The Digital Press

Urban street networks and grid models both show a shift from smooth traffic flow to congestion as vehicle arrival rates increase, with traffic-aware routing helping but not fully preventing jams. A mixed phase with both free flow and congestion appears in naturally developed street layouts.

Why it matters: Understanding congestion emergence aids urban planning and traffic management to reduce delays and economic losses.

The big picture: Both real city streets and idealized grids exhibit similar congestion patterns and phase transitions under varied traffic conditions.

Stunning stat: Small-degree nodes have higher probabilities of extreme traffic events than major hubs in free-flow traffic regimes.

The stakes: Even advanced routing cannot completely eliminate congestion, highlighting limits of traffic control in complex urban networks.