Absence Of Congestion Research Articles

On revenue recycling and the welfare effects of second-best congestion pricing in a monocentric city

This paper examines congestion taxes in a monocentric city with pre-existing labor taxation. When road toll revenue is used to finance labor tax cuts, 35% of the optimal road tax in our numerical model does not reflect marginal external congestion costs, but rather functions as a Ramsey–Mirrlees tax, i.e. an efficiency enhancing mechanism allowing for an indirect spatial differentiation of the labor tax. This adds a quite different motivation to road pricing, since welfare gains can be produced even in absence of congestion. We find that the optimal road tax is non-monotonic across space, reflecting the different impacts of labor supply elasticity and marginal utility of income, which both vary over space. The relative efficiencies of some archetype second-best pricing schemes (cordon toll, flat kilometer tax) are high (84% and 70% respectively). When road toll revenue is recycled lump-sum, the optimal toll lies below its Pigouvian level. Extensions in a bimodal framework show that the optimality of using road toll revenue to subsidize public transport depends on the initial inefficiency in public transport pricing.

Effect of Phased Evacuations in Megaregion Highway Networks

Evacuation phasing or staging is a technique used to disperse traffic so that sudden, wide-ranging surges in travel demand do not overwhelm the available capacity of a road network during an emergency. Despite their many benefits, phased evacuations are not an appropriate strategy for all locations and conditions. Even though researchers have evaluated various aspects of their use, little, if any, systematic study of staged evacuations has been conducted over large multiregional areas. A research effort to simulate staged evacuations in a megaregion addresses this information gap. Megaregions are thought to be particularly vulnerable to evacuation problems because of their enormous populations, wide geographic expanses, and common locations along oceanic coasts or major inland waterways. A range of demand levels was used to investigate the effects of phased evacuation under different scenarios of road network congestion. Because mass evacuations are infrequent and a full megaregion evacuation never has been conducted, this simulation-based framework offered an opportunity to create and assess a megaregion mass evacuation in microlevel detail. Simulation results revealed that the effectiveness of phased evacuations could vary widely according to the level of demand and congestion in the network. In general, no significant improvements could be gained by phasing when the network was only marginally congested or in the absence of congestion. The methods presented can be used for other locations and for other types of hazards, but whether similar levels of effectiveness would be experienced in other locations or for other events is unknown.

Prognostic Value of the Physical Examination in Patients with Heart Failure and Atrial Fibrillation: Insights from the AF-CHF Trial

(Table). Absence of congestion was defined as the absence of jugular venous distension, dyspnea, rales, and pedal or sacral edema on hospital day 7 or discharge. The associations between Loop Dose, discharge congestion status, and all-cause mortality and worsening HF events (HF hospitalization; unscheduled outpatient or emergency department visit associated with IV therapy for HF; or death from HF) within 90 days of randomization were assessed. Results: Median Loop Dose for all subjects was 93 mg and did not differ in 2558 subjects with discharge congestion (89 mg) vs. 600 subjects without discharge congestion (107 mg), p50.36. At 90 days, mortality and worsening HF events occurred in 7.5% and 15.4% of subjects respectively. Higher Loop Dose was associated with clinical markers of more severe disease (Table) and increased risk of mortality (HR 1.37, p!0.001 for one unit increase in natural-log-transformed dose) and worsening HF (HR 1.68/2.35 as compared to Medium/Low Doses, p!0.001). The association between Loop Dose and outcome events did not differ in patients with or without persistent congestion at the time of hospital discharge (for all-cause mortality, with congestion HR 1.44 vs. without congestion HR 0.94, p50.10 for interaction term; and for worsening HF, with congestion HR 1.57 vs. without congestion HR 1.28, p50.18 for interaction term). Conclusion: Higher Loop Dose during hospitalization was associated with worse clinical status, increased short-term all-cause mortality, and increased risk of worsening HF events. The association between in-hospital diuretic dose and clinical outcomes did not differ in patients with or without clinical signs and symptoms of congestion at hospital discharge.

The Emperor has no problem: Is there really Wi-Fi congestion at 2.4 GHz?

“Wi-Fi congestion is a very real and growing problem.” So said then-Chairman of the FCC Genachowski in a recent proceeding, and this sentiment is widely heard. However, we are aware of very few engineering studies that have a bearing on this matter, and their conclusions are equivocal. Beyond this, evidence for “congestion problems” in the 2.4 GHz ISM band is anecdotal at best. While some users no doubt sometimes have service difficulties they ascribe to congestion, that is not sufficient to prove that there is a policy problem. In order to provide a basis for policy decisions, we offer an analysis of congestion metrics and results in the engineering literature. We conclude that there is little consensus on how to measure congestion, and that network metrics are difficult to correlate with user experience. We therefore propose a list of user experience-oriented service impairment criteria that, if met, would demonstrate that congestion exists to a degree that justifies regulatory intervention: For more than one key scenarios that are provided by an operator or technology there is a significant increase in the percentage of users who can’t complete a valuable task on a persistent, ubiquitous basis in spite of the use of state-of-the-art engineering/deployment best practices, and users’ willingness to pay the market rate for the best available service level. Based on our assessment of public reports and experimental data, we conclude that there is currently no evidence for pervasive Wi-Fi congestion. We do not claim that the absence of evidence of congestion amounts to evidence for the absence of congestion. However, we do question the argument that congestion occurring somewhere, sometimes is a justification for regulatory intervention.

Diagnostic Accuracy Under Congestion

In diagnostic services, agents typically need to weigh the benefit of running an additional test and improving the accuracy of diagnosis against the cost of delaying the provision of services to others. Our paper analyzes how to dynamically manage this accuracy/congestion trade-off. To that end, we study an elementary congested system facing an arriving stream of customers. The diagnostic process consists of a search problem in which the service provider conducts a sequence of imperfect tests to determine the customer's type. We find that the agent should continue to perform the diagnosis as long as her current belief that the customer is of a given type falls into an interval that depends on the congestion level as well as the number of performed tests thus far. This search interval should shrink as congestion intensifies and as the number of performed tests increases if additional conditions hold. Our study reveals that, contrary to diagnostic services without congestion, the base rate (i.e., the prior probability of the customer type) has an effect on the agent's search strategy. In particular, the optimal search interval shrinks when customer types are more ambiguous a priori, i.e., as the base rate approaches the value at which the agent is indifferent between types. Finally, because of congestion effects, the agent should sometimes diagnose the customer as being of a given type, even if test results indicate otherwise. All these insights disappear in the absence of congestion. This paper was accepted by Martin Lariviere, operations management.

On Revenue Recycling and the Welfare Effects of Second-Best Congestion Pricing in a Monocentric City

This paper explores the interactions between congestion pricing and a tax-distorted labor market within a monocentric urban equilibrium model. We compute the efficiency gains of various second-best policies, i.e. combinations of toll schemes and revenue recycling programs, with a predetermined level of public revenue. We find that 35% of the space-varying road tax does not reflect marginal external congestion costs, but rather functions as a Ramsey-Mirrlees tax, i.e. an efficiency enhancing mechanism allowing space differentiation of the labor tax. Such a space-varying tax adds a quite different motivation to road pricing, since it can produce large welfare gains even in the absence of congestion. We show that both a cordon toll and a flat kilometer tax achieve over 80% of these gains when combined with specific types of revenue recycling, such as labor tax cuts or public transport subsidies. Sensitivity analysis shows that the optimal type of revenue recycling depends on the level of inefficiency in the provision of public transport prior to the introduction of congestion pricing.

Orchestrating parallel TCP connections: Cyclic and probabilistic polling policies

The standard Transmission Control Protocol (TCP) is based on an additive rate increase in the absence of congestion, and on multiplicative decrease triggered by congestion signals. However, it does not scale well as the distances, or as the speed of the network, increase. Thus, we study some of the solutions that have been proposed to encounter this problem. These solutions include (i) splitting the transmission from a source to its destination into several parallel connections, and (ii) using Scalable TCP, which is a more aggressive version of TCP. The connection whose rate decreases when a signal arrives is chosen either at random or according to a round robin policy. Our analysis concentrates on a centrally controlled TCP system having N connections. We consider both Additive Increase Multiplicative Decrease (AIMD) and Multiplicative Increase Multiplicative Decrease (MIMD) control mechanisms. The Laplace–Stieltjes Transforms (LST) of the transmission rate of each connection at a polling instant, as well as at an arbitrary moment, are derived. Explicit results are obtained for the mean transmission rate and (in contrast to most polling models) for its second moment. For the AIMD procedure under the cyclic visit policy we show that, for both dynamic (Hamiltonian-type) and static visit orders in each cycle, the connections should be visited following a simple index rule in order to achieve maximum throughput. For the probabilistic visit policy we obtain the set of optimal probabilities that maximizes mean throughput. The analysis of the probabilistic MIMD models uses transformations yielding a system’s law of motion equivalent to that of an M/G/1 queue with batch service. The MIMD control mechanism with probabilistic strategy is further analyzed for the case where the transmission rate is bounded above.

Fiscal Policy, Congestion, and Endogenous Growth

AbstractWe devise an endogenous growth model with private and public physical capital, and human capital, which allows for relative and absolute congestion. According to empirical evidence, long‐run growth is invariant to fiscal policy. Despite its complexity, the dynamics of the market economy and the centralized economy are analyzed in detail. We show that an increase in absolute congestion reduces the long‐run growth rate of output. In contrast, relative congestion does not affect long‐run growth. In the absence of congestion, it is optimal to use lump‐sum taxation, and with congestion it is optimal to also tax income.

Haematological and gill responses in parasitized tilapia from valley of Tijucas River, SC, Brazil

In the State of Santa Catarina there is no information about haematological and parasitological characteristics of fish maintained in feefishing operations and manured ponds. This work compared the haematological characteristics of Nile tilapia parasitized or not, captured in a property situated in Nova Trento, SC, Brazil, between August 2003 and July 2004. During the studied period, the water temperature, pH, dissolved oxygen, alkalinity, ammonia and transparency were measured. Ten fish were collected monthly either in a feefishing or in a pond receiving pig manure, and anesthetized with benzocaine solution for haematological, parasitological and histopathological exams. From a total of 360 analyzed fish, 64 (17.8%) were parasitized with Cichlidogyrus sclerosus and Cichlidogyrus sp. (Monogenoidea: Ancyrocephalidae), 20 (5.5%) with Trichodina sp. (Protozoa: Ciliophora), and four (1.1%) with Lamproglena sp. (Crustacea: Lernaeidae). The total number of erythrocytes, thrombocytes and leucocytes, glucose rate and the percentages of hematocrit, lymphocytes, monocytes and neutrophils did not show relation with parasitism. Histopathological analysis showed moderate hyperplasia and absence of congestion. The low level of parasitism found in the animals was not responsible for haematological alterations.

Rate-limited EAFRP-a new improved model for high-speed network traffic

The Extended Alternating Fractal Renewal Process (EAFRP) model has recently been proposed for modeling the self-similar and impulsive traffic of high-speed networks. For mathematical simplicity, it assumes that the available transmission bandwidth in the network is infinite. In reality, the network has a limit R on the total traffic rate through it, and in addition, the ith user's traffic rate is often limited to special value L/sub i/, which is assigned by the bandwidth sharing protocol. We propose a model for single-user traffic, which, by taking into account the aforementioned rate limit L/sub i/ and R, and in the absence of congestion, provides insight on the distinctive two slope behavior of the loglog survival function of multiuser traffic. For small to medium number of users, such as in local area networks (LANs), the model results in non-Gaussian traffic, whereas as the number of users increases, the resulting traffic is Gaussian, both of which are consistent with real network measurements. We discuss model parameter estimation, provide queuing analysis of the multiple-user traffic model, and, based on real data, show that it achieves a closer approximation of the observed reality than existing models.

Dimensioning IP access links carrying data traffic

This paper proposes simple dimensioning rules for high speedip access links carrying data traffic. Assuming a finite source population and fair bandwidth sharing among user flows, we derive formulas relating capacity, demand and performance. These formulas allow link dimensioning for a target quality of service expressed in terms of useful per-flow throughput. They constitute a data traffic model equivalent of the Engset model for telephone access networks. Performance is shown to be largely independent of detailed traffic characteristics such as the statistical distributions of flow size and think time. Simple approximations are derived for two distinct performance regimes corresponding to transparency and saturation, respectively. Extensions to the basic model account for a heterogeneous user demand, unfair bandwidth sharing or different access rate classes. In any case, the key parameter for dimensioning is the offered traffic, defined as the average data rate a user would generate in the absence of congestion.

Reexamining the effect of packet pricing in the wireless internet

In this paper, we compare the market performances of circuit pricing whereby users are charged based on their length of usage time with packet pricing whereby users are charged based on the amount of information received. We show that, if packet pricing is introduced, the market price rises contrary to a widely held belief, but that the overall social welfare is unambiguously increased. Also, we show that a move to packet pricing lowers the price of multimedia transmission which requires a much higher speed, thereby increasing the usage of multimedia data in the absence of congestion, although this may not be the case in the presence of congestion.

Modeling schedule recovery processes in transit operations for bus arrival time prediction

AbstractMany existing algorithms for bus arrival time prediction assume that buses travel at free‐flow speed in the absence of congestion. As a result, delay incurred at one stop would propagate to downstream stops at the same magnitude. In reality, skilled bus operators often constantly adjust their speeds to keep their bus on schedule. This paper formulates a Markov chain model for bus arrival time prediction that explicitly captures the behavior of bus operators in actively pursuing schedule recovery. The model exhibits some desirable properties in capturing the schedule recovery process. It guarantees provision of the schedule information if the probability of recovering from the current schedule deviation is sufficiently high. The proposed model can be embedded into a transit arrival time estimation model for transit information systems that use both real‐time and schedule information. It also has the potential to be used as a decision support tool to determine when dynamic or static information should be used.

Commuting, congestion, and employment dispersal in cities with mixed land use

For centuries, cities have been modeled as having centered employment—scarce access to which generates land rent. This paper first presents some new empirical evidence that in US cities actual employment turns out to be almost as dispersed as residences. This range of urban forms is generated with analytic ease in a model that assumes land can have “mixed” rather than exclusive use at any location. The model has firms trading off a central-agglomeration force against the lower wages that accompany shorter commuting distances in peripheral locations. At one extreme, with very high agglomerative forces, employment is approximately centered, with long commute distances and high congestion levels. At the other extreme, lower agglomerative forces lead to employment that is completely dispersed, commute distances of zero and the absence of congestion. Maximizing output-minus-congestion never leads to a pattern of land mixing where employment is fully dispersed. A market model, however, often does if the mix at each location is based on the relative magnitude of the land rent offered from residential as opposed to commercial uses.

Optimal network topologies for local search with congestion.

The problem of searchability in decentralized complex networks is of great importance in computer science, economy, and sociology. We present a formalism that is able to cope simultaneously with the problem of search and the congestion effects that arise when parallel searches are performed, and we obtain expressions for the average search cost both in the presence and the absence of congestion. This formalism is used to obtain optimal network structures for a system using a local search algorithm. It is found that only two classes of networks can be optimal: starlike configurations, when the number of parallel searches is small, and homogeneous-isotropic configurations, when it is large.

Influence of peak spreading and departure time choice on evaluation of its measures

AbstractIntelligent transport systems provide various means to improve capacity and travel time in road networks. Evaluation of the benefits of these improvements requires consideration of travellers' response to them. We consider a continuous‐time equilibrium model of departure time choice and identify a formula for the dynamic equilibrium departure rate profile. We develop the analysis to consider the effect on the cost incurred by travellers of ITS measures through their effects on each of the travel time in the absence of congestion, and the capacity for travel. This shows the importance in choice of departure time of travellers' values of time at each of the origin and destination of their journeys. We show the importance of these values of time in evaluation, and that if travellers value their time at both the origin and destination of their journeys, their responses will lead them to achieve a greater reduction in costs than would be achieved under free‐flow conditions.

Time, Self-Selection and User Charges for Public Goods

Many public goods generate utility only when combined with a time-input. Important examples include road networks and publicly provided leisure facilities. If it is possible to charge for the time spent using the public good it is generally a second-best Pareto optimal policy to do so even in the absence of congestion. An optimal linear user charge is analysed within a standard optimum income-tax framework. Second-best public good provision in the presence of a user charge is also characterized and factors that influence the direction of optimal distortion of the public good supply are identified.

Congestion pricing. Paying your way in communication networks

Network congestion is a fundamental problem facing Internet users today. A network where users are selfish, and thus reluctant to defer to other users, may result in the famous "tragedy of the commons", where, in the absence of controls, a shared resource is overconsumed by individuals who consider only their personal costs and not the cost to society as a whole. In terms of the Internet, the "tragedy" could be viewed as congestive collapse, resulting from overconsumption of the shared network resource. It is important to distinguish congestion pricing from other forms of network pricing. Charging network users for the congestion they cause can lead to more efficient network utilization by forcing them to take social costs into account. In a congestion-pricing framework, the congestion charge would replace usage and QoS charges. Users would pay their ISPs a subscription charge to cover fixed costs and a congestion charge only when appropriate. This pricing scheme is feasible because, in the absence of congestion, the marginal cost of a network link is practically zero. Congestion pricing can also benefit network operators. By indicating the level of congestion and the user tolerance of it in their networks, congestion pricing can inform operators about when to re-provision and increase network capacity.

Frange rurali e crescita urbana : la resistenza all'urbanizzazione nel periurbano di Cagliari (Sardegna)

Resistance to suburbanization by a rural community in the metropolitan area of Cagliari, Parteolla, is described. Here the population refused the installation of council houses fearing that the presence of extraneous families of a low social level might worsen the standard of living in the village. In fact, the presence of an agricultural residue, of food producing industries (cheese factories, oil mills, wineries) and even the arrival of shepherds families from inland contribute to maintaining alive the rural element, and with this some environmental values such as the traditional landscape and the absence of congestion.

Spatial variation of the marginal utility of income and unequal treatment of equals

In one of the most famous contributions to the “new” urban economics literature, Mirrlees [6] showed that a utilitarian planner, able to control the distribution of income (or endowments) across households, the consumption of land (or housing), and the distribution of population over space, would treat households with identical tastes unequally in the sense that utility levels would vary among them at the planner’s optimum. Similar results were obtained by Dixit [2], who showed that even more inequality-averse social welfare functions than the utilitarian one would result in unequal treatment. He concluded that only the Rawlsian maximin welfare function would produce the equal treatment outcome.2 This result has generated considerable attention (see, e.g., Mills and Mackinnon [5]) because of its apparently paradoxical nature. The purpose of this note is to present a new way of thinking about, and making plausible, the unequal-treatment result.3 To develop the intuition, recall that in monocentric city models where equals are treated equally, that is, where households have equal endowments, a market equilibrium with free mobility is characterized by equal utilities for all (assuming identical preferences). As is well known, in the absence of congestion or other market failures, this market equilibrium is Pareto-efficient, producing the maximum feasible common level of utility. Imagine now a Mirrlees planner, coming across such an equal-utility equilibrium. Under what conditions would the planner not want to disturb the market equilibrium? Clearly, a necessary condition for equal treatment to be utilitarian-optimal is that the marginal utility of income be the same for all households in the market equilibrium. Otherwise, freezing the allocation of resources in every other respect, social