One typical application of intelligent transportation systems (ITS) is vehicle platooning where a group of vehicles travel with smaller inter-vehicle distance safely, improving energy efficiency as well as road capacity and traffic safety. Truck platooning on highways has been widely studied and showed the aforementioned effects. However, the platooning of buses in urban environments have not been investigated thoroughly in the literature. This paper examines the effects of bus platooning with respect to traffic control and energy consumption.Microscopic traffic simulations have been conducted to demonstrate that bus platooning improves the quality of service of buses and maintains the quality of the traffic flow. Subsequently, driving cycles of buses generated from the simulation study serve as input for an energy consumption analysis, showing that not only bus platooning itself result in a reduction of energy consumption but the traffic signal prioritisation for bus platooning lead to additional energy savings. I. INTRODUCTIONVehicle platooning is one typical application of intelligent transportation systems (ITS), it refers to an operational practice in which multiple vehicles follow one another closely. The intra-platoon distance is maintained shorter compared to today's practice, which leads to reduced aerodynamic drag, particularly for the vehicles in the middle of a platoon. The change in the aerodynamic drag results in reductions of energy usage, traffic congestion, and hence emissions [1-5]. A. Vehicle PlatooningModern driver assistant systems and vehicle-to-vehicle (V2V) communication enable the formation of an electronically coupled platoon [1,5,6]. The direct connection between the members of such a platoon leads to a decreased reaction time of about 0.1 seconds, which is significantly faster than the reaction time of a driver of about 2.5 seconds [1,2,[5][6][7][8]. It is thereby possible to reduce the headways within the platoon. The intra-platoon distance between the vehicles is a key performance indicator of the platooning [4].
The development of advanced technologies has led to the emergence of autonomous vehicles. Herein, autonomous public transport (APT) systems equipped with prioritization measures are being designed to operate at ever faster speeds compared to conventional buses. Innovative APT systems are configured to accommodate prevailing passenger demand for peak as well as non-peak periods, by electronic coupling and decoupling of platooned units along travel corridors, such as the dynamic autonomous road transit (DART) system being researched in Singapore. However, there is always the trade-off between high vehicle speed versus passenger ride comfort, especially lateral ride comfort. This study analyses a new APT system within the urban context and evaluates its performance using microscopic traffic simulation. The platooning protocol of autonomous vehicles was first developed for simulating the coupling/decoupling process. Platooning performance was then simulated on VISSIM platform for various scenarios to compare the performance of DART platooning under several ride comfort levels: three bus comfort and two railway criteria. The study revealed that it is feasible to operate the DART system following the bus standing comfort criterion (ay = 1.5 m/s2) without any significant impact on system travel time. For the DART system operating to maintain a ride comfort of the high-speed train (HST) and light rail transit (LRT), the delay can constitute up to ≈ 10% and ≈ 5% of travel time, respectively. This investigation is crucial for the system delay management towards precisely designed service frequency and improved passenger ride comfort.
This paper aims to evaluate the sensitivity of the proposed cooperative dynamic bus lane system with microscopic traffic simulation models. The system creates a flexible bus priority lane that is only activated on demand at an appropriate time with advanced information and communication technologies, which can maximize the use of road space. A decentralized multi-lane cooperative algorithm is developed and implemented in a microscopic simulation environment to coordinate lane changing, gap acceptance, and car-following driving behavior for the connected vehicles (CVs) on the bus lane and the adjacent lanes. The key parameters for the sensitivity study include the penetration rate and communication range of CVs, considering the transition period and gradual uptake of CVs. Multiple scenarios are developed and compared to analyze the impact of key parameters on the system’s performance, such as total saved travel time of all passengers and travel time variation among buses and private vehicles. The microscopic simulation models showed that the cooperative dynamic bus lane system is significantly sensitive to the variations of the penetration rate and the communication range in a congested traffic state. With a CV system and a communication range of 150 m, buses obtain maximum benefits with minimal impacts on private vehicles in the study simulation. The safety concerns induced by cooperative driving behavior are also discussed in this paper.
In mixed traffic, the popularity of public transport (PT) is still affected by relatively low operating speeds compared to private vehicles. To overcome this, PT priority measures have been proposed and adopted extensively. However, existing solutions such as exclusive bus lanes or traffic signal priorities are often limited in terms of available road space or large-scale feasibility. In this paper, we propose a Vehicle-to-Vehicle/Infrastructure (V2X)-based dynamic PT priority concept in mixed traffic called Virtual Right of Way (VROW). Private vehicles in front of a PT vehicle make spaces through collaborative lane changes within a dynamic clearing distance computed based on the current traffic situation. This allows a more efficient allocation of road space while still maintaining a high level of PT priority. In this paper, we evaluate the potential traffic impacts of VROW on both PT and private vehicles by conducting microscopic traffic simulations within a small urban network and a highway scenario. Comparisons with mixed traffic and other existing bus lane priority strategies, in terms of operation and safety concerns, are analyzed and highlighted. Simulation results show that VROW improves the PT operational performance with only a marginal influence on private vehicles measured by their average travel time and the number of lane changes.INDEX TERMS Dynamic bus lane, microscopic traffic simulation, traffic impact analysis, V2X.
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