Roadway Geometric Design: stopping_sight_distance
AASHTO Green Book 7th Edition (2018) roadway geometric design standards — stopping sight distance (15–80 mph), passing sight distance (20–70 mph), minimum horizontal curve radius by design speed and emax (4%/6%/8%), K-values for crest and sag vertical curves (25–80 mph), maximum grade limits by terrain type (level/rolling/mountainous) and road class (freeway/arterial/collector/local), superelevation standards, lane and shoulder width standards, and design vehicle dimensions (P, SU, WB-40, WB-62, WB-67).
| parameter type | record id | description | design speed mph (mph) | notes | unit | value min (varies) | value typical (varies) |
|---|---|---|---|---|---|---|---|
| stopping_sight_distance | ssd_15 | Stopping sight distance — 15 mph design speed | 15 | SSD = 0.278*V*t + V^2/(254*a); t=2.5s PRTD, a=3.4 m/s2; eye ht 3.5ft, object ht 2.0ft | ft | 80 | 80 |
| stopping_sight_distance | ssd_20 | Stopping sight distance — 20 mph design speed | 20 | Per AASHTO 2018 Table 3-1; perception-reaction time 2.5 s, a=11.2 ft/s2 | ft | 115 | 115 |
| stopping_sight_distance | ssd_25 | Stopping sight distance — 25 mph design speed | 25 | Per AASHTO 2018 Table 3-1 | ft | 155 | 155 |
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