Roadway Geometric Design: superelevation
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 | notes | unit | value max (varies) | value min (varies) | value typical (varies) |
|---|---|---|---|---|---|---|---|
| superelevation | emax_high_snowice | Maximum superelevation emax — snow and ice region | AASHTO Green Book 7th Ed 2018 Sec.3.3.2 | emax limited to 6% in regions with frequent snow and ice | % | 6 | 6 |
| superelevation | emax_rural_high_speed | Maximum superelevation emax — rural high-speed highway | AASHTO Green Book 7th Ed 2018 Sec.3.3.2 | emax = 8% standard for rural highways; balances vehicle dynamics and snow/ice conditions | % | 8 | 8 |
| superelevation | emax_urban | Maximum superelevation emax — urban/suburban | AASHTO Green Book 7th Ed 2018 Sec.3.3.2 | emax = 4% for constrained urban conditions (parking, pedestrians); emax = 6% moderate urban | % | 4 | 6 |
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