Transportation Science
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Average Delay at an Unsignalized Intersection with Two Major Streams Each Having a Dichotomized Headway Distribution
Transportation Science - Tập 20 Số 4 - Trang 272-286 - 1986
The average time a driver has to wait before he can cross two major streams has
been a major performance indicator for unsignalized intersections. The equations
presented in this paper give an estimate of this average delay as a function of
the average delay to isolated minor stream vehicles (Adams' delay) and the
degree of saturation of the minor stream (minor stream entry flow/maximum entry
flow...
Perceptual Thresholds in Car-Following—A Comparison of Recent Measurements with Earlier Results
Transportation Science - Tập 11 Số 1 - Trang 60-72 - 1977
The authors have previously conducted a field experiment to investigate the
sensitivity of subjects to the sign of relative motion when following a vehicle.
They interpreted their results in terms of responses to analytical functions of
relative speed divided by spacing, or spacing change divided by spacing. In the
present paper the remits of a number of other field, simulator, and laboratory
expe...
Characterizing Traffic Conditions in Urban Areas
Transportation Science - Tập 18 Số 2 - Trang 101-140 - 1984
A series of vehicular traffic experiments conducted in Austin, Texas, shows the
reasonableness of the two assumptions in the two-fluid (moving and stopped
vehicles) model of town traffic. The observational data support the assumption
that the average speed in an urban street network is proportional to the
fraction of the vehicles moving raised to a power and is also in agreement with
the suppositi...
An Adaptive Dynamic Programming Algorithm for Dynamic Fleet Management, I: Single Period Travel Times
Transportation Science - Tập 36 Số 1 - Trang 21-39 - 2002
We consider a stochastic version of a dynamic resource allocation problem. In
this setting, reusable resources must be assigned to tasks that arise randomly
over time. We solve the problem using an adaptive dynamic programming algorithm
that uses nonlinear functional approximations that give the value of resources
in the future. Our functional approximations are piecewise linear and naturally
prov...
Vehicle Routing with Stochastic Demands: Properties and Solution Frameworks
Transportation Science - Tập 23 Số 3 - Trang 166-176 - 1989
This paper considers the vehicle routing problem with stochastic demands. The
objective is to provide an overview of this problem, and to examine a variety of
solution methodologies. The concepts and the main issues are reviewed along with
some properties of optimal solutions. The existing stochastic mathematical
programming formulations are presented and compared and a new formulation is
proposed...
Computational Approaches to Stochastic Vehicle Routing Problems
Transportation Science - Tập 29 Số 4 - Trang 342-352 - 1995
We report computational test results for several graph-based a priori heuristics
for the Euclidean plane versions of two well-known stochastic optimization
problems, the probabilistic traveling salesman problem (PTSP) and the
probabilistic (or stochastic) vehicle routing problem (PVRP). These heuristics
are termed a priori because they design vehicle routes prior to realization of
demands. Our tes...
Technical Note—Heuristics for Delivery Problems with Constant Error Guarantees
Transportation Science - Tập 24 Số 4 - Trang 294-297 - 1990
In this paper Q Iterated Optimal Tour Partitioning, and Best Optimal Tour
Partitioning algorithms are studied and analyzed for their worst case error.
Both algorithms are based on partitioning an optimal traveling salesman tour in
order to generate a feasible solution to the unit weight delivery problem. They
have a worst case error bound of 2 − 1/Q where Q is the maximal number of
customers a veh...
An Adaptive Dynamic Programming Algorithm for the Heterogeneous Resource Allocation Problem
Transportation Science - Tập 36 Số 2 - Trang 231-249 - 2002
We consider an aggregated version of a large-scale driver scheduling problem,
derived from an application in less-than-truckload trucking, as a dynamic
resource allocation problem. Drivers are aggregated into groups characterized by
an attribute vector which capture the important attributes required to
incorporate the work rules. The problem is very large: over 5,000 drivers and
30,000 loads in a ...
An Adaptive Dynamic Programming Algorithm for Dynamic Fleet Management, II: Multiperiod Travel Times
Transportation Science - Tập 36 Số 1 - Trang 40-54 - 2002
In a companion paper (Godfrey and Powell 2002) we introduced an adaptive dynamic
programming algorithm for stochastic dynamic resource allocation problems, which
arise in the context of logistics and distribution, fleet management, and other
allocation problems. The method depends on estimating separable nonlinear
approximations of value functions, using a dynamic programming framework. That
paper...
Discretization and Validation of the Continuum Approximation Scheme for Terminal System Design
Transportation Science - Tập 40 Số 1 - Trang 89-98 - 2006
This paper proposes an algorithm that automatically translates the “continuum
approximation” (CA) recipes for location problems into discrete designs. It
applies to terminal systems, but can also be used for other logistics problems.
The study also systematically compares the logistics costs predicted by the CA
approach with the actual costs for discrete designs obtained with the automated
procedu...
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