Roadway Design Manual: Ramps and Direct Connectors

Similar to facilities with design speeds of 80-mph or less, ramps on these facilities must also 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 desirable ramp/connector design speed.

Table 8-10 shows the values for ramp/connector design speeds.

Anchor: #i1018261Table 8-10: Guide Values for Ramp/Connector Design Speed as Related to Highway Design Speed¹
Ramp/Connector Design Speed² (mph)	Highway Design Speed (mph)
Ramp/Connector Design Speed² (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: 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. For corresponding minimum radius, see Table 2-4, Table 2-5, Table 8-4 and Table 8-5.

Anchor: #i1026140

Lane and Shoulder Widths

Ramp and direct connector shoulder widths (inside and outside) and lane widths are shown in Table 8-11.

Anchor: #i1018369Table 8-11: Ramp and Direct Connection Widths
Number of Lanes	Inside Shoulder Width (ft)	Outside Shoulder Width¹ (ft)	Traffic Lanes (ft)
1	8	10	14
2	4	10	26 (14/12)
Note: 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).

Anchor: #i1026149

Acceleration and Deceleration Lengths

Table 8-12 provides design criteria for exit ramp deceleration and taper lengths. Adjustment factors for grade effects are independent of highway design speed, therefore use Table 3-14 for deceleration length adjustment factors.

Anchor: #i1264584Table 8-12: 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 Length¹, 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
Note: 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 8-13 provides design criteria for entrance ramp acceleration and taper lengths; adjustment factors for grade effects are shown in Table 8-14.

Anchor: #i1263370Table 8-13: 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)	Deceleration 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	-	-

Anchor: #i1019061Table 8-14: Speed Change Lane Adjustment Factors as a Function of a Grade
Highway Design Speed, V (mph)	Ratio of Length on Grade to Length on Level¹
	3 to 4 % Upgrade		3 to 4 % Downgrade		5 to 6 % Upgrade		5 to 6 % Downgrade
All	0.90		1.20		0.80		1.35
Acceleration Lanes
Highway Design Speed, V (mph)	Ratio of Length on Grade for Design Speed (mph) of Turning Roadway Curve¹
	20	25	30	35	40	45	50	All Speeds
	3 to 4% Upgrade							3 to 4%
85 90 95 100	1.62 1.66 1.71 1.75	1.69 1.73 1.78 1.83	1.75 1.80 1.85 1.90	1.80 1.86 1.92 1.98	1.89 1.96 2.03 2.10	1.99 2.08 2.17 2.26	2.10 2.20 2.30 2.40	0.56 0.55 0.54 0.52
	5 to 6 % Upgrade							5 to 6 %
85 90 95 100	2.39 2.50 2.62 2.74	2.51 2.64 2.76 2.89	2.64 2.77 2.91 3.04	2.94 3.10 3.27 3.43	3.15 3.33 3.51 3.69	3.73 4.00 4.26 4.53	4.28 4.65 5.03 5.40	0.46 0.45 0.44 0.42
Note: Ratio in this table multiplied by length of deceleration or acceleration distances in Table 8-13 and Table 3-14 gives length of deceleration/acceleration distance on grade.

Anchor: #i1026163

Distance Between Successive Ramps

The minimum acceptable distance between ramps is dependent upon the merge, diverge, and weaving operations that take place between ramps and TRB’s Highway Capacity Manual 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.

Anchor: #i1026173

Grades and Profiles

Grades and profiles are associated with the design speed selected for the ramp. Design criteria for design speeds less than 85-mph can be found in Chapter 2 Table 2-9.

Anchor: #i1026183

Cross Section and Cross Slopes

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.