Delay Savings Research Articles

Selective shielding technique to eliminate crosstalk transitions

With CMOS process technology scaling to deep submicron level, propagation delay across long on-chip buses is becoming one of the main performance limiting factors in high-performance designs. Propagation delay is very significant when adjacent wires are transitioning in opposite direction as compared to transitioning in the same direction. As opposite transitions on adjacent wires (called as crosstalk transitions ) have significant impact on propagation delay, several bus encoding techniques have been proposed in literature to eliminate such transitions. We propose selective shielding technique to eliminate crosstalk transitions. We show that the selective shielding technique requires ⌈3 n /2⌉ wires to encode a n -bit bus. SPICE simulations by considering 90nm technology nodes reveal that, for uniformly distributed random data, our technique achieves nearly 39% (21%) delay savings over 10 mm -length uncoded 32-bit bus for pipelined (nonpipelined) data transmission at the cost of nearly 7% energy overhead.

FinFET domino logic with independent gate keepers

Scaling of single-gate MOSFET faces great challenges in the nanometer regime due to the severe short-channel effects that cause an exponential increase in the sub-threshold and gate-oxide leakage currents. Double-gate FinFET technology mitigates these limitations by the excellent control over a thin silicon body by two electrically coupled gates. In this paper a variable threshold voltage keeper circuit technique using independent-gate FinFET technology is proposed for simultaneous power reduction and speed enhancement in domino logic circuits. The threshold voltage of a keeper transistor is dynamically modified during circuit operation to reduce contention current without sacrificing noise immunity. The optimum independent-gate keeper gate bias conditions are identified for achieving maximum savings in delay and power while maintaining identical noise immunity as compared to the standard tied-gate FinFET domino circuits. With the variable threshold voltage double-gate keeper circuit technique the evaluation speed is enhanced by up to 49% and the power consumption is reduced by up to 46% as compared to the standard domino logic circuits designed for similar noise margin in a 32nm FinFET technology.

Value of Flight Cancellation and Cancellation Decision Modeling

Flight cancellations are costly to airlines and air passengers, but the question is, how costly? Little quantitative analysis about cancellation cost has been done, and current studies are focused on flight delays. However, cancellations should be studied to supplement delay metrics to assess the performance of the National Airspace System, as well as to evaluate the effectiveness of air traffic management. Postoperation data of the ground delay program were explored, and relative value of cancellations in terms of delay savings were inferred. Two cancellation metrics were developed for this purpose. In addition, flight cancellation decisions were modeled with a discrete choice model by using the two cancellation metrics that were generated as well as some other flight characteristics. Three models are presented in this study. The results reveal the value of a flight cancellation and airline preference structure in making decisions in canceling a flight in response to schedule disturbance. The study contributes to the literature in a distinct way: post-operation data are used to understand airline flight cancellation behavior in the context of ground delay programs.

A modelling technique for assessing linked MOVA

This paper introduces an innovative approach to evaluating the benefits of linked MOVA (Microprocessor Optimised Vehicle Actuation) using a micro-simulation modelling and programming technique. The implementation of linked MOVA at signal-controlled junctions has been found to provide more efficient junction operations by either maximising capacity or minimising delay, depending on the level of congestion. Although vehicle actuation (VA) modelling is commonly available (i.e. bus gating, standalone MOVA and SCOOT), there has been no method for assessing the operational benefits and signal settings of linked MOVA implementation. Using the programming ability within the VISSIM micro-simulation software suite, a precise assessment of the benefits of linked MOVA type VA was undertaken. The signal settings, operational parameters and ‘linking’ of the signal control junctions were set as part of the MOVA implementation in evaluating the operational benefits. A post-implementation evaluation study is presented in which modelled operations replicated the actual operations in line with modelling standards. The model is calibrated and validated using post-MOVA implementation surveys. The results proved a significant operational benefit. On average, delay savings of 19·7% were achieved by the implementation, together with a significant reduction in total stopped delay and number of stops. Although traffic demand remained constant for pre- and post-linked MOVA operations, a 0·5% increase in throughput was observed. Modelling proved an effective method in assessing linked MOVA operations. This technique is now available to linked MOVA users, and can be adapted to other VA-type signal operations in evaluating the coordinated operations, benefits and settings before expensive implementation is undertaken.

Evaluating Benefits of Systemwide Adaptive Ramp-Metering Strategy in Portland, Oregon

A systemwide adaptive ramp-metering (SWARM) system is being implemented in the Portland, Oregon, metropolitan area, replacing the previous pretimed ramp-metering system. SWARM has been deployed on six major corridors and operates during the morning and afternoon peak hours. This study entails a before and after evaluation of the benefit of the new SWARM system as compared with the pretimed system using the existing data, surveillance, and communications infrastructure. In particular, the objective of this study is to quantify the systemwide benefits in relation to savings in delay, emissions and fuel consumption, and safety improvements on and off the freeway due to the implementation of the SWARM system. A pilot study was conducted for 2 weeks on a 7-mi freeway corridor in an attempt to develop a strategic design for the future regional-level study. This paper discusses the selection process of the study corridor, the experimental design, and the results obtained from the pilot study.

Active Signal Priority for Light Rail Transit at Grade Crossings

The basic concept and implementation of an active priority system of light rail transit (LRT) for highway–rail grade crossings are presented. The proposed priority system consists of four major components: train detectors, train travel and dwell time predictors, priority request generator (PRG), and traffic signal controllers. As the brain of the system, the PRG adopts a three-scheme conditional priority control strategy. Scheme I, which applies to late LRT trains, features a timing optimization model. The objective of this optimization model is to minimize intersection delays for late trains and meanwhile to minimize impacts on other traffic. Unlike existing signal priority studies, which typically focus on isolated intersections, the proposed model deals with signal timings at multiple intersections and provides an optimized green band for an incoming train. The optimized green band would start at the right time to cover the predicted train arrival time and would be wide enough to accommodate prediction errors. A case study, based on the San Diego Trolley system, in California, demonstrates enormous intersection delay savings of 89.5% and 25.3 s/train for late trains after application of the proposed Scheme I strategy. At the same time, the impact on other traffic in the priority cycle is only 4.1 s/veh. For Schemes II and III when no priority is needed, traffic delay savings are 32.5% and 52.0%, respectively. A simulation study confirms the system benefits and validates the practicality of the active priority system for future field testing.

Decision Support System for Predicting Benefits of Left-Turn Lanes at Unsignalized Intersections

Accommodating left turns at unsignalized intersections is one of the most challenging problems in traffic engineering. Over the past 40 years, a few studies developed guidelines to help traffic engineers in deciding when a left-turn lane was warranted for a given situation. Building on these previous attempts, the current study develops a refined decision support system (DSS) for assessing the likely benefits of left-turn lane installations as an aid in deciding whether a left-turn lane is warranted. The developed DSS is designed to predict these likely benefits on the basis of several measures, including delay savings, reductions in percentage of stops, increases in fuel efficiency, and reductions in emissions. The first step in development of the DSS was the use of microscopic simulation to model several real-world unsignalized intersections with different geometric configurations located in different area types. After careful calibration of these models, several scenarios covering a wide range of operational conditions were simulated. The output from these simulation runs was used to train a set of multilayer perceptron neural networks (NNs) and to generalize the results from the models' runs. The NNs were then incorporated into a DSS that can help an analyst quantify the impacts of a proposed new development as well as estimate the benefits of installations of left-turn lanes. The paper concludes by summarizing some conclusions derived from the study.

Managing the power resources of sensor networks with performance considerations

A power management algorithm that schedules the time off intervals for nodes in sensor networks while maintaining network connectivity is proposed. The scheduling problem is formally formulated as a combinatorial optimization problem and is shown to be intractable. The performance of the proposed algorithm is compared to an optimum integer linear programming formulation. It is shown that its performance is very close to the optimum solutions for small instances. The experimental results also show that the proposed heuristic performs better than the ASAP and the sleep and listen component of the S-MAC protocol in terms of delay, throughput and energy savings.

Evaluation of the effectiveness of single-lane two-way traffic control at maintenance and reconstruction zones

This paper presents a study on evaluating traffic control at single-lane closures on two-lane two-way highways. Four traffic control strategies were investigated by this study. Those strategies involved fixed-time control, fixed-queue control, "static optimum" or convoy rule, and adaptive control. Traffic control strategies were modeled using two approaches; a deterministic approach in spreadsheet application and a stochastic approach in microscopic traffic simulation. Parametric analyses were performed using several variables that are related to traffic control at this type of lane closure. Those variables involved work zone length, average speed at work zone, lost time, traffic level, directional split, and interruptions to traffic by movement of construction vehicle and (or) equipment into and out of the construction site. Study results suggest that significant savings in average delay can be accrued by using more advanced traffic control strategies. Those savings could be as high as 53% for the range of conditions investigated by this research.Key words: work zone, flaggers, adaptive control, simulation, optimization.

ON THE DESIGN OF EFFICIENT MODULAR ADDERS

Modular adders are met in various applications of computer systems. In this paper, we investigate a new architecture for their design that utilizes a carry save adder stage and two binary adders that operate in parallel. Realizations in static CMOS reveal that the introduced architecture leads to modular adder implementations that offer significant savings in delay and power consumption over implementations based on previously proposed architectures. In parallel, the proposed architecture offers significantly smaller implementation area for small operand widths.

Design and Operational Performance of Crossover Displaced Left-Turn Intersections

Although the concepts of the crossover displaced left-turn (XDL) intersection (also called the continuous flow intersection) were developed approximately four decades ago, there is no simplified procedure to evaluate its traffic performance and to compare this intersection with conventional intersections. Several studies have shown the qualitative and quantitative benefits of the XDL intersection without providing accessible tools for traffic engineers and planners to estimate average control delays and queues. Modeling was conducted on typical geometries over a wide distribution of traffic flow conditions for three different design configurations or cases using VISSIM simulations with pretimed signal settings. Some comparisons with similar conventional designs showed considerable savings in average control delay, as well as average queue length and increase in intersection capacity. The statistical models provided an accessible tool for the practitioner to assess average delay and average queue length for three types of XDL intersections. Finally, a preferred signal setting was developed for each of the five intersections of the XDL network.

Freeway On-Ramp Metering, Delay Savings, and Diverge Bottleneck

An effort was made to clarify certain issues concerning freeway onramp metering and its potential for saving commuter delay. Simple analogies were used toshow that delay is reduced if ramp metering increases the rates at which commuters exit the freeway. Contrary to what is frequently reported in the literature, higher travel speeds and flows on links within a freeway system are not evidence of diminished delay and this too was made clear by the analogies. The discussion explains why a metering scheme should be specially tailored to the freeway it serves, and why no single metering logic will suffice for all situations. This idea was emphasized by demonstrating that some of the best known on-ramp metering algorithms can actually reduce freeway outflows (and therefore increase delay) when the freeway is plagued by a diverge bottleneck with a congested off-ramp. Other more effective strategies for dealing with the (commonly occurring) diverge bottleneck are described, as are methods of field-testing these strategies. Changes in commuter travel behavior brought by metering, and possible effects of these changes, are discussed as well.

High-occupancy/toll lanes: where should they be implemented?

Since the first high-occupancy toll (HOT) lane was implemented in Orange County, California in 1995 there has been an increasing interest in such lanes as a means to reduce congestion, increase utilization of underutilized high-occupancy vehicle (HOV) lanes, and generate revenue. In order to determine where such lanes are appropriate, a model is constructed to estimate how adding an HOV lane, an HOT lane or a mixed flow lane to an existing freeway affects delay in various circumstances. Except when the initial delay is very high, adding a mixed flow lane is more effective in reducing delay than adding either an HOV or HOT lane, and it costs less. If both the initial delay and the initial proportion of HOVs are very high, then adding an HOV lane is more effective in reducing delay than adding either a mixed flow or HOT lane. But if the initial delay is high and the initial proportion of HOVs is not high an HOT lane is the most effective in reducing delay. Adding an HOT lane should also be considered if substantial growth in traffic is expected, because HOT lanes perform relatively well in terms of reducing delay across all levels of initial delay and HOV usage. However, because HOT lanes are considerably more costly to construct and operate than mixed flow or HOV lanes, the revenue generating potential must also be assessed, and the savings in delay must be sufficient to justify the additional cost. The revenue generating capacity of HOT lanes is low when the initial delay is low, and in such cases alternate methods of utilizing the HOT lane initially might be desirable.

Repeater insertion in tree structured inductive interconnect

The effects of inductance on repeater insertion in RLC trees is the focus of this paper. An algorithm is introduced to insert and size repeaters within an RLC tree to optimize a variety of possible cost functions such as minimizing the maximum path delay, the skew between branches, or a combination of area, power, and delay. The algorithm has a complexity proportional to the square of the number of possible repeater positions and determines a repeater solution that is close to the global minimum. The repeater insertion algorithm is used to insert repeaters within several copper-based interconnect trees to minimize the maximum path delay based on both an RC model and an RLC model. The two buffering solutions are compared using the AS/X dynamic circuit simulator. It is shown that as inductance effects increase, the area and power consumed by the inserted repeaters to minimize the path delays of an RLC tree decreases. By including inductance in the repeater insertion methodology, the interconnect is modeled more accurately as compared to an RC model, permitting average savings in area, power, and delay of 40.8%, 15.6%, and 6.7%, respectively, for a variety of copper-based interconnect trees from a 0.25 /spl mu/m CMOS technology. The average savings in area, power, and delay increases to 62.2%, 57.2%, and 9.4%, respectively, when using five times faster devices with the same interconnect trees.

Benefits of Split Intersections

As urban and suburban intersections become more congested, a likely remedy for recurring traffic jams is grade separation in the form of diamond or tight diamond interchanges. A more economical intersection configuration to relieve congestion has been built overseas. The major highway is separated into two-directional, one-way roads comparable to an at-grade diamond junction known as the split intersection. The split intersection facilitates smoother flows with less driver delay, mainly by reducing the number of required signal phases from four to three. The success of converting to the split intersection has been analyzed by using deterministic methods that showed increased capacity and noticeable reduction in delay. The analysis methodology relies on a microsimulation technique to predicate previous claims and provide economic benefits. Comparisons of vehicular delay between the single and the split intersection revealed substantial savings in travel delay, particularly for higher entering volumes and higher left-turning movements. The findings provide guidance to planners and designers on the expected benefits of converting a four-lane by four-lane single intersection to the split intersection.

Cost-Effectiveness Evaluation of Hoosier Helper Freeway Service Patrol

Hoosier Helper is an Indiana Department of Transportation sponsored roving freeway service patrol, providing free assistance to motorists stranded on portions of Interstate 80-94 and Interstate 65 in Northwest Indiana, which started on August 30, 1991. This paper presents a detailed evaluation of the Hoosier Helper freeway service patrol. Specifically, the study results will include a benefit-cost ratio for each of two distinct Hoosier Helper operating scenarios: Daytime patrol and 24-h patrol. The calculation of agency cost concerns an aggregation of equivalent annual investment cost, employee salaries and benefits, overhead cost, and maintenance cost for Hoosier Helper. The following components comprise the estimation of Hoosier Helper benefit: Nonrecurrent congestion delay savings, secondary crash reduction, and vehicle operating cost savings. The study yielded a 4.71:1 benefit-cost ratio for the daytime program operation and a 13.28:1 benefit-cost ratio for the 24-h program operation. The increase in benefit-cost ratio magnitude, brought about by Hoosier Helper's change to 24-h operation, clearly supports the program's operating strategy as it exists today.

Economic Evaluation of Signal Preemption Projects

Preemption techniques are designed to provide preferential treatments to buses at signalized intersections. A preemption strategy, if properly designed, can provide continuous green phases to buses at successive intersections, thereby reducing delays and travel times along the bus-street. It can also potentially increase delays and travel times along the cross street. A procedure for economic evaluation of preemption projects is presented in this paper, followed by a case study demonstration. It is a variation of benefit-cost analysis that provides an estimate of the maximum investment that can be justified in a signal preemption project by way of savings in delay, fuel consumption, and emissions. The TRAF-NETSIM model was used to assess the operational consequences of signal preemption. The procedure is found viable and the case study results appear to be reasonable, and sensitive to changes in interest rates and project lives.

ITS Impacts on Safety and Traffic Management: An Investigation of Secondary Crash Causes

Freeway service patrols, an increasingly popular choice in combating the effects of traffic incidents on freeway operations, have been known to reduce incident response and clearance time. This reduction can help alleviate the delay due to non-recurrent, incident related congestion, as well as lower the chance of secondary crashes. While much work has been done in the direction of identifying the benefits stemming from the delay savings by freeway patrols, little has been done to identify the potential savings from lowering the likelihood of secondary crash occurrence. Using a 5-year incident data base from the Borman Expressway, we develop logistic regression models to examine what primary crash characteristics are likely to influence the likelihood of a secondary crash. The findings suggest that clearance time, season, type of vehicle involved, and lateral location of the primary crash significantly influence the likelihood of secondary crash occurrence. Further, the 1995 potential benefit from secondary crash reduction was $568,080 exceeding the 1995 Hoosier Helper freeway service patrol program costs by a factor of 1.38. Given a better understanding of what contributes to secondary crash occurrence, various components of incident management can be operated at a higher level of cost-effectiveness.

Optimum Bus Headway for Preemption: A Simulation Approach

Preemption techniques are designed to provide preferential treatment for buses at signalized intersections. A preemption strategy, if properly designed, can provide continuous green phases for buses at successive intersections, thereby reducing travel times and delays along the bus route. However, the length of delay incurred by all the vehicles in the system may be affected by the different bus headways under preemption operation. Unfortunately, no formal technique is available to assess the cumulative delay consequences of bus headways. The application of a simulation model, NETSIM, to test the effect of different headways is presented. NETSIM was selected because it can microscopically simulate vehicular movements on a street network and because an animation feature within NETSIM is available that allows the user to track an individual vehicle from the source to the sink. A major bus route in Ann Arbor, Michigan, was used as the experiment site. The major conclusions are that NETSIM can generate delay data at various levels of aggregation (e.g., link, node, and route) that can be used to assess the operational consequences of bus headways under preemption conditions. For the volume levels studied in the project, the savings in delay along the bus route resulting from preemption appears to be a good measure for determining the optimum headway.

NETSIM-Based Approach to Evaluation of Bus Preemption Strategies

Preemption techniques are designed to provide preferential treatment to buses at signalized intersections. Uncertainties resulting from variations in passenger boardings and unboardings at bus stops make the prediction of the exact arrival times of buses at intersections extremely difficult. A preemption strategy, if properly designed, can provide continuous green phases to buses at successive intersections. It is unfortunate that a validated technique that can be used to assess the possible consequences of signal preemption is not available. The authors present the application of a simulation model, NETSIM, to make such an assessment. NETSIM was selected because of its ability to microscopically simulate vehicular movements on a street network and its ability to track an individual vehicle from the source to the sink by the use of an animation feature. A major bus route in Ann Arbor, Michigan, was used as the experimental site. The major conclusions are that NETSIM, when properly validated, can generate delay and queue-related measures of effectiveness that are compatible with field data and that the animation feature of NETSIM can be used to assess the operational consequences of bus preemption on a series of intersections on a bus route. For the volume levels studied in the project, savings in delay along the bus route resulting from preemption exceed the increases in delay along the cross street. Further research is needed to determine whether the net savings in delay, when balanced against the costs of installing and maintaining the system and the inconvenience to motorists along the cross street, make the system worthwhile.