9.4.4 Acceleration and Deceleration Lengths

Table 9-13
provides design criteria for exit ramp deceleration lengths. Grade adjustment factors for deceleration lanes are shown in
Table 9-15
.
Table 9-13: Minimum Deceleration Lane Lengths for Exit Ramp Speed Change Lanes with Flat Grades of Less than 3 Percent
Design Speed of Controlling Feature on Ramp, V’ (mph)
55
60
65
70
75
80
85
90
Highway Design Speed, V (mph)
Deceleration Lane Length
1
, La (ft)
85
445
385
330
275
220
125
-
-
90
495
445
395
350
305
235
135
-
95
535
490
445
410
380
315
240
135
100
575
535
495
465
445
395
330
250
Notes:
  1. Where providing desirable deceleration length is impractical, it is acceptable to allow for a moderate amount of deceleration (10 mph) within the through lanes prior to the beginning of the exit ramp.
Table 9-14
provides design criteria for entrance ramp acceleration. Speed change lane adjustment factors for grade effects are shown in
Table 9-15
. A minimum taper length of 600-ft is suitable for parallel type acceleration lanes for design speeds up to 100-mph. For tapered acceleration lanes, a minimum taper length of design speed (DS) to 1 must be used.
Table 9-14: Lengths of Entrance Ramp Speed Change Lanes
Design Speed of Controlling Feature on Ramp, V’ (mph)
55
60
65
70
75
80
85
90
Highway Design Speed, V (mph)
Acceleration Lane Length, La (ft)
85
875
620
375
110
-
-
-
-
90
1095
850
595
355
-
-
-
-
95
1340
1110
850
635
270
-
-
-
100
1620
1405
1135
960
580
140
-
-
Table 9-15: Speed Change Lane Adjustment Factors as a Function of a Grade
Deceleration Lanes
Design Speed of Roadway (mph)
Ratio of Length on Grade to Length on Level
1
3 to 4% Upgrade
3 to 4% Downgrade
5 to 6% Upgrade
5 to 6% Downgrade
All
0.9
1.2
0.8
1.35
Acceleration Lanes
Design Speed of Roadway (mph)
Ratio of Length on Grade to Length on Level for Design Speed (mph) of Turning Roadway Curve
1
20
25
30
35
40
45
50
All Speeds
3 to 4% Upgrade
3 to 4% Downgrade
85
1.62
1.69
1.75
1.80
1.89
1.99
2.10
0.56
90
1.66
1.73
1.80
1.86
1.96
2.08
2.20
0.55
95
1.71
1.78
1.85
1.92
2.03
2.17
2.30
0.54
100
1.75
1.83
1.90
1.98
2.10
2.26
2.40
0.52
5 to 6% Upgrade
5 to 6% Downgrade
85
2.39
2.51
2.64
2.94
3.15
3.73
4.28
0.46
90
2.50
2.64
2.77
3.10
3.33
4.00
4.65
0.45
95
2.62
2.76
2.91
3.27
3.51
4.26
5.03
0.44
100
2.74
2.89
3.04
3.43
3.69
4.53
5.40
0.42
Notes:
  1. Ratio in this table multiplied by length of deceleration or acceleration distance in Table 9-13 and Table 9-14.