Improving Traffic Flow Characteristics by Suppressing Shared Taxis Maneuvers

The sudden maneuver of shared taxi through lanes in order to pick-up and drop-off passengers and asking their destinations -due to lack of designated stop locations- may lead to disorder in traffic flow. The main hypothesis in this research was that shared taxis sudden maneuvers and lane changings have negative effects on traffic flow characteristics and subsequently, suppressing these maneuvers will improve traffic flow characteristics. For this purpose, a study was done on a path in the city of Isfahan in Iran. First the investigated path simulated without shared taxi sudden maneuvers and then the outputs of this simulation were compared to the real measurement data. By this comparison, some differences were observed. The shared taxis maneuvers were added to simulation to see if the observed difference can be lowered. By comparing the outputs of these two simulations to the real situation parameters, the considerable negative effect of this maneuvers was recognized. After observing of the mentioned maneuvers negative effect, an innovative solution – allocating a line to shared taxis and High Occupancy Vehicles - was added to suppress shared taxi maneuvers in order to improve traffic flow characteristics. By applying this scenario on current situation delay of traffic flow and delay of shared taxis decreased from 458.48 sec. to 383.01 sec. and from 506 sec. to 450 sec. respectively. Besides, traffic flow and the number of shared taxis increased from 11986 to 12980 and 663 to 718 vehicle per hour respectively

High-speed civil transport flight- and propulsion-control technological issues

Technology advances required in the flight and propulsion control system disciplines to develop a high speed civil transport (HSCT) are identified. The mission and requirements of the transport and major flight and propulsion control technology issues are discussed. Each issue is ranked and, for each issue, a plan for technology readiness is given. Certain features are unique and dominate control system design. These features include the high temperature environment, large flexible aircraft, control-configured empennage, minimizing control margins, and high availability and excellent maintainability. The failure to resolve most high-priority issues can prevent the transport from achieving its goals. The flow-time for hardware may require stimulus, since market forces may be insufficient to ensure timely production. Flight and propulsion control technology will contribute to takeoff gross weight reduction. Similar technology advances are necessary also to ensure flight safety for the transport. The certification basis of the HSCT must be negotiated between airplane manufacturers and government regulators. Efficient, quality design of the transport will require an integrated set of design tools that support the entire engineering design team

NASA rotor system research aircraft flight-test data report: Helicopter and compound configuration

The flight test activities of the Rotor System Research Aircraft (RSRA), NASA 740, from June 30, 1981 to August 5, 1982 are reported. Tests were conducted in both the helicopter and compound configurations. Compound tests reconfirmed the Sikorsky flight envelope except that main rotor blade bending loads reached endurance at a speed about 10 knots lower than previously. Wing incidence changes were made from 0 to 10 deg

Performance Analysis of Fixed Route Shared Taxi Services (Jitney) - Case Study of Tehran, Iran

The fixed route shared taxi, known as Jitney, is one of the common modes in paratransit services and covers a significant proportion of daily trips in some developing countries, including Iran. Such system, despite its disadvantages to transportation networks, has always been the most feasible solution to overcome the shortcoming in public transit supply. As a result, it has formed users’ travel habits over the decades. Therefore, it is not possible to remove or replace Jitney lines with standard services suddenly but gradually. Unfortunately, there is a distinct lack of a comprehensive method to analyze and evaluate Jitney lines neither in the literature nor in practice. In this paper, first, to fill the gap in the literature, we develop a coherent framework to analyze the performance of fixed route shared taxi lines. This framework includes several indices that make it possible to rank and classify Jitney lines from different aspects. Second, to examine the applicability of the proposed framework, we apply it to the network of taxi lines in the metropolis of Tehran. The results prove that the framework is not only applicable in measuring the system performance, but it also provides decision-makers with decision criteria to choose improvement plans or alternatives

Performance Analysis of Fixed Route Shared Taxi Services (Jitney) - Case Study of Tehran, Iran

The fixed route shared taxi, known as Jitney, is one of the common modes in paratransit services and covers a significant proportion of daily trips in some developing countries, including Iran. Such system, despite its disadvantages to transportation networks, has always been the most feasible solution to overcome the shortcoming in public transit supply. As a result, it has formed users’ travel habits over the decades. Therefore, it is not possible to remove or replace Jitney lines with standard services suddenly but gradually. Unfortunately, there is a distinct lack of a comprehensive method to analyze and evaluate Jitney lines neither in the literature nor in practice. In this paper, first, to fill the gap in the literature, we develop a coherent framework to analyze the performance of fixed route shared taxi lines. This framework includes several indices that make it possible to rank and classify Jitney lines from different aspects. Second, to examine the applicability of the proposed framework, we apply it to the network of taxi lines in the metropolis of Tehran. The results prove that the framework is not only applicable in measuring the system performance, but it also provides decision-makers with decision criteria to choose improvement plans or alternatives

Recent Sikorsky R and D progress

The recent activities and progress in four specific areas of Sikorsky's research and development program are summarized. Since the beginning of the S-76 design in 1974, Sikorsky has been aggressively developing the technology for using composite materials in helicopter design. Four specific topics are covered: advanced cockpit/controller efforts, fly-by-wire controls on RSRA/X-Wing, vibration control via higher harmonic control, and main rotor aerodynamic improvements

QUANTIFYING THE IMPACT OF TRANSPORTATION NETWORK COMPANIES (TNCs) ON TRAFFIC CONGESTION IN SAN FRANCISCO

This research investigates whether Transportation Network Companies (TNCs), such as Uber and Lyft, live up to their stated vision of reducing congestion by complementing transit and reducing car ownership in major cities. The objective of this research study is to answer the question: are TNCs are correlated to traffic congestion in the city of San Francisco? If found to be so, do they increase or decrease traffic congestion for the case of San Francisco? If and how TNC pickups and drop-offs impact traffic congestion within San Francisco? And finally, how does the magnitude of this measured command of TNCs on congestion compare to that caused by pre-existing conventional drivers of traffic and congestion change? Apart from answering these questions, it is also sought to establish a framework to be able to include TNCs, a seemingly fledgling mode of transportation but one that is demonstrably shaping and modifying extant transportation and mode choice trends, as part of the travel demand models estimated by any geographic jurisdiction. Traffic congestion has worsened noticeably in San Francisco and other major cities over the past few years. Part of this change could reasonably be explained by strong economic growth or other standard factors such as road and transit network changes. The sharp increase in travel times and congestion also corresponds to the emergence of TNCs, raising the question of whether the two trends may be related. Existing research has produced conflicting results and been hampered by a lack of data. Using data scraped from the Application Programming Interfaces (APIs) of two TNCs, combined with observed travel time data, this research finds that contrary to their vision, TNCs are the biggest contributor to growing traffic congestion in San Francisco. Between 2010 and 2016, weekday vehicle hours of delay increased by 62%, compared to 22% in a counterfactual 2016 scenario without TNCs. The findings provide insight into expected changes in major cities as TNCs continue to grow, informing decisions about how to integrate TNCs into the existing transportation system. This research also decomposes the contributors to increased congestion in San Francisco between 2010 and 2016, considering contributions from five incremental effects: road and transit network changes, population growth, employment growth, TNC volumes, and the effect of TNC pick-ups and Drop-offs. It is so done through a series of controlled travel demand model runs, supplemented with observed TNC data. The results show that road and transit network changes over this period have only a small effect on congestion, population and employment growth are important contributors, and that TNCs are the biggest contributor to growing congestion over this period, contributing about half of the increase in vehicle hours of delay, and adding to worsening travel time reliability. This research contradicts several studies that suggest TNCs may reduce congestion and adds evidence in support of a recent empirical analysis showing that their net effect is to increase congestion. This research gives transportation planners a better understanding of the causes of growing congestion, allowing them to more effectively craft strategies to mitigate or adapt to it

Understanding and addressing the resistance towards autonomous vehicles (AVs)

Autonomous vehicles (AVs) are expected to bring major benefits to transport and society. To exploit this potential, their acceptance by society is a necessary condition. However, AV acceptance is currently at stake: AVs face resistance by bystanders and local communities. Resistance can prevent the implementation and use of AVs, threatening road safety and efficiency. The present study performed a qualitative and quantitative text analysis of comments submitted by locals in San Francisco (SF) to the California Public Utilities Commission (CPUC) on the fared deployment of AVs. The results of the analysis are synthesized, and a conceptual framework explaining and predicting resistance is proposed. The framework posits that the occurrence of resistance is a direct result of the perception of threats, which is determined by individual and system characteristics, direct and indirect consequences of system use, reactions of others, and external events. AVs as threat to safety was associated with their unpredictable, and illegal driving behavior, as well as producing conflict situations. The lack of explicit communication between AVs and other road users due to the absence of a human driver behind the steering wheel negatively contributed to perceived safety and trust, especially for vulnerable populations in crossing situations. Respondents reported a negative impact on road capacity, congestion, and traffic flow, with AVs blocking other road users, such as emergency vehicles. Inaccessible vehicle design contributed to the exclusion of vulnerable groups with disabilities. The scientific dialogue on acceptance of AVs needs to shift towards resistance as the 'other' essential element of acceptance to ensure that we live up to our promise of transitioning towards more sustainable mobility that is inclusive, equitable, fair, just, affordable, and available to all.Comment: 33 pages, 3 figure

An example of requirements for Advanced Subsonic Civil Transport (ASCT) flight control system using structured techniques

The requirements are presented for an Advanced Subsonic Civil Transport (ASCT) flight control system generated using structured techniques. The requirements definition starts from initially performing a mission analysis to identify the high level control system requirements and functions necessary to satisfy the mission flight. The result of the study is an example set of control system requirements partially represented using a derivative of Yourdon's structured techniques. Also provided is a research focus for studying structured design methodologies and in particular design-for-validation philosophies