Physics of traffic gridlock in a city

Area of Science:

• Traffic flow dynamics
• Urban transportation systems
• Stochastic modeling

Background:

• Signalized intersections are critical urban infrastructure.
• Traffic flow models predict congestion based on inflow and signal timing.
• Understanding spontaneous breakdown is key to mitigating gridlock.

Purpose of the Study:

• To investigate the conditions leading to spontaneous traffic breakdown at signalized intersections.
• To analyze the probability of traffic gridlock under specific flow conditions.
• To identify factors influencing traffic breakdown initiation.

Main Methods:

• Simulations using stochastic three-phase and two-phase traffic flow models.
• Analysis of traffic dynamics under varying link inflow rates and signal phases.
• Examination of phase transitions from free flow to synchronized flow.

Main Results:

• Spontaneous traffic breakdown and gridlock can occur even when queues are expected to dissipate.
• Breakdown is often initiated by a phase transition to synchronized flow upstream of the intersection.
• The probability of breakdown increases with higher link inflow rates and longer red light durations.

Conclusions:

• Traffic gridlock at signalized intersections can arise unpredictably.
• Flow dynamics upstream of the queue significantly influence breakdown.
• Inflow rate and red phase duration are critical parameters affecting gridlock probability.