  The dynamical properties of road traffic time series from North-Rhine
Westphalian motorways are investigated. The article shows that road traffic
dynamics is well described as a persistent stochastic process with two fixed
points representing the freeflow (non-congested) and the congested state
regime. These traffic states have different statistical properties, with
respect to waiting time distribution, velocity distribution and
autocorrelation. Logdifferences of velocity records reveal non-normal,
obviously leptocurtic distribution. Further, linear and nonlinear phase-plane
based analysis methods yield no evidence for any determinism or deterministic
chaos to be involved in traffic dynamics on shorter than diurnal time scales.
Several Hurst-exponent estimators indicate long-range dependence for the free
flow state. Finally, our results are not in accordance to the typical heuristic
fingerprints of self-organized criticality. We suggest the more simplistic
assumption of a non-critical phase transition between freeflow and congested
traffic.
