9.4 Ramps and Direct Connectors

9.4.1 Overview

This section discusses ramps and direct connectors and includes information on the following topics:
  • Design speed;
  • Lane and shoulder widths;
  • Acceleration and deceleration lengths;
  • Distance between successive ramps;
  • Grades and profiles; and
  • Cross section and cross slopes.

9.4.2 Design Speed

Similar to facilities with design speeds of 80-mph or less, ramps on these facilities must have a relationship between the ramp design speed and the mainlane design speed. All ramps and direct connectors must be designed to enable vehicles to leave and enter the travel way of the highway at 85 percent (desirable) to 70 percent (usual minimum) of the highway design speed, rounded up to the nearest 5- mph increment, and limiting the speed differential to 10-mph on the upper range and 20-mph for the mid-range.
Every effort should be made to meet the upper range ramp/connector design speed.
Table 9-11
shows the values for ramp/connector design speeds.
Table 9-11: Guide Values for Ramp/Connector Design Speed as Related to Highway Design Speed
1
Ramp/Connector Design Speed
2
 (mph)
Highway Design Speed (mph)
85
90
95
100
Upper Range (85%)
75
80
85
90
Mid-Range (70%)
65
70
75
80
Lower Range (50%)
55
60
65
70
Notes:
  1. Values determined by the percentage of the highway design speed or the max difference between highway and ramp design speed (10 mph for upper, 20 mph for mid, 30 mph for lower), whichever is higher.
  2. For corresponding minimum radius for applicable ramp speed and superelevation rate e-max, see Table 4-6, Table 4-7, Table 9-5 and Table 9-6.

9.4.3 Lane and Shoulder Widths

Ramp and direct connector shoulder widths (inside and outside) and lane widths are shown in
Table 9-12
.
Table 9-12: Ramp and Direct Connector Widths
Number of Lanes
Inside Shoulder
Width (ft)
Outside Shoulder
Width
1
 (ft)
Traffic Lanes (ft)
1
8
10
14
2
4
10
26 (14/12)
Notes:
  1. If sight distance restrictions are present due to horizontal curvature, the shoulder width on the inside of the curve may be increased to 10-ft and the shoulder width on the outside of the curve decreased to 8-ft (one lane) or 4-ft (two lane).

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.

9.4.5 Distance Between Successive Ramps

The minimum acceptable distance between ramps is dependent upon the merge, diverge, and weaving operations that take place between ramps. The
HCM
must be used for analysis of these requirements. Several iterations of the analysis may be required to determine these lengths at the higher design speeds. The distances required for adequate signing must also be considered.

9.4.6 Grades

Grades are associated with the design speed selected for the ramp. Design criteria for design speeds greater than 85-mph can be found in
Table 9-3
.
Section 4.8.1
provides design criteria for speeds less than 85-mph.

9.4.7 Cross Section and Cross Slope

The cross slope for ramp tangent sections should be similar to the cross slope used on the mainlanes of the roadway. The cross slope on the ramp should be sloped in the same direction across the entire ramp. The cross slope used will depend on the pavement type and other drainage considerations.