9.2.9 Superelevation

Table 9-5
and
Table 9-6
show minimum superelevation rates of various radii and design speeds for an e
max
 of 6 percent and 8 percent, respectively. For multi-lane facilities, particularly where wide medians are used,
the radius applies to the innermost travel lane.
Table 9-5: Minimum Radii and Superelevation Rates
1
 for Mobility Corridors, e
max
 = 6%
Superelevation
Rate,
e
(%)
85
mph
R (ft)
90
mph
R (ft)
95
mph
R (ft)
100
mph
R (ft)
NC
2,3
30,104
38,571
50,139
66,667
RC
4,5
14,290
15,850
18,350
22,010
2.2
12,930
14,360
16,650
19,970
2.4
11,790
13,120
15,230
18,270
2.6
10,830
12,070
14,020
16,830
2.8
10,000
11,170
12,990
15,600
3.0
9,290
10,400
12,100
14,530
3.2
8,660
9,710
11,320
13,590
3.4
8,110
9,110
10,630
12,770
3.6
7,610
8,580
10,010
12,040
3.8
7,170
8,100
9,460
11,380
4.0
6,770
7,660
8,970
10,790
4.2
6,410
7,270
8,520
10,250
4.4
6,080
6,920
8,110
9,770
4.6
5,780
6,590
7,740
9,330
4.8
5,510
6,300
7,400
8,920
5.0
5,260
6,020
7,090
8,540
5.2
5,020
5,770
6,800
8,200
5.4
4,790
5,530
6,530
7,880
5.6
4,550
5,310
6,280
7,580
5.8
4,260
5,040
6,020
7,280
6.0
3,710
4,500
5,470
6,670
Notes:
  1. Computed using Superelevation Distribution Method 5. Refer to AASHTO’s A Policy on Geometric Design of Highways and Streets for the different types of Superelevation Distribution Methods.
  2. a) The term “NC” (normal crown) represents an equal downward cross-slope, typically 2%, on each side of the axis of rotation.
    b) The minimum curve radii for normal crown are suitable up to 3.0%.
    c) 3.0% normal crown should only be used when 3 or more lanes are sloped in the same direction.
    d) 1.5% or flatter normal crown should only be used for the design of special circumstance, such as table-topping intersections, or the evaluation of existing conditions.
  3. The minimum radii for normal crown (NC) are computed assuming a cross slope of-2.0% with side friction limited to 0.036, 0.034, 0.032, and 0.030 for 85, 90, 95 and 100 mph respectively. If outer lanes are sloped at -3.0% it is assumed traffic will be at the lower running speeds.
  4. The term “RC” (reverse crown) represents a curve where the downward, or adverse, cross-slope should be removed by superelevating the entire roadway at the normal cross-slope rate.
  5. For curve radii falling between normal crown and reverse crown, a plane slope across the entire pavement equal to the normal crown should typically be used. A transition from the normal crown to a straight-line cross slope will be needed.
Table 9-6: Minimum Radii and Superelevation Rates¹ for mobility Corridors e
max
= 8%
Superelevation Rate, e (%)
85 mph R (ft)
90 mph R (ft)
95 mph R (ft)
100 mph R (ft)
NC
2,3
30,104
38,571
50,139
66,667
RC
4,5
14,700
16,220
18,730
22,400
2.2%
13,330
14,740
17,020
20,360
2.4%
12,200
13,500
15,600
18,660
2.6%
11,240
12,450
14,400
17,220
2.8%
10,420
11,550
13,370
15,990
3.0%
9,700
10,780
12,470
14,920
3.2%
9,080
10,100
11,690
13,990
3.4%
8,530
9,490
11,000
13,160
3.6%
8,040
8,960
10,390
12,430
3.8%
7,600
8,480
9,840
11,770
4.0%
7,210
8,050
9,350
11,180
4.2%
6,850
7,660
8,900
10,650
4.4%
6,530
7,310
8,490
10,160
4.6%
6,230
6,990
8,120
9,720
4.8%
5,960
6,690
7,780
9,320
5.0%
5,710
6,420
7,470
8,940
5.2%
5,480
6,170
7,180
8,600
5.4%
5,260
5,930
6,910
8,280
5.6%
5,060
5,720
6,670
7,980
5.8%
4,880
5,520
6,440
7,700
6.0%
4,710
5,330
6,220
7,450
6.2%
4,550
5,150
6,020
7,210
6.4%
4,390
4,990
5,830
6,980
6.6%
4,250
4,830
5,650
6,770
6.8%
4,120
4,690
5,490
6,570
7.0%
3,990
4,550
5,330
6,380
7.2%
3,870
4,420
5,180
6,200
7.4%
3,760
4,300
5,040
6,030
7.6%
3,640
4,180
4,900
5,870
7.8%
3,510
4,070
4,780
5,720
8.0%
3,210
3,860
4,630
5,560
  1. Computed using Superelevation Distribution Method 5. Refer to AASHTO’s A Policy on Geometric Design of Highways and Streets for the different types of Superelevation Distribution Methods.
  2. a) The term “NC” (normal crown) represents an equal downward cross-slope, typically 2%, on each side of the axis of rotation.
    b) The minimum curve radii for normal crown are suitable up to 3.0%.
    c) 3.0% normal crown should only be used when 3 or more lanes are sloped in the same direction
    d) 1.5% or flatter normal crown should only be used for the design of special circumstance, such as table-topping intersections, or the evaluation of existing conditions.
  3. The minimum radii for normal crown (NC) are computed assuming a cross slope of-2.0% with side limited to 0.036, 0.034, 0.032, and 0.030 for 85, 90, 95 and 100 mph respectively. If outer lanes are sloped at -3.0% it is assumed traffic will be at the lower running speeds.
  4. The term “RC” (reverse crown) represents a curve where the downward, or adverse, cross-slope should be removed by superelevating the entire roadway at the normal cross-slope rate.
  5. For curve radii falling between normal crown and reverse crown, a plane slope across the entire pavement equal to the normal crown should typically be used. A transition from the normal crown to a straight-line cross slope will be needed.