attachment permit should be submitted when route design plans are submitted by the private entity or private partner prior to final design stage. For the purposes of the preliminary backbone alignment, bridges that span major rivers, railroad yards, or complicated interchanges are shown as bridge attachments (with permit approvals needed prior to final design). For bridge attachments, conduit should be encased in a bullet-proof shroud, located on the downstream side of the bridge, or protected by bridge beams to prevent damage from floating debris, and meeting all State standards for attachment of fixtures to bridges.

Figure 2.4: Bridge Attachment Icon

figure 2-4 - graphic - Icon of bridge attachment location.

2.2.8 Communication Tower Locations

Communication towers shown on the preliminary backbone alignments include existing public agency-owned communication towers and privately owned communication towers. This includes DOT-owned towers, other public agency towers, and towers indicated on the tower maps obtained by the project team. Potential tower locations to be considered for construction at a future date are indicated with an icon. The proposed tower locations allow for sufficient space for the towers and associated structures on public agency-owned ROW. The sites include a handhole and are potentially co-located with a regeneration building due to the availability of ROW associated with a tower site. If the States have identified locations where they are willing to allow a tower to be located, these are also shown.

Towers for use in the backbone become critical when construction of a fiber link is cost-prohibitive or physically difficult. Most tower locations shown on the preliminary backbone alignments are locations that would support middle or last mile connections, though some do represent where backbone links could be installed to reduce installation costs. Spacing of the towers for the backbone becomes dependent upon the transmitting and receiving equipment as well as the frequency used, so tower locations would have to be further designed to accommodate any backbone linkages that may be desired. Additional information on tower design is located in Section 3.0.

Figure 2.5: Potential Tower Location Icon

figure 2-5 - graphic - Icon of potential tower location.

2.3 Telecommunication Infrastructure Installation Details

For this study the preliminary backbone alignment plans have only been developed for two of the three Corridors identified in Section 5507 of SAFETEA-LU, Interstate 90 and Interstate 20. MassHighway and the Vermont Agency of Transportation along the Interstate 91 Corridor have independently progressed in the development of a Corridor communications program to the point where developing a preliminary backbone alignment defined by this study would have been of little value. Instead, the study team has developed a series of typical telecommunication installation details that can be used for future telecommunication construction projects. The typical installation details, listed below, are on plan sheets in Microstation and AutoCAD 2007 software format, and can be manipulated into a plan sheet based on the requirements of the agency preparing plans. Prints of all typical installation details developed, including electronic files, are under separate cover from this report and are available from the FHWA.

2.3.1 List of Typical Installation Details Developed

  • Junction Box Details (handhole/ vaults)
    • Installation Cross-Section
    • Cable Management Details
    • Various Sizes and Conduit Routing
    • Construction Notes
  • Cabinet Entrance Details
  • Under-Roadway Directional Boring Details
  • Conduit Trenching Details
    • Under Pavement
    • Open Ground
    • Adjacent to Roadways
  • Fiber Marker and Warning Tape Details
  • Conduit Routing at Interchanges
  • Conduit Bridge Attachment Details
  • Typical Regeneration Building

2.4 Use of the Preliminary Backbone Alignment Files

It should be noted that the preliminary backbone alignments developed as part of this study are, as the name suggests, preliminary and should not be considered a final design nor taken as any indication that a future project to install infrastructure of this type is imminent. The preliminary backbone alignments contained in these files are illustrative only and not an FHWA mandate on design of communication infrastructure. They are intended for information purposes such as preliminary estimation of quantities, identification of construction issues, and preliminary cost estimation to aid in discussions with potential private partners. If a State agency or private provider wishes to use the files to create more detailed designs, such use is allowed and encouraged.