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14th Amendment Highway Study - Task 7a: Design Levels

Prepared for
Federal Highway Administration

Prepared by
Cambridge Systematics, Inc.
and
PBS&J, an Atkins Company
October 28, 2010

Introduction

This preliminary technical memorandum is being submitted in partial fulfillment of Task 7 of the 14th Amendment Highway Corridor Study. It presents recommendations for design levels that would be utilized in the proposed alternative alignments. The next Expert Working Group (EWG) meeting is scheduled for December 2010, and the recommendations presented in this memorandum, along with proposed alignments, will be presented to the EWG for input at that time.

Design Levels

SAFETEA-LU specifies that the contractor will identify four alignments/design levels for the 14th Amendment Highway. An alternative may include an alignment with a design level that changes (i.e., is a freeway for a portion and an Interstate for another portion). Among these design levels, at least one must be to full Interstate standards. Furthermore, at least one design level shall use substantial portions of existing highways. The four proposed design levels are discussed below. It is important to note that the standards discussed below apply to both rural and urban areas. In urban areas, design variances may be necessary where required by cost, right-of-way, engineering constraints, environmental constraints, and/or public input.

1. Interstate Standard Design Level

This design level would incorporate existing Interstates 55, 59, 20, 85, 75 and 16, the proposed I-85 Extension, and various U.S. and state routes in order to create the 14th Amendment Highway. The I-85 Extension is proposed to be constructed as an Interstate facility. Other existing U.S. primary and state routes would require substantial improvements in order to meet Interstate standards. The minimum standard for this design level would be an urban Interstate facility. In Mississippi, the typical minimum standard (see Figure 1) would be two or three 12-foot travel lanes (in each direction) with a minimum 40-foot median, 8-foot inside shoulders and 10-foot outside shoulders. In Alabama, the typical minimum standard (see Figures 3 and 4) would be two to three 12-foot travel lanes (in each direction) with a concrete barrier median, 12-foot inside shoulders and 14-foot outside shoulders. In Georgia, the minimum standard (see Figures 6 and 8) would be two or three 12-foot travel lanes (in each direction) with a concrete barrier median, 14-foot, 10-inch insider shoulders and 14-foot outside shoulders.

2. Expressway Standard Design Level

This design level is a divided roadway that would utilize existing Interstates and U.S. and state routes. Full access control would occur along the existing Interstates. Along the U.S. and state routes, this design level would utilize grade separated intersections and would consolidate driveways as much as possible. The minimum design standard for this design level would be a four lane divided roadway with grade separated intersections and a variable width median.

3. Highway Standard Design Level

This design level is a divided roadway with at least some access control and would utilize existing Interstates and U.S and state routes. Full access control would occur along the existing Interstates. The intersections along the U.S. and state routes would be grade separated where practicable (based on projected traffic volumes, cost, right-of-way, engineering constraints, environmental constraints, and/or public input), and existing driveways would be consolidated as much as possible. The minimum design standard for this design level would be a four lane divided roadway with at-grade intersections and a variable width median.

4. Arterial Standard Design Level

This design level is a divided roadway with no access control. It would utilize existing U.S. and state routes, some of which would require improvements to meet the minimum acceptable design standard. The minimum design standard for this design level would be a four lane divided roadway with at-grade intersections and a variable width median.

Typical Sections

Typical sections for Interstate (both four and six lane facilities) as well as four lane divided facilities are included on the following pages. These typical sections were obtained from the Departments of Transportation of Georgia, Alabama and Mississippi, and will be revised as needed as more detailed alternative discussions continue.

It should be noted that in urban areas, design variances may be required to avoid impacts to sensitive environmental features or community resources. Through context sensitive design, a minimal acceptable typical section would be developed for these areas. For example, typical urban design levels could include a four lane undivided section or a five lane section (two travel lanes in each direction with a 14-foot flush median or two-way left turn lane).

Mississippifig1

 

Figure 1: Six Lane Divided Urban Interstate Typical Section

Fig 2

Figure 2: Four Lane Divided Rural Typical Section
(Interstate, Expressway, Arterial and Highway)

Alabama

Fig 3

Figure 3: Six Lane Divided Interstate Typical Section

Fig 4

Figure 4: Four Lane Divided Interstate Typical Section

Fig 5

Figure 5: Four Lane Divided Typical Section

Georgia

Fig 6

Figure 6: Six Lane Divided Urban Interstate Typical Section

Fig 7

Figure 7: Six Lane Divided Rural Interstate Typical Section

Fig 8 

Figure 8: Four Lane Divided Urban Interstate Typical Section

Fig 9

Figure 9: Four Lane Divided Rural Interstate Typical Section

Fig 10

Figure 10: Four Lane Divided Urban Section

Fig 11

Figure 11: Four Lane Divided Rural Section

Updated: 03/22/2013
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