Federal Stopping Distance Excerpt

Taken from http://www.tfhrc.gov/safety/pubs/04091/03.htm#chp36

3.6 Sight Distance

A driver’s ability to see the road ahead and other intersection users is critical to safe and efficient use of all roadway facilities, especially signalized intersections. Stopping sight distance, decision sight distance, and intersection sight distance are particularly important at signalized intersections.

3.6.1 Stopping Sight Distance

Stopping sight distance is the distance along a roadway required for a driver to perceive and react to an object in the roadway and to brake to a complete stop before reaching that object. Stopping sight distance should be provided throughout the intersection and on each entering and exiting approach. Table 11 gives recommended stopping sight distances for design, as computed from the equations provided in the AASHTO policy.⁽³⁾

Table 11. Design values for stopping sight distance.

Speed (km/h)	Computed Distance* (m)	Design Distance (m)	Speed (mph)	Computed Distance* (ft)	Design Distance (ft)
20	18.5	20	15	76.7	80
30	31.2	35	20	111.9	115
40	46.2	50	25	151.9	155
50	63.5	65	30	196.7	200
60	83.0	85	35	246.2	250
70	104.9	105	40	300.6	305
80	129.0	130	45	359.8	360
90	155.5	160	50	423.8	425
100	184.2	185	55	492.4	495
110	215.3	220	60	566.0	570
120	248.6	250	65	644.4	645
* Assumes 2.5 s perception-braking time, 3.4 m/s² (11.2 ft/s²) driver deceleration Source: Reference 3, exhibit 3-1.

Stopping sight distance should be measured using an assumed height of driver’s eye of 1,080 mm (3.5 ft) and an assumed height of object of 600 mm (2.0 ft).⁽³⁾

3.6.2 Decision Sight Distance

Decision sight distance is “the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete the maneuver safely and efficiently.”^{(3, p. 115)} Decision sight distance at intersections is applicable for situations where vehicles must maneuver into a particular lane in advance of the intersection (e.g., alternative intersection designs using indirect left turns).

Decision sight distance varies depending on whether the driver is to come to a complete stop or make some kind of speed, path, or direction change. Decision sight distance also varies depending on the environment—urban, suburban, or rural. Table 12 gives recommended values for decision sight distance, as computed from equations in the AASHTO policy.⁽³⁾

Table 12. Design values for decision sight distance for selected avoidance maneuvers.

Metric (m)
Speed (km/h)	A	B	C	D	E
50	70	155	145	170	195
60	95	195	170	205	235
70	115	235	200	235	275
80	140	280	230	270	315
90	170	325	270	315	360
100	200	370	315	355	400
110	235	420	330	380	430
120	265	470	360	415	470

U.S. Customary (ft)
Speed (mph)	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

Avoidance Maneuver A: Stop on rural road, time (t) = 3.0 s.

Avoidance Maneuver B: Stop on urban road, t = 9.1 s.

Avoidance Maneuver C: Speed/path/direction change on rural road, t = 10.2 s to 11.2 s.

Avoidance Maneuver D: Speed/path/direction change on suburban road, t = 12.1 s to 12.9 s.

Avoidance Maneuver E: Speed/path/direction change on urban road, t = 14.0 s to 14.5 s.

Source: Reference 3, exhibit 3-3.

******************This is where text goes*********************

POSTED PROBLEMS

We invite you to comment upon these posted problems,
present your ideas and or suggested solutions
please send them to us via email and we will post
a synopsis of your idea, with your byline!
BookMark This Site Now
...We are grateful to Stormynites for their help
with our Organization and encourage you to Promote Stormynites™ Too!

Learn How To

Go to Stormynites™ Main Page

Designed by:

Stormy™

Page under Construction,

--->End of Line<---