Congestion Hotspots Research Articles

Performance Measures to Characterize Corridor Travel Time Delay Based on Probe Vehicle Data

Anonymous probe vehicle data are being collected on roadways throughout the United States. These data are incorporated into local and statewide mobility reports to measure the performance of highways and arterial systems. Predefined spatially located segments, known as traffic message channels (TMCs), are spatially and temporally joined with probe vehicle speed data. Through the analysis of these data, transportation agencies have been developing agencywide travel time performance measures. One widely accepted performance measure is travel time reliability, which is calculated along a series of TMCs. When reliable travel times are not achieved because of incidents and recurring congestion, it is desirable to understand the time and the location of these occurrences so that the corridor can be proactively managed. This research emphasizes a visually intuitive methodology that aggregates a series of TMC segments based on a cursory review of congestion hotspots within a corridor. Instead of a fixed congestion speed threshold, each TMC is assigned a congestion threshold based on the 70th percentile of the 15-min average speeds between 02:00 and 06:00. An analysis of approximately 90 million speed records collected in 2013 along I-80 in northern New Jersey was performed for this project. Travel time inflation, the time exceeding the expected travel time at 70% of measured free-flow speed, was used to evaluate each of the 166 directional TMC segments along 70 mi of I-80. This performance measure accounts for speed variability caused by roadway geometry and other Highway Capacity Manual speed-reducing friction factors associated with each TMC.

Identifying house price effects of changes in urban street configuration: An empirical study in Nanjing, China

We explore the proposition that the fast continuous changes in urban street network associated with urban growth and the attendant changes in accessibility are partial determinants of micro-level house price movement. To test this hypothesis we examine the dynamic relationship between urban configuration and house price in the short-run from 2005 to 2010, taking the case of the city of Nanjing, China. A spatial-network analysis method is employed to track changes in accessibility within the urban street layout over time. The results provide evidence that changes in urban configuration are statistically associated with housing market changes. As the city’s road grid changes through suburban expansion, new highways and internal adaptation, changes in relative accessibility follow, both locally and throughout the whole city. Generally, improved accessibility leads to higher property prices as expected. But we also find a negative relationship where new congestion hot spots are created and we identify several types of systemic spill-over effects.

Virtual machine placement optimizing to improve network performance in cloud data centers

With the wide application of virtualization technology in cloud data centers, how to effectively place virtual machine (VM) is becoming a major issue for cloud providers. The existing virtual machine placement (VMP) solutions are mainly to optimize server resources. However, they pay little consideration on network resources optimization, and they do not concern the impact of the network topology and the current network traffic. A multi-resource constraints VMP scheme is proposed. Firstly, the authors attempt to reduce the total communication traffic in the data center network, which is abstracted as a quadratic assignment problem; and then aim at optimizing network maximum link utilization (MLU). On the condition of slight variation of the total traffic, minimizing MLU can balance network traffic distribution and reduce network congestion hotspots, a classic combinatorial optimization problem as well as NP-hard problem. Ant colony optimization and 2-opt local search are combined to solve the problem. Simulation shows that MLU is decreased by 20%, and the number of hot links is decreased by 37%.

Adaptive Load Balancing Based on IP Fast Reroute to Avoid Congestion Hot-spots

Several load balancing techniques for IP routing scheme have appeared in the literature. However, they require optimization process to compute optimal paths to meet traffic demand so that it requires a mechanism to measure traffic demand and to share them among all routes in order to follow dynamics of traffic. It naturally results in communication overhead and losing sensitivity to follow traffic dynamics. In this paper, we investigate a load balancing mechanism from another approach, i.e., based on IP fast reroute mechanisms. The main idea is simply to forward packets into detour paths supplied by IP fast reroute mechanisms only when packets meet congestion. This strategy enables us to use vacant resources adaptively as soon as they are required to avoid and dissolve the congestion. Through traffic simulation we show that IP fast reroute based load balancing mechanisms improve the capacity of networks.

A spatially explicit network science model for emergency evacuations in an urban context

Emergency evacuations are essential for protecting humans from hazardous events such as wildfires, tsunamis, hurricanes, and industrial accidents. In urban regions, effective emergency management is highly dependent on reliable knowledge about potential traffic congestion hotspots that can arise during an evacuation. Spatially explicit models that combine network science and optimization techniques within a Geographic Information System (GIS) can target the unique physical, biological, and social characteristics of an area to provide more locally relevant evacuation traffic congestion predictions. The objective of this study is to design and implement the Network Science Emergency Evacuation Model (NetSEEM) using spatially explicit network science principles. The NetSEEM design is theoretically robust and can be adapted for different geographic areas and hazard types to represent the specific complexity of emergency evacuation situations. The developed NetSEEM model is applied to four evacuation scenarios in the City of Burnaby, BC, Canada. The results show expected congestion patterns at the major transportation intersections, and highlight NetSEEM as an exploratory management tool to anticipate and mitigate traffic congestion during context-dependent emergency evacuations.

Ripple: A Robust and Effective Routability-Driven Placer

The significant mismatch between the objective of wirelength and routing congestion makes the routability issue even more important in placement. In this paper, we describe a routability-driven placer called Ripple. Each step, including global placement, legalization, and detailed placement, is made to trade-off between routability and wirelength. We propose a robust and effective flow by using cell inflation to relieve routing congestion. Cell inflation has traditionally been used to deal with congestion and we will discuss how this technique can be used easily and robustly in the global placement. Besides, unlike many previous works that focus on different types of swapping strategies, we analyze and propose some simple and effective approaches when considering routability in the legalization and detailed placement steps. Experimental results show that Ripple is particularly effective in improving routability. When compared to the top results in the ISPD 2011 Contest and SimPLR, Ripple can obtain the smallest overflow and half-perimeter wirelength on average, while the congestion hot spots are also distributed sparsely in Ripple.

Metrics to Characterize Airport Operational Performance Using Surface Surveillance Data

Detailed surface surveillance datasets from sources such as the Airport Surface Detection Equipment, Model-X (ASDE-X) can potentially be used to analyze airport operations, in addition to their primary purpose of enhancing safety. This paper describes how surface surveillance data can be used to measure airport performance characteristics in three different ways: charactering surface flows, including identification of congestion hotspots, queue dynamics and departure throughput; developing metrics to evaluate the daily operational performance; and developing metrics to gauge long-term performance across different runway configurations and operating conditions. The proposed metrics have been developed with active feedback from operations personnel at Boston Logan International Airport, and are therefore evaluated and discussed using this airport as an example. These metrics can provide useful feedback on operational performance to airport operators, and, therefore, have the potential to improve the efficiency of surface operations at airports.

Time to Excise Fuel Duty?

Taxes comprise 60 per cent of the cost of a litre of petrol or diesel. Fuel duty will contribute about £33 billion to the Treasury in 2012 (Including the VAT charged on the fuel duty (see HM Treasury, 2012).Currently, revenues from fuel duty and road tax exceed expenditure on roads by £30 billion per annum. Investment in road improvements has collapsed over the last twenty years. Fuel duty is higher in the UK than in any other major economy. Taxes on diesel for commercial use are particularly high, over 50 per cent higher than in France and Germany and over 500 per cent higher than in the USA. Industries heavily dependent on road transport in the UK are therefore at a major competitive disadvantage. High fuel prices hamper just about every economic activity by raising the costs of trade. Fuel duty will tend to reduce economic output by lowering labour mobility, preventing economies of scale, and hindering competition and specialisation. Motoring taxes may also increase welfare dependency by raising travel-to-work costs, meaning many potential workers may be better off on welfare benefits than entering employment. Fuel duty discriminates against residents and businesses in rural, semi-rural and suburban areas. It represents a transfer of resources to those inner city areas which receive a disproportionate amount of the general government spending funded by motoring taxes. Poorer motorists are hit particularly hard by fuel duty. Road fuel accounts for almost 10 per cent of spending by car-owning households in the bottom decile. Motorists and hauliers are treated unfairly by the tax system. Other activities with negative environmental effects are taxed at much lower rates than private road transport. Trains and buses – which also produce significant noise and air pollution – benefit from tax breaks and subsidies. Fuel duty is a very inefficient way of addressing the wider costs associated with road transport. The amount paid bears little relation to congestion levels, accidents, infrastructure costs and local environmental impacts. Many of the economic costs associated with road transport are in reality the result of a long history of misguided government interventions in transport and land markets. For example, planning policies continue to encourage the development of brownfield sites close to busy roads, despite the obvious implications for exposure to noise and air pollution. A number of policy measures should be implemented to reduce fuel duty: In the short term, the planned 3p increase in fuel duty should be cancelled. In the medium term, a fuel duty ‘downward escalator’ should be introduced, to bring about gradual reductions in the tax over a number of years. The EU-imposed minimum price, currently 29p a litre for petrol, would be a realistic target. (Minimum tax rates are imposed by the EU Energy Taxation Directive)An alternative target, in the absence of EU regulation and in the context of current climate change targets, would be to set fuel duty according to ‘social cost’ of carbon estimates contained in the Stern Review or other studies. In the longer term, the government should aim to abolish fuel duty. These measures could be financed as follows: To cancel the planned 3p rise, about £1.5 billion per annum should be cut from government spending on counterproductive traffic management schemes and loss-making public transport services. To halve duty to 29p per litre, over a longer period, uneconomic projects such as High Speed 2 should be cancelled and train/bus operating subsidies phased out (saving in total about £11 billion p.a.). In addition, limited peak-time road pricing should be introduced in congestion hotspots with part of the revenues used for road improvements. A consistent approach to environmental taxation could also be considered, raising £5.5 billion p.a. from charging full-rate VAT on domestic heating and power. (Deregulation of the energy sector would mitigate the impact on consumers (see Wellings, 2011b).The privatisation of the road network would facilitate the abolition of fuel duty. The flotation of motorways and trunk roads would raise approximately £150 billion, which would be used to make large cuts in fuel duty. Government spending on transport would then be phased out, saving about £20 billion p.a. Finally, general tax revenues would increase markedly due to substantial efficiency gains, including much lower levels of congestion. This process is set out in much more detail in Knipping and Wellings (2012). Abolishing fuel duty would require the EU Energy Taxation Directive to be rescinded.

Generating Revenue to Fund Public–Private Partnerships for Reconstruction of Freeway Systems in Metropolitan Areas

The multimodal expressway concept proposed in this study involves creating a network of high-occupancy toll (HOT) lanes and managing traffic at greater distances from the congested hot spots to relieve the flow-exacerbating impacts on the hot spots. Modal choices for customers are created along with pricing and parking strategies. HOT lanes would not only serve cars but would also become bus rapid transit lanes. Managers would be able to use real-time pricing, speed controls, modal shifts, and information systems to regulate traffic flows throughout the region. The HOT-lane network would be created by reconfiguring the existing freeway footprint to accommodate new HOT lanes by using a portion of the left and right shoulders and restriping of regular lanes into narrower lanes if needed, along with creation of emergency pull-off areas. To encourage transit, the HOT lanes would have a progressively increasing passenger mile performance measure in a public–private partnership agreement. Sketch-planning analysis is used to assess the potential of this strategy to address funding needs for public–private partnerships for freeway reconstruction in a prototypical large U.S. metropolitan area. Potential public concerns about tolls and ways to address them are also discussed. The results from the case study sketch-planning analysis suggest that revenue from the HOT-lane network, when supplemented with revenue generated through gas taxes and other fees paid by users of the highway network, would be sufficient to pay for the reconstruction of the freeway system in the case study area.

Effective Estimation Method of Routing Congestion at Floorplan Stage for 3D ICs

Higher integrated density in 3D ICs also brings the difficulties of routing, which can cause the routing failure or re-design from beginning. Hence, precise congestion estimation at the early physical design stage such as floorplan is beneficial to reduce the total design time cost. In this paper, an effective estimation method of routing congestion is proposed for 3D ICs at floorplan stage. This method uses synthesized virtual signal nets, power/ground network and clock network to achieve the estimation. During the synthesis, the TSV location is also under consideration. The experiments indicate that our proposed method had small difference with the estimation result got at the post-placement stage. Furthermore, the comparison of congestion maps obtained with our method and global router demonstrates that our estimation method is able to predict the congestion hot spots accurately.

A smart market for passenger road transport (SMPRT) congestion: An application of computational mechanism design

To control and price negative externalities in passenger road transport, we develop an innovative and integrated computational agent-based economics (ACE) model to simulate a market oriented ‘cap’ and trade system. (i) First, there is a computational assessment of a digitized road network model of the real-world congestion hot spot to determine the ‘cap’ of the system in terms of vehicle volumes at which traffic efficiency deteriorates and the environmental externalities take off exponentially. (ii) Road users submit bids with the market-clearing price at the fixed ‘cap’ supply of travel slots in a given time slice (peak hour) being determined by an electronic sealed bid uniform price Dutch auction. (iii) Cross-sectional demand data on car users who traverse the cordon area is used to model and calibrate the heterogeneous bid submission behaviour in order to construct the inverse demand function and demand elasticities. (iv) The willingness to pay approach with heterogeneous value of time is contrasted with the generalized cost approach to pricing congestion with homogenous value of travel time.

Power-Stepped Protocol: Enhancing Spatial Utilization in a Clustered Mobile Ad Hoc Network

While most previous studies on mobile ad hoc networks (MANETs) rely on the assumption that nodes are randomly distributed in the network coverage area, this assumption is unlikely to hold, as nodes tend to be cluttered around hot spots like the site of an accident or disaster. We refer to this as a clustered layout. Intuitively, a MANET with the clustered layout may suffer from serious performance degradation due to the excessive collisions in congested hot spots and space underutilization of sparse areas. In this paper, we propose a power-controlled network protocol, called the power-stepped protocol (PSP), that maximizes the spatial utilization of limited channel bandwidth. Using a number of discrete power levels available for the underlying wireless network hardware, PSP finds the appropriate power level for each node in a distributed and a coordinated manner without causing any serious problem at the medium access control and network routing layers. A unique feature of this approach is the use the chosen radio power for both data and control packets, and thus, it requires neither any special mechanism (e.g., a separate control channel) nor frequent power adjustments. Our extensive ns-2-based simulation results have shown the proposed PSP provides excellent performance in terms of packet delivery ratio and delay, as well as the network capacity.

Internet traffic engineering

The main goal of Internet traffic engineering is to efficiently optimize the performance of operational networks in order to avoid the well-known shortcomings of the typical destination-based IP routing. Traffic engineering attempts to reduce or even avoid congestion hot spots and to improve resource utilization across the backbone IP network. During the last years traffic engineering has become an inevitable tool concerning performance optimization in large Internet backbones. The core objective of this paper is to give an overview of the architectures and mechanisms for traffic engineering.

Theoretical performance analysis of mirroring World Wide Web sites

Popular World Wide Web sites can often cause congestion hot spots in the network, resulting in degradation of performance. Typically, such sites are mirrored in order to alleviate bottlenecks. This presents users of these sites with a choice of where to access their documents. Using a theoretical Web access delay model, a performance analysis is carried out which shows the effects of mirror location and communication facility speed. The analysis shows the conflict of interest between the network operator trying to optimise aggregate data rates and that of the users trying to maximise their own individual data rates. The results reflect upon the load balancing policies for optimal network performance.