Stopping Sight Distance
Stopping sight distance, abbreviated as SSD, is the distance traveled by a vehical from the time it is observer to the time it comes to a stop.
stopping Sight Distance formulas |
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\(\large{ SSD = 1.47 \; V \; t \;+\; 1.075 \; \frac{ V^2 }{ a } }\) \(\large{ SSD = 1.47 \; V \; t \; \frac{ 1.075 \; V^2 }{ a } }\) \(\large{ SSD = \frac{ 1.47 \; V \; t \;+\; 1.075 \; V^2 }{ a } }\) |
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| Symbol | English | Metric |
| \(\large{ SSD }\) = sight distance for stopping or passing | \(\large{ft}\) | \(\large{m}\) |
| \(\large{ t }\) = brake reaction time | \(\large{sec}\) | \(\large{s}\) |
| \(\large{ a }\) = deceleration rate | \(\large{\frac{ft}{sec^2}}\) | \(\large{\frac{m}{s^2}}\) |
| \(\large{ V }\) = design speed | \(\large{\frac{ft}{sec}}\) | \(\large{\frac{m}{s}}\) |
| \(\large{ G }\) = grade percent divided by 100 | \(\large{dimensionless}\) | |
AASHTO Exhibit 3-1 Stopping Sight Distance |
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| Design Speed |
Design Speed Distance |
Braking Distance on Level | Stopping Sight Distance | |
| Calculated | Design | |||
| 15 | 55.1 | 21.6 | 76.7 | 80 |
| 20 | 73..5 | 38.4 | 111.9 | 115 |
| 25 | 91.9 | 60.0 | 151.9 | 155 |
| 30 | 110.3 | 86.4 | 196.7 | 200 |
| 35 | 128.6 | 117.6 | 246.2 | 250 |
| 40 | 147.0 | 153.6 | 300.6 | 305 |
| 45 | 165.4 | 194.4 | 359.8 | 360 |
| 50 | 183.8 | 240.0 | 423.8 | 425 |
| 55 | 202.1 | 290.3 | 492.4 | 495 |
| 60 | 220.5 | 345.5 | 566.0 | 570 |
| 65 | 238.9 | 4.505 | 644.4 | 645 |
| 70 | 257.3 | 470.3 | 727.6 | 730 |
| 75 | 275.6 | 539.9 | 815.5 | 820 |
| 80 | 294.0 | 614.3 | 908.3 | 910 |
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Note: Brake reaction distance predicated on a time of 2.5 s; deceleration rate of 11.2 \(ft/s^2\) used to determine calculated sight distance. |
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