35 research outputs found
Determination of Interaction Potentials in Freeway Traffic from Steady-State Statistics
Many-particle simulations of vehicle interactions have been quite successful
in the qualitative reproduction of observed traffic patterns. However, the
assumed interactions could not be measured, as human interactions are hard to
quantify compared to interactions in physical and chemical systems. We show
that progress can be made by generalizing a method from equilibrium statistical
physics we learned from random matrix theory. It allows one to determine the
interaction potential via distributions of the netto distances s of vehicles.
Assuming power-law interactions, we find that driver behavior can be
approximated by a forwardly directed 1/s potential in congested traffic, while
interactions in free traffic are characterized by an exponent of approximately
4. This is relevant for traffic simulations and the assessment of telematic
systems.Comment: For related work see http://www.helbing.or
An information-based traffic control in a public conveyance system: reduced clustering and enhanced efficiency
A new public conveyance model applicable to buses and trains is proposed in
this paper by using stochastic cellular automaton. We have found the optimal
density of vehicles, at which the average velocity becomes maximum,
significantly depends on the number of stops and passengers behavior of getting
on a vehicle at stops. The efficiency of the hail-and-ride system is also
discussed by comparing the different behavior of passengers. Moreover, we have
found that a big cluster of vehicles is divided into small clusters, by
incorporating information of the number of vehicles between successive stops.Comment: 8 pages, 15 figure
Application of thermodynamics to driven systems
Application of thermodynamics to driven systems is discussed. As particular
examples, simple traffic flow models are considered. On a microscopic level,
traffic flow is described by Bando's optimal velocity model in terms of
accelerating and decelerating forces. It allows to introduce kinetic,
potential, as well as total energy, which is the internal energy of the car
system in view of thermodynamics. The latter is not conserved, although it has
certain value in any of two possible stationary states corresponding either to
fixed point or to limit cycle in the space of headways and velocities. On a
mesoscopic level of description, the size n of car cluster is considered as a
stochastic variable in master equation. Here n=0 corresponds to the fixed-point
solution of the microscopic model, whereas the limit cycle is represented by
coexistence of a car cluster with n>0 and free flow phase. The detailed balance
holds in a stationary state just like in equilibrium liquid-gas system. It
allows to define free energy of the car system and chemical potentials of the
coexisting phases, as well as a relaxation to a local or global free energy
minimum. In this sense the behaviour of traffic flow can be described by
equilibrium thermodynamics. We find, however, that the chemical potential of
the cluster phase of traffic flow depends on an outer parameter - the density
of cars in the free-flow phase. It allows to distinguish between the traffic
flow as a driven system and purely equilibrium systems.Comment: 9 pages, 6 figures. Eur. Phys. J. B (2007) to be publishe