Page 103 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

86 CHAPTER TWO

TABLE 2.4 Decision Sight Distance (DSD) for Design Speeds from 30 to 70 mi/h
(48 to 113 km/h)
Decision sight distance, ft
Avoidance maneuver
Design speed, mi/h A B C D E
30 220 490 450 535 620
35 275 590 525 625 720
40 330 690 600 715 825
45 395 800 675 800 930
50 465 910 750 890 1030
55 535 1030 865 980 1135
60 610 1150 990 1125 1280
65 695 1275 1050 1220 1365
70 780 1410 1105 1275 1445
● The avoidance maneuvers are as follows: A—rural stop; B—urban stop; C—rural
speed/path/direction change; D—suburban speed/path/direction change; E—urban
speed/path/direction change
● Decision sight distance (DSD) is calculated or measured using the same criteria as
stopping sight distance: 3.50 ft (1.07 m) eye height and 2.00 ft (0.61 m) object height.
Conversions: 1 mi/h 1.609 km/h, 1 ft 0.305 m.
Source: Location and Design Manual, Vol. 1, Roadway Design, Ohio Department of
Transportation, with permission.
TABLE 2.5 Maximum Centerline Deflection Not
Requiring a Horizontal Curve
Design speed, mi/h Maximum deflection*
25 5°30´
30 3°45´
35 2°45´
40 2°15´
45 1°45´
50 1°15´
55 1°00´
60 1°00´
65 0°45´
70 0°45´
Based on the following formulas:
Design speed 50 mi/h or over: tan
1.0/V
Design speed under 50 mi/h: tan
60/V 2
where V design speed, mi/h

deflection angle
Conversions: 1 mi/h 1.609 km/h, 1 ft 0.305 m.
Note: The recommended minimum distance between
consecutive horizontal deflections is:
200 ft where design speed 45 mi/h
100 ft where design speed 45 mi/h
*Rounded to nearest 15 min.
Source: Location and Design Manual, Vol. 1, Roadway
Design, Ohio Department of Transportation, with permission.