2013 Session: 841

• Validation of Macroscopic Lane-Changing Model
  Abstract: Systematic lane changes inside a weaving area could disrupt the whole traffic flow and, even lead to accidents. Recently, a macroscopic lane-changing model was proposed to model traffic dynamics inside the lane-changing area at a merging section. But this macroscopic lane-changing model hasn’t been validated with vehicle trajectory data. In this paper, we attempt to fill this gap. Lane changes are categorized into two types: left lane changes and right lane changes. Inside the lane-changing area, with the assumptions that traffic is fully balanced and all left lane changes are induced by on-ramp vehicles, two linear relations are derived: (i) the number of left lane changes within two adjacent lanes linearly increases from the leftmost lane to the shoulder lane; (ii) the total number of left lane changes is proportional to the flow-rate of on-ramp vehicles inside the lane-changing area. Detailed studies are presented for different time periods and road geometries by using NGSIM vehicle trajectory data. Validation results confirm that these two linear relations do exist. In addition, capacity reductions caused by the lane changes of weaving vehicles can be observed in the fundamental diagram of lane-changing traffic. This study helps to understand the macroscopic lane-changing traffic behaviors and sheds light on developing possible macroscopic lane-changing traffic flow models and ramp-metering and lane management strategies.
  Authors: Gan, Qijian; Jin, Wen-Long
  Authors: Gan, Qijian; Jin, Wen-Long
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-2866
• Empirics of a Generalized Macroscopic Fundamental Diagram for Urban Freeways
  Abstract: Due to increasing exchange of data between measurement sites, the area over which traffic control is applied increases. This leads to three new challenges: (1) working with the large quantities of data (transmit, store), (2) estimating the traffic state, (3) controlling a large area with many controllers (and hence large solution space). This paper introduces a new way of describing the traffic state for a large area, which requires much less data and nevertheless gives an accurate representation of the state.The Macroscopic Fundamental Diagram (MFD) which links the production, i.e. the average flow, to the accumulation, i.e. the average number of vehicles in an area. This paper shows that this can be generalized to a generalized macroscopic fundamental diagram (GMFD) for urban freeways, which relates the production to the accumulation and the spatial spread of density. Analysis of 10 months of data of the Amsterdam ring road freeway shows that this is a continuous function, which increases and decreases with accumulation like a fundamental diagram, and decreases with the spatial spread of density. The predictive performance is tested by using a non-parametrized fit and by fitting a functional form, which perform equally well. Predicting the production is important especially near the maximum production. The GMFD explains much more of the spread in the production than the MFD, especially near this maximum production. Thus, this lean traffic state description can be used in a setting a target for traffic control.
  Authors: Knoop, Victor L.; Hoogendoorn, Serge
  Authors: Knoop, Victor L.; Hoogendoorn, Serge
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-3744
• Empirical Characterization and Interpretation of Hysteresis and Capacity Drop Phenomena in Freeway Networks
  Abstract: The objective of this study is to characterize hysteresis and capacity drop phenomena in freeway networks using commonly-available loop detector data from three different networks: Chicago (Illinois), Portland (Oregon), and Irvine (California). To explore the effects of variation in network topology and size on the network fundamental diagram (NFD), a comparison is made using the observed flow-occupancy diagrams of the selected freeway networks. The results provide further confirmation that findings presented in the literature for a limited number of networks are also valid for other freeway networks not previously studied. It is observed that freeway networks are more likely to exhibit an inconsistent hysteretic pattern in terms of shape and size depending on the spatial distribution of congestion over the network. Based on empirical observations, hysteresis loops are characterized by their shape and size. In this paper, two shapes are identified, characterized and named as H1 and H2. Also, it is proposed that the size of each hysteresis loop can be characterized by its width, height and the area covered by the hysteresis loop. It is postulated that the capacity drop phenomenon exists in freeway networks in a similar manner to individual freeway sections. Two types of capacity drop are identified. Capacity drop type I is associated with the inability of the freeway network to sustain its throughput at its peak value for a relatively long time and therefore, capacity drops while demand is still high and network is loading. Capacity drop type II is associated with the instability of network traffic when the network undergoes reloading (e.g. afternoon peak period) after an incomplete recovery from the initial loading (e.g. morning peak period). In some cases, this results in a lower capacity in the afternoon compared to the morning. Empirical results show that the observed phenomena are reproducible on different days and for different networks.
  Authors: Saberi, Meead; Mahmassani, Hani S.
  Authors: Saberi, Meead; Mahmassani, Hani S.
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-2391
  Practice-Ready: Yes
• Validation of Macroscopic Lane-Changing Model
  Authors: Gan, Qijian
  Authors: Gan, Qijian
  Year: 2013
  Document Type: Presentation
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-2866
• Empirical Characterization and Interpretation of Hysteresis and Capacity Drop Phenomena in Freeway Networks
  Authors: Mahmassani, Hani
  Authors: Mahmassani, Hani
  Year: 2013
  Document Type: Presentation
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-2391
• Empirics of a Generalized Macroscopic Fundamental Diagram for Urban Freeways
  Authors: Knoop, Victor
  Authors: Knoop, Victor
  Year: 2013
  Document Type: Presentation
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-3744
• Speed Harmonization: Effectiveness Evaluation Under Congested Conditions
  Authors: Mahmassani, Hani
  Authors: Mahmassani, Hani
  Year: 2013
  Document Type: Presentation
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-4247
• Speed Harmonization: Effectiveness Evaluation Under Congested Conditions
  Abstract:

  The objective of this paper is to explore the impacts of early shockwave detection on breakdown formation and driving hazard (safety) and the possible corresponding improvements using speed harmonization as a control strategy. When a highway is operating at near-capacity, shockwaves may appear and propagate because of frequent lane changing/merging maneuvers or sudden car decelerations. The shockwave formation may eventually result in a traffic breakdown, a travel delay increase, a throughput decrease and more importantly unsafe driving situations. Speed harmonization is an Active Traffic Management (ATM) strategy that aims at avoiding shockwave formations, and minimizing incident related hazards by controlling vehicular speeds and creating a more uniform traffic flow. Several efforts have been made to evaluate the speed harmonization systems using different traffic micro-simulation models. However, further related behavioral-based studies are needed, especially with the development of the Connected Vehicle technology. The adopted approach relies on a cognitive risk-based microscopic simulation model capable of endogenously accounting for incidents to study the effects of speed harmonization strategies on the traffic flow characteristics and safety. A wavelet transform based algorithm – to detect the shockwave formation – is combined with a reactive speed limit selection algorithm to implement the speed harmonization within the microscopic simulation model. Three sets of scenarios are simulated and the results show significant improvement in traffic flow characteristics through the implementation of the speed harmonization control strategy under congestion conditions. A fundamental diagram analysis reveals the existence of an “optimal” location to implement the speed limit changes upstream of the shockwave detection point. The analysis also reveals the importance of speed limit compliance for the success of a speed harmonization system

  Authors: Talebpour, Alireza; Mahmassani, Hani S.; Hamdar, Samer Hani
  Authors: Talebpour, Alireza; Mahmassani, Hani S.; Hamdar, Samer Hani
  Year: 2013
  Document Type: Paper
  Subject: Operations and Traffic Management
  Session: 841
  Paper Number: 13-4247