4 research outputs found
Economics-Based Optimization of Unstable Flows
As an example for the optimization of unstable flows, we present an
economics-based method for deciding the optimal rates at which vehicles are
allowed to enter a highway. It exploits the naturally occuring fluctuations of
traffic flow and is flexible enough to adapt in real time to the transient flow
characteristics of road traffic. Simulations based on realistic parameter
values show that this strategy is feasible for naturally occurring traffic, and
that even far from optimality, injection policies can improve traffic flow.
Moreover, the same method can be applied to the optimization of flows of gases
and granular media.Comment: Revised version of ``Optimizing Traffic Flow'' (cond-mat/9809397).
For related work see http://www.parc.xerox.com/dynamics/ and
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Traffic flow on realistic road networks with adaptive traffic lights
We present a model of traffic flow on generic urban road networks based on
cellular automata. We apply this model to an existing road network in the
Australian city of Melbourne, using empirical data as input. For comparison, we
also apply this model to a square-grid network using hypothetical input data.
On both networks we compare the effects of non-adaptive vs adaptive traffic
lights, in which instantaneous traffic state information feeds back into the
traffic signal schedule. We observe that not only do adaptive traffic lights
result in better averages of network observables, they also lead to
significantly smaller fluctuations in these observables. We furthermore compare
two different systems of adaptive traffic signals, one which is informed by the
traffic state on both upstream and downstream links, and one which is informed
by upstream links only. We find that, in general, both the mean and the
fluctuation of the travel time are smallest when using the joint
upstream-downstream control strategy.Comment: 41 pages, pdflate
Coherent Moving States in Highway Traffic (Originally: Moving Like a Solid Block)
Recent advances in multiagent simulations have made possible the study of
realistic traffic patterns and allow to test theories based on driver
behaviour. Such simulations also display various empirical features of traffic
flows, and are used to design traffic controls that maximise the throughput of
vehicles in heavily transited highways. In addition to its intrinsic economic
value, vehicular traffic is of interest because it may throw light on some
social phenomena where diverse individuals competitively try to maximise their
own utilities under certain constraints.
In this paper, we present simulation results that point to the existence of
cooperative, coherent states arising from competitive interactions that lead to
a new phenomenon in heterogeneous highway traffic. As the density of vehicles
increases, their interactions cause a transition into a highly correlated state
in which all vehicles practically move with the same speed, analogous to the
motion of a solid block. This state is associated with a reduced lane changing
rate and a safe, high and stable flow. It disappears as the vehicle density
exceeds a critical value. The effect is observed in recent evaluations of Dutch
traffic data.Comment: Submitted on April 21, 1998. For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://www.parc.xerox.com/dynamics
Optimised Traffic Flow at a Single Intersection: Traffic Responsive signalisation
We propose a stochastic model for the intersection of two urban streets. The
vehicular traffic at the intersection is controlled by a set of traffic lights
which can be operated subject to fix-time as well as traffic adaptive schemes.
Vehicular dynamics is simulated within the framework of the probabilistic
cellular automata and the delay experienced by the traffic at each individual
street is evaluated for specified time intervals. Minimising the total delay of
both streets gives rise to the optimum signalisation of traffic lights. We
propose some traffic responsive signalisation algorithms which are based on the
concept of cut-off queue length and cut-off density.Comment: 10 pages, 11 eps figs, to appear in J. Phys.