Since the progressive era, American cities have generally expanded their authority in policymaking and service provision. State governments have at times acted to preempt city authority on particular points of policy, but it is unclear whether the threat of this action inspires caution in the decision making of city leaders. The results of an experimental survey distributed to elected city officials across the United States show that a perceived threat of preemption does not significantly discourage city leaders in supporting a proposed broadband internet service provision. These results suggest that political pressure in the form of preemption is not persuasive to city leaders, and that local representational interests are likely more influential on municipal government.

In MPLS networks, CR-LDP (Constraint-Based Routed Label Distribution Protocol) provides traffic engineering and QoS (Quality of Service) by distributing labels along the path. One of the innovative ideas in CR-LDP is right in the capability of bandwidth preemption. Bandwidth preemption allows a high-priority traffic flow to pre-empt the low-priority traffic flow when there is not enough bandwidth for conveying the high-priority flow. However, it is not effective in assuring QoS by simply pre-empting the low-priority flow. Therefore, in the thesis, we present a bandwidth preemption with negotiation (BPN) architecture for MPLS networks. In BPN, a high-priority flow will have to negotiate the bandwidth with Ingress Switch Router (ISR) before it can actually pre-empt the bandwidth being used by the low-priority flow. A network link-state database in ISR is designed to record the remaining bandwidth for each priority class. ISR determines whether a high-priority flow can pre-empt a low-priority flow based on the condition that the low-priority flow is possible to switch to other paths with an equal bandwidth along the path. In order to evaluate the performance of our proposed BPN mechanisms, we modify the MNS (MPLS Network Simulator) by adding a bandwidth negotiation module. For the comparisons, we design two topologies for simulating the proposed BPN and the traditional bandwidth preemption with force mode. It is observed that the BPN have exhibited better performance in average throughput and packet loss rate than the traditional bandwidth preemption, not matter either a complex or a regular topology is used. Finally, we analyze the BPN algorithm complexity by some network parameters, and compare the complexity with that of traditional bandwidth preemption

Because the operational characteristics of signalized intersections near highway-railroad grade crossings (IHRGCs) are different from those of signalized intersections located elsewhere in the traffic system, standard operational strategies do not apply. This is because safe operation at IHRGCs takes precedence over all other objectives. Because the prime objective of the current preemption methods is to clear the crossing, secondary objectives such as safe pedestrian crossing time and minimized delay are given less consideration or ignored completely. Consequently, state-of-the-practice strategies may cause serious pedestrian safety and efficiency problems at IHRGCs. Therefore, there is a definite need for research on how to improve traffic signal preemption strategies. An important element of preemption strategy is detection of trains and prediction of arrival times. However, because of the limitations of current detection technologies, estimation algorithms, etc., there is a wide range in these warning times. In this dissertation, a new train-arrival prediction algorithm was developed using detection equipment located farther upstream from the HRGC. The state-of-the-art transition preemption strategy (TPS) was developed to ensure that as preemption is initiated by approaching trains, the signal display does not change in a manner that endangers either pedestrians or drivers. However, because it does not account for the variability of predicted train arrival times, there is still a possibility of failure. Therefore, a new transition preemption algorithm that is specifically designed to improve intersection performance while maintaining or improving the current level of safety is developed. This dissertation developed a preemption strategy (TPS3) that uses better train arrival time estimates to improve the safety and efficiency of IHRGCs. The approach was simulated on a test bed in College Station, Texas, and it was concluded that the new TPS improves the safety and operation of intersections near highway-railroad grade crossings.

Aravind Chandrashekar, for the Master of Science degree in Electrical and Computer, presented on 02/09/2011, at Southern Illinois University Carbondale. TITLE: Reduction of Cache Related Preemption Delay using DVS in Real Time Systems MAJOR PROFESSOR: Dr. Harini Ramaprasad Embedded/real-time systems are ubiquitous in today's world. Providing temporal guarantees is paramount in such systems. In several multi-tasking real-time systems, tasks are assigned varying priorities and scheduled in accordance with a preemptive scheduling policy. When a task is preempted, a significant number of memory blocks belonging to the particular task are displaced from the cache memory between the time that the task is preempted and the time that the task resumes execution. Upon resumption, a corresponding amount of time is spent in reloading the cache with previously replaced memory blocks, thereby incurring what is known as cache-related preemption delay (CRPD). CRPD of a task due to a given preemption depends on the position in the program where the preempted task is executing at the time of preemption. As such, CRPD at different preemption points may be significantly different. In this thesis, we exploit this difference in CRPD and use dynamic voltage/frequency scaling (DVFS) to control the execution speed of a task such that it gets preempted in regions where the CRPD is low, as far as is possible without jeopardizing system schedulability. Simulation results demonstrate that our algorithm reduces number of cache reloads due to preemption to a reasonable extent, thereby reducing the repeated usage of off-chip memory bandwidth.

Lewis's counterfactual analysis of causation starts with the claim that c causes e if ~ C > ~ E, where c and e are events, C and E are the propositions that c and e respectively occur, ~ is negation and > is the counterfactual conditional. The purpose of my project is to provide a counterfactual analysis of causation which departs signigicantly from Lewis's starting point, and thus can hope to solve several stubborn problems for that approach. Whereas Lewis starts with a sufficiency claim, my analysis claims that a certain counterfactual is necessary for causation. I say that, if c causes e, then ~ E > ~ C - I call the latter the Reverse Counterfactual. This will often, perhaps always, be a backtracking counterfactual, so two chapters are devoted to defending a conception of counterfactuals which allows backtracking. Thus prepared, I argue that the Reverse Counterfactual is true of causes, but not of mere conditions for an effect. This provides a neat analysis of the principles governing causal selection, which is extended in a discussion of causal transitivity. Standard counterfactual accounts suffer counterexamples from preemption, but I argue that the Reverse Counterfactual has resources to deal neatly with those too. Finally I argue that the Reverse counterfactual, as a necessary condition oncausation, is the most we can hope for: in principle, there can be no counterfactual sufficient condition for causation.

This research analyzed and evaluated a new strategy for preemption of emergency vehicles along a corridor, which is route-based and adaptive to real-time traffic conditions. The method uses dynamic offsets which are adjusted using congestion levels to provide uninterrupted preempted green signal for the emergency vehicle throughout its route. By achieving a higher average emergency vehicle speed, this method promises faster emergency response which results in saving life and property as well as larger emergency service radius for the dispatch stations. The research evaluated the effectiveness of two possible algorithms for offset adjustment using measured vehicle queues. It is showed to reduce the emergency vehicle travel-time by 31 percent when compared to cases without preemption and 13 percent when compared to traditional method of individual-intersection preemption. / Master of Science

Highway traffic control systems have been deployed to provide emergency vehicle preemption (EVP) at signalized intersections. Industry and transportation researchers have worked to develop analytical methods to establish the degree of benefit of emergency vehicle preemption to the emergency vehicle (EV) community and the impact on other road user groups. This thesis report illustrates the use of an analytical method to evaluate the potential impacts of EVP related to EV safety, and the potential delay to EVs and vehicles on the side street. The method uses EV-specific conflict point and delay analysis with video and other data collected in a field study conducted in Northern Virginia at the intersection of Southgate Drive and U.S. 1. EV related conflict points are characterized in terms of the EV/auto interaction geometry, the signal display, and the severity of potential crashes. EV related delay is characterized in terms of the EV/auto interaction geometry, the signal display, the level of service and the amount of delay to the EV. The EV/auto interaction, the queue length and the signal display characterize increase in delay to vehicles on the side street. The analysis indicates that the severity of EV-specific conflict points is significantly reduced with EVP. The delay to EV does not change significantly and the delay to the vehicles on the side street auto traffic increases. / Master of Science

Concerns about increased emergency vehicle response times in the Washington D.C. Region, especially during peak periods, have led to the implementation of signal preemption systems to facilitate the efficient and safe movement of emergency vehicles. However, to date only limited research has been carried out on the travel characteristics of emergency vehicles. This paper presents an analysis of emergency vehicle characteristics to enhance our understanding of emergency vehicle operations and impacts and to assist public agencies and other stakeholders in the planning and deployment of emergency vehicle preemption systems. Emergency vehicle characteristics that merit special attention include temporal and spatial distribution of emergency vehicle travel; frequency and duration of preemption requests; platoon responses; and crashes involving emergency vehicles. Data on major corridors in Fairfax County, Virginia and Montgomery County, Maryland are used in the analysis. The analysis indicates that such data are useful to assess the need for a preemption system along major arterials. Moreover, the analysis demonstrates the importance of considering emergency vehicle preemption impacts regarding delay to other vehicles. It is also important to note that there is some variability in the emergency vehicle characteristics depending on the proximity of a firehouse to an intersection and other factors. It is proposed that future efforts build upon this research to develop warrants to be used in determining the appropriateness of installing preemption systems at signalized intersections. / Master of Science

Access to highways from a local firehouse is a major problem for emergency services. Motorists often do not see flashing lights or hear sirens from the approaching emergency vehicles (EV) until emergency vehicles reach the highway entrance, often too late to take appropriate action. Many locations have installed special signals called emergency traffic signal systems (ETSS) or used signal preemption to notify motorists and to stop traffic to allow the emergency vehicle to enter the highway safely. This thesis will examine the effectiveness of one such installation at the intersection along U.S.1 at Beedo Street and some of the impacts it has on highway traffic. The evaluation of the said installation is carried out in terms of delay to EV; conflict potential between EV and other vehicles and response of the motorists to the ETSS. This thesis also proposes two alternative designs of ETSS to improve the existing signal system. / Master of Science

This dissertation will examine the dangers created by governmental entities that possess or seek to possess weapons of mass destruction (WMDs), for possible use against other states. In order to counter such a threat, traditional notions of anticipatory self-defense such as preemption might prove ineffective as the deployment of WMDs can be carried out in a matter of minutes. As a result of this, some jurists and politicians have called for the broadening of anticipatory self-defense to include preventive force. While the use of preemptive force has been recognized as a legitimate form of selfdefense, such recognition has not been extended to the use of preventive force. This research attempts to answer the following questions: Under what circumstances can preventive force be used against a target state that develops WMDs with the alleged intention to use them? And what procedures would ensure that preventive force is used in a manner that minimizes the possibility of abuse by the state claiming to exercise its right of self-defense? The dissertation will propose a normative framework that will define the scope of the lawful use of preventive force when a state is claiming to be using such force against another state as an exercise of self-defense. The proposed legal framework takes into consideration both recent legal developments as well as relevant instances of state practice in order to circumscribe the use of preventive force to clearly defined cases. The determination of the legality of a preventive strike should be made by the United Nations Security Council. The Security Council would be presented with a proposed preventive strike by a state making the allegation that the strike is necessary to stop another state from developing WMDs that would be used against it in the future. In order to secure an approval for the preventive strike, the “preventor” state would have to show compelling reasons, such as the target state’s prior bad actions, as to why such a strike is necessary. / acase@tulane.edu