Sight Distance Guidelines

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Sight Distance Guidelines

Transcript Of Sight Distance Guidelines

SIGHT DISTANCE GUIDELINES
According to the 2011 AASHTO, 2011 MMUTCD, and Michigan Department of Transportation Guidelines
PREPARED BY GEOMETRICS AND OPERATIONS UNIT
TRAFFIC AND SAFETY April 22, 2015
“Providing the highest quality transportation services for economic benefit and improved quality of life.”

INDEX
PAGE NUMBER ACKNOWLEDGEMENTS ...............................................................................................iii
TYPES OF SIGHT DISTANCE....................................................................................... iii
STOPPING SIGHT DISTANCE ...................................................................................... 1 Quick Charts for Stopping Sight Distance .............................................................. 3 STOPPING SIGHT DISTANCE ................................................................................... 5 Horizontal Stopping Sight Distance......................................................................... 6 Vertical Curves ........................................................................................................ 10 Crest Vertical Curves .............................................................................................. 11 Sag Vertical Curves ................................................................................................. 13 Design Controls: Stopping Sight Distance .......................................................... 16 General Control for Vertical Alignment ................................................................. 18
PASSING SIGHT DISTANCE ....................................................................................... 19 Quick Charts for Passing Sight Distance .............................................................. 21 PASSING SIGHT DISTANCE (Two-Lane, Two-Way Highways) ............................ 23 Measurement of Passing Sight Distance.................................................... .......... 24 Passing Sight Distance on Multilane Roadways................................................... 25 Passing Sight Distance for Horizontal Curves...................................................... 25 Passing Sight Distance for Vertical Curves .......................................................... 26 Passing Sight Distance - Pavement Markings ...................................................... 27
DECISION SIGHT DISTANCE...................................................................................... 30 Quick Chart for Decision Sight Distance ............................................................... 31 DECISION SIGHT DISTANCE .................................................................................. 33
INTERSECTION SIGHT DISTANCE ............................................................................ 37 Quick Charts for Intersection Sight Distance ....................................................... 39 INTERSECTION SIGHT DISTANCE......................................................................... 41 Intersections with Stop-Control on the Minor Road ............................................. 42 Intersection Sight Distance Considerations for Signalized Intersections .......... 48 Determination and Measurement of Intersection Sight Distance........................ 48 Field Measurement of Intersection Sight Distance............................................... 51
REFERENCES.............................................................................................................. 52

MDOT Traffic & Safety

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PW Ref Docs\T&S\Typicals\Final\Geometrics\mdot_Guidelines_Sight_Distance.doc

April 22, 2015

MDOT Traffic & Safety

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PW Ref Docs\T&S\Typicals\Final\Geometrics\mdot_Guidelines_Sight_Distance.doc

April 22, 2015

ACKNOWLEDGEMENTS
The Michigan Department of Transportation (MDOT) practices regarding sight distance measurement are based almost exclusively and entirely upon the AASHTO sight distance principles, theories, and methodologies. Therefore, it was not possible to produce this reference document without utilizing significant portions of the A Policy on Geometric Design of Highways and Streets, 2011, by the American Association of State Highway and Traffic Officials (AASHTO), Washington, D.C. MDOT would like to acknowledge the AASHTO publication (used by permission) as the major source material within this document. As a result, several sections of the AASHTO publication were incorporated into this document, either directly and intact, or paraphrased for ease of explanation and/or understanding. Acknowledgements are also extended to the Michigan Manual on Uniform Traffic Control Devices (MMUTCD), 2011 Edition, for additional source material.
In general, the information in this document can be found in Chapters 3 and 9 of the AASHTO publication, and in Part 3 of the MMUTCD publication. For all references used in this guide, the document and page number is provided, i.e.
(2011 AASHTO, 3-1).
TYPES OF SIGHT DISTANCE
“Sight distance is the distance along a roadway throughout which an object of specified height is continuously visible to the driver. This distance is dependent on the height of the driver’s eye above the road surface, the specified object height above the road surface, and the height and lateral position of sight obstructions within the driver’s line of sight.” (2011 AASHTO, 3-14)
Following are the four types of sight distance:
• Stopping Sight Distance
• Passing Sight Distance
• Decision Sight Distance
• Intersection Sight Distance
Each of the different types of sight distance will be further detailed in the next four sections.

MDOT Traffic & Safety

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STOPPING SIGHT
DISTANCE

MDOT Traffic & Safety

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Quick Charts for Stopping Sight Distance

Design

Stopping Rate of Vertical Curvature, K*

Speed (mph)

Sight Distance (ft)

Calculated

Design

15

80

3.0

3

20

115

6.1

7

25

155

11.1

12

30

200

18.5

19

35

250

29.0

29

40

305

43.1

44

45

360

60.1

61

50

425

83.7

84

55

495

113.5

114

60

570

150.6

151

65

645

192.8

193

70

730

246.9

247

75

820

311.6

312

80

910

383.7

384

Design Controls for Stopping Sight Distance and Crest Vertical Curves

(2011 AASHTO, Exhibit 3-34, 3-155)

Design

Stopping Rate of Vertical Curvature, K*

Speed (mph)

Sight Distance (ft)

Calculated

Design

15

80

9.4

10

20

115

16.5

17

25

155

25.5

26

30

200

36.4

37

35

250

49.0

49

40

305

63.4

64

45

360

78.1

79

50

425

95.7

96

55

495

114.9

115

60

570

135.7

136

65

645

156.5

157

70

730

180.3

181

75

820

205.6

206

80

910

231.0

231

Design Controls for Stopping Sight Distance and Sag Vertical Curves
(2011, AASHTO, Exhibit 3-36, 3-161)

*Rate of vertical curvature, K, is the length of curve (L) per percent Algebraic difference on intersecting grades (A). K= L/A

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