10.6.2 Basic Design Criteria

Recommended design values are shown in
Table 10-2
.
Table 10-2 Design Criteria for Super 2 Highway
Minimum
Preferable
Design Speed (mph)
See applicable rural two- lane criteria in App. A
See applicable rural multi lane criteria in App. A
Clear Zone (ft)
See applicable rural two- lane criteria in App. B
See applicable rural multi lane criteria in App. B
Lane Width (ft)
11
12
Shoulder Width (ft)
3
1,3
8 - 10
Passing Lane Length (mi)
1
1.5 - 2
2
Notes:
  1. Where ROW is limited.
  2. Longer passing lanes are acceptable, but more than 4 miles is not recommended. Consider switching the direction if more than 4-mi.
  3. A 5-ft minimum clear space for bicyclists should be provided on bridges being replaced or rehabilitated (An SUP may be used in lieu of the bicycle clear space). Off-system Bridges, with current ADT greater than 400 ADT, where this addition may represent an unreasonable increase in cost may be excepted from the bicycle clear space requirement. See Chapter 12 for specific off-system bridge requirements for current ADT of 400 or less.
The length for opening a passing lane (
Figure 10-2
) should be based on the following:
L=ws2
The taper length for closing a passing lane (
Figure 10-2
) should be based on:
L = WS
Where:
L = Length of taper (ft),
W = Lane width (ft), and
S = Posted speed (mph).
Opening and Closing an Outside Passing Lane ( click in image to see full-size image)
Figure 10-2: Opening and Closing an Outside Passing Lane
When switching the passing lane from one direction to another (closing the inside 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) preferable) between them (
Figure 10-3
).
Closing an Inside Passing Lane ( click in image to see full-size image)
Figure 10-3: Closing an Inside Passing Lane
When opening an inside passing lane in each direction (
Figure 10-4
), provide a taper length based on L= WS/2.
Opening an Inside Passing Lane ( click in image to see full-size image)
Figure 10-4: Opening an Inside Passing Lane
When widening to the outside of the roadway to provide a passing lane opportunity (
Figure 10-5
), 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)
Figure 10-5: Separated Passing Lanes with an Outside Widening
Passing lanes in each direction may overlap if ROW is sufficient (
Figure 10-6
).
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)
Figure 10-6: Side by Side Passing Lanes