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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 slower vehicles to pass and traffic platoons to disperse. 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, prevalence of head-on crashes, 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 availability and ease of construction.

Some issues to consider when designing a Super 2 project:

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  • Analyze existing right-of-way width considerations to determine feasibility of upgrading to a Super 2;
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  • Consider providing a left turn or right turn lane if a significant traffic generator falls within the limits of a Super 2;
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  • Consider providing wider shoulders (8-ft to 10-ft) in areas with high driveway density;
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  • Evaluate the location and associated treatment to achieve clear zone values at large drainage structures and bridges when considering the placement of passing lanes;
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  • 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;
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  • Avoid terminating 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;
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  • Consider traffic operations, unexpected lane changes, and intersection geometrics when evaluating the termination of a passing lane at an intersection. If termination of the passing lane at the intersection would result in significant operational lane weaving, then consider extending the passing lane beyond the intersection;
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  • Provide adequate sight distance (stopping sight distance desirable) between the end of a lane termination taper and a constraint such as metal beam guard fence, a narrow structure, or major traffic generator; and
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  • 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 for Super 2 Highway

Minimum

Desirable

Design Speed (mph)

See Table 4-2

See Table 4-1

Clear Zone (ft)

See Table 4-2

See Table 4-1

Lane Width (ft)

11

12

Shoulder Width (ft)

31

8 - 10

Passing Lane Length (mi)

1

1.5 - 22

Notes:

  1. Where ROW is limited.
  2. Longer passing lanes are acceptable, but more than 4-mi are not recommended. Consider switching the direction if more than 4-mi.


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

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

Where

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

Figure 4-1. Opening and Closing an Outside 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 an Inside Passing Lane (click in image to see full-size image) Anchor: #XDYITJOCgrtop

Figure 4-2. Closing an Inside Passing Lane

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

Opening an Inside Passing Lane (click in image to see full-size image) Anchor: #UKSSXMODgrtop

Figure 4-3. Opening an Inside Passing Lane

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 an Outside Widening (click in image to see full-size image) Anchor: #XAISFVXGgrtop

Figure 4-4. Separated Passing Lanes with an Outside Widening

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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