Modeling traffic flow transition and breakdown processes on congested freeways

The dissertation investigates the behavior of traffic flow characteristics over time on congested freeways and identifies transition processes between the traffic flow regimes, dense congested stable (DCS) flow and breakdown flow. This investigation is conducted by calibrating models in the Density-Time plane and by experimental results in the Speed-Time plane. The models which are based on statistical physics theory and previous non-traffic engineering experience (stock crashes, earthquakes) are applied to real traffic data from Interstate 66 in Virginia.; It was found that the Density-Time models, which replicate the concept of collective behavior of drivers by the mathematical property of log periodic oscillations (LPO), properly reflect the phase transition in freeway traffic flow. The parameter Tc, which signifies the time of a crash of the stock market or occurrence of large earthquake, does not indicate the time of breakdown flow conditions (LOS F). Breakdown occurrence was revealed by the cyclic properties of the LPO models following the DCS flow regime. The inflection point of the first LPO cycle that follows the DCS flow regime starts the "critical transition period". This point that is identified when the density slope line reaches its maximum, leads to the breakdown flow conditions after 5--8 minutes when the density reaches its maximum. The average maximum slope for three typical days studied was 2.75 vehicles per mile per lane (vpmpl) per minute. At the maximum slope the average density was 56 vpmpl. This was 20% less than the average maximum density that indicates breakdown flow conditions. Practically, the LPO models lack in prediction power for anticipating breakdown occurrence.; Experimental design techniques showed in this dissertation that transition times toward breakdown are significantly affected by location when a single breakdown period is experienced. The transition velocities that are supported by shockwave calculations clarify spatial evolution of traffic breakdown and assist to identify the major breakdown source. Additionally, GIS time-based approach helps the traffic control centers visualize traffic conditions in a format that is comprehensible to the public and as a result track breakdowns' spatial evolution. Further research on additional congested freeway sections that experience different peak day periods, is suggested.