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Browsing by Author "Zhang, Yufeng"

Now showing 1 - 4 of 4
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    After Study of The Bus Rapid Transit A Line Impacts
    (Center for Transportation Studies, University of Minnesota, 2018-12) Tomhave, Benjamin; Zhang, Yufeng; Khani, Alireza; Hourdos, John; Dirks, Peter; Olsson, Jack; Tao, Tao; Wu, Xinyi; Cao, Jason
    In response to the limited awareness surrounding Bus Rapid Transit (BRT) and the A Line, this study provides answers to questions regarding the operation and public perception of the A Line in the Twin Cities region, Minnesota. Two traffic scenarios were studied, one for high-volume oversaturated traffic during the Minnesota State Fair, and a second for normal operating conditions. For both scenarios, intersection queue length and traffic flow rate were compared before and after an A Line bus. It was found that in both time periods (Fair and non- Fair), the dwelling of an A Line bus during a green traffic signal did not have a statistically significant impact on intersection queue length or traffic-flow rate at either of the two researched stations. From an analysis of the 2016 On-Board Survey, it was determined that passengers are more satisfied by the overall service of the A Line than local buses while there is not a significant difference in overall satisfaction compared to express buses, light rail and commuter rail. The top three important service attributes to overall satisfaction are “paying my fare is easy,” “hours of operation,” and “handling of concerns/complaints.” It is recommended that the transit agency improve the attributes that have higher relative influences and lower mean performances. Based on this criterion, the attributes that should be given priority are “shelter/station conditions and cleanliness” and “behaviors of other passengers and atmosphere on board.”
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    An Algorithm for Reliable Shortest Path Problem with Travel Time Correlations
    (2019-02) Zhang, Yufeng
    Reliable shortest path (RSP) problem reflects the variability of travel time and is more realistic than standard shortest path problem which considers only the average travel time. This thesis describes an algorithm for solving the mean-standard deviation RSP problem considering link travel time correlations. The proposed algorithm adopts the Lagrangian substitution and covariance matrix decomposition technique to deal with the difficulty resulting from non-linearity and non-additivity of the Mixed Integer Non-Linear Program (MINLP). The problem is decomposed into a standard shortest path problem and a convex optimization problem whose optimal solution is proved and the Lagrangian multipliers ranges are related to the eigenvalues of the covariance matrix to further speed up the algorithm. The complexity of the original problem is notably reduced by the proposed algorithm such that it can be scaled to large networks. In addition to the sub-gradient Lagrangian multiplier updating strategy integrated with projection, a novel one based on the deep-cut ellipsoid method is proposed as well. Numerical experiments on large-scale networks show the efficiency of the algorithm in terms of relative duality gap and computational time. Besides, there is evidence showing that, though having longer computational time, the ellipsoid updating method tends to obtain better solutions compared with the sub-gradient method. The proposed algorithm outperforms the existing one-to-one Lagrangian relaxation-based RSP algorithms and the exact Outer Approximation method in the literature.
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    Analysis of Interstate 405 Traffic Data and Performance Measures, and Recommendations to Improve Corridor Performance
    (2018-01-25) Schmit, Matt; Khani, Alireza; Zhang, Yufeng; zhan4879@umn.edu; Zhang, Yufeng; University of Minnesota, Department of Civil, Environmental, and Geo-Engineering; University of Minnesota, Humphrey School of Public Affairs
    This study reflects findings from an independent and objective analysis of traffic data pertaining to performance of Washington’s I-405 tolled corridor. Researchers were asked to describe where the I-405 express toll lane (ETL) facility is working and where it is underperforming by analyzing the accuracy, utility, and limitations of available and applicable traffic data. Further, researchers were asked to compare findings against relevant performance measures contained in state statute. The researchers did a comprehensive study on the speed, volume and travel time on ETLs and General purpose lane (GPLs) based on the loop detector data and transaction data. The conclusions were drawn from the analysis. This data repository hosts the final report of the study as well as all the direct data analysis results that were not able to be included in the report due to length limit, for public sharing and data reuse purpose.
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    On the Planning and Operations of the Integrated Transit and Mobility-as-a-Service Transportation System: An Equilibrium Analysis Approach
    (2021-07) Zhang, Yufeng
    Public transportation system not only carries a massive volume of passengers, providing people access to jobs, services, resources, and opportunities but also bears the mission of promoting transportation equity and justice. In the era of rapid informational and vehicular technologies’ development and commercialization, the transportation system is going through a paradigm shift. The shift is symbolized by the birth and growth of the Mobility-as-a-Service (MaaS) system. Its emergence greatly enhances urban mobility by relieving travelers from the strait where traveling is almost equal to owning a personal vehicle or being able to drive. Instead, travel is made into a service that can be provided when needs arise. Under the influence of MaaS, transit services are facing the challenge of ridership decline and the waste of investment. However, opportunities also surface as the idea of public-private partnership is exemplified by the integration of transit and the MaaS system. Although been implemented in practice, the integrated system has not received enough research attention. Existing research oftentimes focuses on either transit or MaaS system and studies the problem within each subsystem independently. The interaction between service providers – transit and MaaS agencies – is largely overlooked, let alone the interaction between service providers and travelers. This dissertation employs an equilibrium analysis approach to derive some knowledge about the planning and operations of the integrated system. Three relatively independent but interconnected studies collectively shed some light on the issue. First, a general demand and supply equilibrium analysis is conducted to gain some basic understandings of the system. Through the modeling of the interactions between the service vehicle drivers and the integrated system riders, key system properties such as decreasing returns to scale and potentials of subsidizing trips are illustrated. Second, a closer look into the demand side equilibrium is cast. By employing a mixed complementarity program describing travelers’ mode and route choice equilibrium behavior, the idea of providing path-based monetary incentivisation is specifically examined. It is found that the mere introduction of the integrated mode can significantly reduce vehicle miles traveled, but the total system travel time can increase or decrease depending on the demand level. Nevertheless, the aspiring finding that the integrated trips take place mostly in areas with limited or no transit services indicates that the integration can be a good complement to the transit system. Third, an operational level study from the mobility service provider’s perspective is carried out. A multi-epoch driverless vehicle fleet rebalancing and dynamic pricing optimization problem is established to capture the leader-follower nature. By anticipating travelers’ mode choice decisions, a mobility service provider sets the price level and relocates idle autonomous vehicles to service riders. With the net revenue maximization operation objective, the improvement of the total revenue generated by the proposed policy is confirmed by comparing with that of a myopic policy. In terms of system performance, it is found that the MaaS operator tends to service regions with good transit coverage while leaving transit-deficient areas under-served. This dissertation gains insights into the integrated system in both the aggregated level for making long-term planning decisions and disaggregated level for developing short-term operational strategies. The acquisition of such insights is critical because both city planners and service providers can draw on and learn from the theoretical research outcome and inform the policy- and decision-making for paving the way for the future transportation system.