Acceleration and Deceleration Lengths

7/27/2019 Acceleration and Deceleration Lengths

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http://onlinemanuals.txdot.gov/txdotmanuals/rdw/ramps_and_direct_connections.htm

Design Speed

Similar to facilities with design speeds of 80 mph [130 km/h] or less, ramps on these facilities should also have a relationshipbetween 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 clickhereto see the below table in PDF format.

Table 8-12: Guide Values for Ramp/Connection Design Speed as Related to Highway Design Speed

(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
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/ramps_and_direct_connections.htmhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/ramps_and_direct_connections.htmhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-12.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-12.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-12.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-12.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/ramps_and_direct_connections.htm


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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).

Lane and Shoulder Widths

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


Table 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).

Acceleration and Deceleration Lengths
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-13.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-13.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-13.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-13.pdf


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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.


Table 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

6570

75

Existing Criteria inRoadway Design Manual Figure 3-36 --

--

--

--

--

--

185

225270

310

--

--

--

--

--

--

--

185225

265

--

--

--

--

--

--

--

--190

235

--

--

--

--

--

--

--

----

195

--

--

--

--

--

--

--

----

--

80 335 310 275 240 200

85

90

95

345

360

370

650

695

780

630

675

760

615

660

745

595

645

725

575

625

705

550

600

680

510

555

640

475

525

605

440

490

570

355

400

450

310

355

405

275

325

370

240

285

335

200

250

295


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100 425 900 880 865 850 830 805 760 730 695 530

655

485

610

455

575

415

540

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.


Table 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 inRoadway Design Manual Figure 3-36 --

--

--

--

--

56

78

102

--

--

--

--

--

--

52

78

--

--

--

--

--

--

--

58

--

--

--

--

--

--

--

--

130 116 92 73 --

140

150

110

115

248

271

241

264

234

258

226

250

217

241

202

227

178

204

162

189

144

172

121

150

103

132

80

110
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-14.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-14.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-14.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-14.2.pdf


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160 130 309 303 297 290 282 268 248 233 216 196 180 159

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.


Table 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 --

85 345 2186 2154 2045 2006 1945 1828 1601 1426 1227 1009 757 550 326 84


6/9

90

95

100

360

370

425

2403

2786

3372

2379

2777

3385

2266

2658

3256

2233

2636

3250

2179

2593

3225

2065

2484

3123

1840

2264

2910

1668

2097

2751

1472

1906

2568

1259

1701

2375

1010

1459

2142

805

1258

1949

584

1042

1740

345

808

1514

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


Table 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

110

115

703

819

687

806

793

945

652

776

624

750

572

700

507

646

438

581

350

492

245

392

155

305

37

190
http://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-15.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-15.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-15.2.pdfhttp://onlinemanuals.txdot.gov/txdotmanuals/rdw/table8-15.2.pdf


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160 130 977 987 940 928 877 787 726 657 570 496 397

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


Table 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


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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

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

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.

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.

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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Acceleration and Deceleration Lengths