Horizontal alignment design shall follow AASHTO Green Book criteria for design speed, radius, superelevation, and sight distance. Minimum curve radius is determined by the design speed and maximum superelevation rate. CDOT uses a maximum superelevation rate of 10% for rural highways and 4% for urban facilities. Compound curves require a ratio of long radius to short radius not exceeding 1.5:1. Broken-back curves (closely spaced curves in the same direction) are discouraged per CO design policy.
References: AASHTO current edition, CO 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: CDOT Highway Design Manual, 2024 Edition. Pages 5–6 of 37.