Search

Modifications are proposed for an algorithm that estimates the number of vehicles on a section of highway from a time series of flow and velocity measurements. The effect of alternate assumptions concerning the nature of the velocity field between points of measurement is explored. In addition a simplification is proposed to avoid solution by Successive approximation of certain transcendental equations. The net result is an algorithm that is more practical and provides generally superior performance than the original. Various algorithms are evaluated for both single and multilane traffic. [ABSTRACT FROM AUTHOR]

Exogeneous events occurring as a Poisson process are assumed to cause stoppages in the normal operation of convoys, road vehicles, or equipments. The operational delay experienced by each stoppage is assumed to have an exponential distribution. By introducing appropriate state variables, a hyperbolic partial differential equation is set up; expressions are obtained for the probability that at a given time the operation has registered at most a given number of cumulative performance units (e.g., distance) and for the probability that the operation has registered a given number of cumulative performance units on or before a specified time. [ABSTRACT FROM AUTHOR]

A model is developed to determine travel times between points in an urban area with a limited amount of input. The model uses a network consisting of grid shaped links and high speed, freeway links. The travel time over the grid shaped links is computed internally using a macroscopic description of travel velocities and paths. A minimum time algorithm is applied to the network to find the minimum travel times between all points in the network. A test of the procedure showed that the results of the grid travel time model closely agreed with travel times produced by the standard detailed network method. The grid model uses substantially less input and performs its computations in a very short period of time. It is possible to develop a model that closely agrees with the detailed network model with even greater simplification. The procedure developed seems to have promise for a number of applications in the transportation planning process. [ABSTRACT FROM AUTHOR]

The problem of determining a schedule for a traffic system of, e.g., bus or air lines that uses a minimum number of vehicles is treated. The various trips are required to start within given time intervals and have given origins, destinations, and travel times. It is shown that the problem can be formulated as an integer LP problem, but not of the simple network flow type. A rather simple branch-and-bound procedure is devised for its solution, which has been tested with favorable results. [ABSTRACT FROM AUTHOR]

Since the speed of travel on a road usually decreases as flow increases, there are often advantages in extending the period over which travelers on a road system begin their journeys, but, since travelers often wish to reach their destinations almost simultaneously, there are also advantages in reducing the period over which they spread their journeys. This suggests that there may be an optimum period during which vehicles should begin their journeys on a road system in order to reach their destinations within the shortest possible time. An analysis of the situation suggests that, if n vehicles spread their entry times into a road system uniformly over a period of time t and travel an average distance l, then the time from the first vehicle entering to the last vehicle arriving at its destination is a minimum when (1/v²)(dv/dq) + (t²/nl) = 0, where v is the average speed when the flow is q vehicles per unit time. The average journey time (also measured from the entry time of the first vehicle is minimal when (1/v²) (dv/dq) + (t²/2nl) = 0. These considerations have been applied to the case of vehicles entering a city center during peak travel periods. The calculations suggest that the 'optimum' duration of entry times is associated with a particular average speed of travel, which is itself dependent on the value of fA/n, where f is the fraction of the surface area A of the city center used for roads. [ABSTRACT FROM AUTHOR]

Vehicles load passengers at a single service point and, after traversing some route, return for another trip. The travel times of successive trips are independent identically distributed random variables with a known distribution function. After a vehicle returns to the service point, one has the option of holding it, or dispatching it immediately. Passengers arrive at a uniform rate and the objective is to minimize the average wait per passenger. The problem of determining the optimal strategy (dispatch or hold) for a system of m vehicles is formulated as a dynamic programming problem. It is analyzed in detail for m = 1 and m = 2. For m = 1, the optimal strategy will hold a vehicle if it returns within less than about half the mean trip time. For m = 2, and for a small coefficient of variation of trip time C( T), the optimal strategy will control the vehicles so as to retain nearly equally spaced dispatch times, within a range of time proportional to C4/3(T). [ABSTRACT FROM AUTHOR]

Travel-time connectivity is a key factor in defining a process of the spatial reorganization of man's functional establishments. A case study relating highway development with the growth in wholesale activity for selected cities in the upper midwest of the United States indicates that, aside from being a good surrogate of transport efficiency, travel-time connectivity is also a good measure of the relative advantage of a given place in attracting to itself the centralization and specialization of human activity. [ABSTRACT FROM AUTHOR]

This article deals with the problem of traffic assignment with a nonlinear travel-time function. The nonlinear travel-time function makes it possible to simulate congestion on urban streets. The optimal traffic assignment pattern is obtained by using a variational technique for a multicopy network problem with nonlinear travel-time functions and turn penalties. The distinguishing characteristic of this type of assignment using nonlinear travel-time-volume relations, is that as the number of vehicles on any path tends to increase, alternate paths tend to become more desirable and thus utilized by other vehicles.

Two transportation systems, following the same alignment, serve an area from which population commutes to a central point. One system has a constant speed and can be taken at any point along the line; the other has a discrete movement and can be boarded at stations only. The study analyzes the optimal station locations of the latter system for which its patronage will be maximum, assuming that passengers select systems on the basis of shorter travel time. The optimal solution, derived analytically and shown graphically on a time-distance diagram, indicates that the interstation spacings for this objective should be increasing at a decreasing rate in the direction of cumulation. Compared with the optimal interstation spacings for minimum total passenger travel time, given in a recent paper by VUCHIC AND NEWELL, this solution has a greater density of stations and, naturally, larger travel times. Sensitivity of the two solutions to various parameters is examined. Several problems to which this model would be applicable are shown and the model's realistic validity is discussed. From the optimal solution and numerical examples, several conclusions are drawn that are directly relevant to the planning of station locations for discrete public transportation systems. [ABSTRACT FROM AUTHOR]