What are the key design principles for modern roundabouts?

Modern roundabout design principles: (1) Deflection - entry geometry forces speed reduction, (2) Single-lane entries preferred for safety and simplicity, (3) Inscribed circle diameter sized for design vehicle, (4) Splitter islands separate entry/exit and provide pedestrian refuge, (5) Approach curvature achieves target entry speed (25-35 km/h), (6) Central island typically raised, may have truck apron, (7) Adequate sight distance to circulating vehicles. Design balances capacity (larger roundabout) with safety (smaller, more deflection). HCM provides capacity methods.