At-grade intersection design covers channelization, turn lanes, corner radii, and sight triangles. Left-turn lanes are warranted per AASHTO guidelines when the design hourly volume exceeds 100 left-turning vehicles or the through volume exceeds 300 vph. Right-turn deceleration lanes are warranted when the turning volume exceeds 50 vph on roads with design speed ≥50 mph. Corner radii: minimum 25 ft for residential, 30-40 ft for collectors, 50 ft for arterials serving trucks/buses.
References: AASHTO current edition, AZ Standard Specifications, FHWA Technical Advisories, and applicable federal regulations (23 CFR). Contractors shall maintain current copies of all referenced standards on the project site.
Source: ADOT Highway Design Manual, 2024 Edition. Pages 15–16 of 37.