Roadway Geometric Design: horizontal_curve_emax4
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) |
|---|---|---|---|---|---|---|---|
| horizontal_curve_emax4 | hc_e4_30 | Min horizontal curve radius — 30 mph emax 4% | 30 | Rmin emax=4%; conservative (e.g., flat terrain urban); per AASHTO 2018 Table 3-5 | ft | 360 | 360 |
| horizontal_curve_emax4 | hc_e4_40 | Min horizontal curve radius — 40 mph emax 4% | 40 | Rmin emax=4%, f_s=0.23 at 40 mph | ft | 660 | 660 |
| horizontal_curve_emax4 | hc_e4_50 | Min horizontal curve radius — 50 mph emax 4% | 50 | Rmin emax=4%, f_s=0.19 at 50 mph | ft | 1,190 | 1,190 |
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