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Section 6: Super 2 Highways

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Overview

A Super 2 highway is where a periodic passing lane is added to a two-lane rural highway to allow passing of slower vehicles and the dispersal of traffic platoons. The passing lane will alternate from one direction of travel to the other within a section of roadway allowing passing opportunities in both directions. A Super 2 project can be introduced on an existing two-lane roadway where there is a significant amount of slow moving traffic, limited sight distance for passing, and/or the existing traffic volume has exceeded the two-lane highway capacity, creating the need for vehicles to pass on a more frequent basis.

Widening of the existing pavement can be symmetric about the centerline or on one side of the roadway depending on right of way (ROW) availability and ease of construction.

Some issues to consider when designing a Super 2 project:

  • Existing ROW width considerations must be analyzed to determine feasibility of upgrading to a Super 2.
  • Consider providing a left turn lane if a significant traffic generator falls within the limits of a Super 2.
  • Consider providing full shoulders (8'-10') in areas with high driveway density.
  • The location of large drainage structures and bridges should be evaluated when considering the placement of passing lanes.
  • Evaluate traffic operations including truck volumes if consideration is given to terminating passing lanes on significant uphill grades. Coordinate passing lanes with climbing lane needs to improve operating characteristics.
  • Avoid closing a passing lane over a hill or around a horizontal curve where the pavement surface at the end of the taper isn't visible from the beginning of the taper.
  • When evaluating the termination of a passing lane at an intersection, consideration should be given to traffic operations turning and weaving movements, and intersection geometrics. If closure of the passing lane at the intersection would result in significant operational lane weaving, then consideration should be given to extending the passing lane beyond the intersection.
  • Allow adequate distance (recommend stopping site distance) between the end of a lane closure taper and a constraint such as metal beam guard fence, a narrow structure, or major traffic generator.
  • Consider providing the passing lane in the direction leaving an incorporated area for potential platoons generated in the urban area.
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Basic Design Criteria

Recommended design values are shown in Table 4-6.

Anchor: #i1012852Table 4-6: Design Criteria

Minimum

Desirable

Design Speed

See Table 4-2

Horizontal Clearance

See Table 4-2

Lane Width

11 ft

12 ft

Shoulder Width

3 fta

8 - 10 ft

Passing Lane Length

1 mi

1.5 - 2 mib

a. Where ROW is limited

b. Longer passing lanes are acceptable, but not recommended more than 4 miles. Consider switching the direction if more than 4 miles.



The length for opening a passing lane (Figure 4-1) should be based on the following:

L = WS/2,

Where

L = Length of taper,

W = Lane width, and

S = Posted speed.

The taper length for closing a passing lane (Figure 4-1) should be based on:

L = WS,

Where

L = Length of taper,

W = Lane width, and

S = Posted speed.

Opening and Closing a Passing Lane (click in image to see full-size image) Anchor: #JQKBAYTGgrtop

Figure 4-1. Opening and Closing a Passing Lane

When switching the passing lane from one direction to another (closing the passing lane in each direction), provide a taper length from each direction based on L = WS, with a minimum 50 ft buffer (stopping sight distance (SSD) desirable) between them. (Figure 4-2).

Closing the Passing Lane from One Direction
to Another (click in image to see full-size image) Anchor: #XDYITJOCgrtop

Figure 4-2. Closing the Passing Lane from One Direction to Another

When opening a passing lane in each direction (Figure 4-3), provide a taper length based on L= WS/2.

Opening the Passing Lane from One Direction
to Another (click in image to see full-size image) Anchor: #UKSSXMODgrtop

Figure 4-3. Opening the Passing Lane from One Direction to Another

When widening to the outside of the roadway to provide a passing lane opportunity (Figure 4-4), provide an opening taper length based on L = WS/2 and a closing taper length based on L=WS.

Separated Passing Lanes with Widening to
the Outside of Roadway (click in image to see full-size image) Anchor: #XAISFVXGgrtop

Figure 4-4. Separated Passing Lanes with Widening to the Outside of Roadway

Passing lanes in each direction may overlap if ROW is sufficient (Figure 4-5).

Provide an opening taper length based on L = WS/2 and a closing taper length based on L=WS.

Side by Side Passing Lanes (click in image to see full-size image) Anchor: #OXJHWWNRgrtop

Figure 4-5. Side by Side Passing Lanes

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