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Section 4: Ramps and Direct Connections

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Overview

Ramps and direct connections are designed to the same criteria. Subsequent discussions referring to ramps shall be construed to also include and apply to direct connections.

This subsection discusses ramps and direct connections and includes information on the following topics:

  • Design Speed
  • Lane and Shoulder Widths
  • Acceleration and Deceleration Lengths
  • Distance Between Successive Ramps
  • Grades and Profiles
  • Cross Section and Cross Slopes
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Design Speed

Similar to facilities with design speeds of 80 mph [130 km/h] or less, ramps on these facilities should also have a relationship between the ramp design speed and the mainlane design speed. The current relationship, in general, is for the ramp design speed to be 85 or 70 percent of the highway design speed, rounded up to the nearest 5 mph [10 km/h] increment, and limiting the speed differential to 10 mph [20 km/h] on the upper range and 20 mph [30 km/h] for the mid range.

Table 8-12 shows the values for ramp/connector design speeds.

NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018261Table 8-12: Guide Values for Ramp/Connection Design Speed as Related to Highway Design Speed1

(US Customary)

-

Highway Design Speed (mph)

85

90

95

100

Ramp Design Speed (mph):

-

Upper Range (85%)

75

80

85

90

Mid Range (70%)

65

70

75

80

(Metric)

-

Highway Design Speed (km/h)

140

150

160

Ramp Design Speed (km/h)

-

Upper Range (85%)

120

130

140

Mid Range (70%)

110

120

130

1 Values determined by calculating the 85 or 70 % value of the highway design speed and rounding up to the nearest 5 mph [10 km/h] increment and then adjusting if the rounded value is more than the cap amount from the highway design speed (10 mph [20 km/h] for upper range and 20 mph [30 km/h]for mid range).



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Lane and Shoulder Widths

Ramp and Direct Connection shoulder widths (inside and outside) and lane widths are shown in Table 8-13.

NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018369Table 8-13: Ramp and Direct Connection Widths (US Customary)

-

Inside Shoulder Width (ft)

Outside Shoulder Width1 (ft)

Traffic Lanes(ft)

1-lane

8

10

14

2-lane

4

10

26

(Metric)

-

Inside Shoulder Width (m)

Outside Shoulder Width1 (m)

Traffic Lanes (m)

1-lane

2.4

3.0

4.3

2-lane

1.2

3.0

7.9

1If sight distance restrictions are present due to horizontal curvature, the shoulder width on the inside of the curve may be increased to 10 ft [3.0 m] and the shoulder width on the outside of the curve decreased to 8 ft [2.4 m] (one lane) or 4 ft [1.2 m] (two lane).



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Acceleration and Deceleration Lengths

Table 8-14 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.

Table 8-15 provides design criteria for entrance ramp acceleration and taper lengths; adjustment factors for grade effects are shown in Table 8-16.

NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018413Table 8-14: Lengths of Exit Ramp Speed Change Lanes (US Customary)

Highway Design Speed (mph)

Minimum Length of Taper, T (ft)

Deceleration Length, D (ft) for Exit Curve Design Speed (mph)

Stop

15

20

25

30

35

40

45

50

55

60

65

70

75

Assumed Exit Curve Speed (mph)

0

14

18

22

26

30

36

40

44

48

52

55

58

61

30

35

40

45

50

55

60

65

70

75

Existing Criteria in Roadway Design Manual Figure 3-36

--

--

--

--

--

--

185

225

270

310

--

--

--

--

--

--

--

185

225

265

--

--

--

--

--

--

--

--

190

235

--

--

--

--

--

--

--

--

--

195

--

--

--

--

--

--

--

--

--

--

80

335

310

275

240

200

85

90

95

100

345

360

370

425

650

695

780

900

630

675

760

880

615

660

745

865

595

645

725

850

575

625

705

830

550

600

680

805

510

555

640

760

475

525

605

730

440

490

570

695

355

400

450

530

655

310

355

405

485

610

275

325

370

455

575

240

285

335

415

540

200

250

295

375

500

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 and to consider the taper as part of the deceleration length.



NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018617Table 8-14: Lengths of Exit Ramp Speed Change Lanes (Metric)

Highway Design Speed (km/h

Minimum Length of Taper, T (m)

Deceleration Length, D (m) for Exit Curve Design Speed (km/h)

Stop

20

30

40

50

60

70

80

90

100

110

120

Assumed Exit Curve Speed (km/h)

0

20

28

35

42

51

63

70

77

85

91

98

50

60

70

80

90

100

110

120

Existing Criteria in Roadway Design Manual Figure 3-36

--

--

--

--

--

56

78

102

--

--

--

--

--

--

52

78

--

--

--

--

--

--

--

58

--

--

--

--

--

--

--

--

130

116

92

73

--

140

150

160

110

115

130

248

271

309

241

264

303

234

258

297

226

250

290

217

241

282

202

227

268

178

204

248

162

189

233

144

172

216

121

150

196

103

132

180

80

110

159

NOTE: Where providing desirable deceleration length is impractical, it is acceptable to allow for a moderate amount of deceleration (15 km/h) within the through lanes and to consider the taper as part of the deceleration length.



NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018741Table 8-15: Lengths of Entrance Ramp Speed Change Lanes (US Customary)

Highway Design Speed (mph)

Minimum Length of Taper, T (ft)

Acceleration Length, A (ft) for Entrance Curve Design Speed (mph)

Stop

15

20

25

30

35

40

45

50

55

60

65

70

75

Initial Speed (mph)

0

14

18

22

26

30

36

40

44

48

52

55

58

30

35

40

45

50

55

60

65

70

75

Existing Criteria in

Roadway Design Manual Figure 3-36

--

--

--

--

--

--

--

132

331

545

--

--

--

--

--

--

--

--

70

287

--

--

--

--

--

--

--

--

--

74

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

80

771

516

306

79

--

85

90

95

100

345

360

370

425

2186

2403

2786

3372

2154

2379

2777

3385

2045

2266

2658

3256

2006

2233

2636

3250

1945

2179

2593

3225

1828

2065

2484

3123

1601

1840

2264

2910

1426

1668

2097

2751

1227

1472

1906

2568

1009

1259

1701

2375

757

1010

1459

2142

550

805

1258

1949

326

584

1042

1740

84

345

808

1514

NOTE: Uniform 50:1 to 70:1 tapers are recommended where lengths of acceleration lanes exceed 1,300 ft.



NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1018881Table 8-15: Lengths of Entrance Ramp Speed Change Lanes (Metric)

Highway Design Speed (km/h

Minimum Length of Taper, T (m)

Acceleration Length, A (m) for Entrance Curve Design Speed (km/h)

Stop

20

30

40

50

60

70

80

90

100

110

120

Initial Speed (km/h)

0

20

30

40

47

55

63

70

77

85

91

98

50

60

70

80

90

100

110

120

Existing Criteria in Roadway Design Manual Figure 3-36

--

--

--

--

--

--

48

156

--

--

--

--

--

--

--

46

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

130

218

109

--

--

140

150

160

110

115

130

703

819

977

687

806

987

793

945

652

776

940

624

750

928

572

700

877

507

646

787

438

581

726

350

492

657

245

392

570

155

305

496

37

190

397

Note: Uniform 50:1 to 70:1 tapers are recommended where lengths of acceleration lanes exceed 400 m.



NOTE: Online users can click here to see the below table in PDF format.

Anchor: #i1019061Table 8-16: Speed Change Lane Adjustment Factors as a Function of a Grade (US Customary)

Design Speed of Roadway (mph)

Ratio of Length on Grade to Length on Level1

20

25

30

35

40

45

50

All Speeds

3 to 4% Upgrade

3 to 4% Downgrade

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 % Downgrade

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

(Metric)

Design Speed of Roadway (km/h)

Ratio of Length on Grade to Length on Level1

40

50

60

70

80

All Speeds

3 to 4% Upgrade

3 to 4% Downgrade

140

150

160

1.57

1.60

1.63

1.67

1.70

1.73

1.81

1.86

1.90

1.79

1.83

1.86

1.90

1.94

1.99

0.55

0.53

0.52

5 to 6 % Upgrade

5 to 6 % Downgrade

140

150

160

2.55

2.70

2.86

2.82

3.00

3.18

3.53

3.81

4.09

3.92

4.29

4.65

4.42

4.88

5.34

0.44

0.42

0.41

1 Ratio in this table multiplied by length of acceleration distances gives length of acceleration distance on grade.



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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 the Highway Capacity Manual should 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 should also be considered.

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Grades and Profiles

Grades and profiles are associated with design speed selected for the ramp. Design criteria for design speeds less than 85 mph [140km/h] can be found in Chapter 2.

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Cross Section and Cross Slopes

The cross slope for ramp tangent sections should be similar to the cross slope used on the main lanes 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 used and other drainage considerations.

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