单片机控制的简单计算器外文文献(2)

第二篇范文：英文文献单片机

Abstract. Traffic in urban areas is generally regulated by traffic lights, which

represent a traffic flow bottleneck if they are not effectively configured. The dynamic nature of traffic flows makes reliable prediction possible only over a limited time horizon, and hence necessitates continual re-computation solutions. As intersections network size increases, the exponential growth in joint signal timing and traffic states exhibit a computational barrier to determining effective traffic lights timing. So, real-time traffic signal control optimization becomes a challenging problem. The present work investigates the issue of adaptive traffic control using real-time traffic data in multiple intersections. Each network intersection is controlled by an

autonomous agent operating with a view of incoming traffic. The generated model presents ability to identifying dynamic changes in traffic flow conditions as well as adjusting green lights sequences and offering a good coordination between each

intersections neighboring. The main contribution of this model is a real-time adaptive control of the traffic lights, according to discontinuity and heterogeneity of traffic flow. Simulation results confirm the system effectiveness compared to fixed time control, actuated time control and green wave method. And that by mitigating the congestion in terms of maximum throughput traffic flow, minimum waiting time and stops while maintaining fairness among all the network traffic lights. Keywords: Traffic lights control, multiple intersections, adaptive, self-organizing, coordination

1. Introduction

Traffic congestion has become a crucial problem especially in urban locations. This is due to the incapacity of roads to satisfy the expectations of an exponential vehicles number. The consequences are significant costs in terms of man hours lost, excessive fuel consumption, and also an adverse environmental effect through carbon emissions. Thus, congestion reduces the quality of life for many people and represents a major handicap for the road transport system. Nevertheless, it remains the displacement means most used of citizens.

Traffic lights are the key element of traffic control. The combination of several

constraints makes harder to design an effective traffic light control strategy to achieve an optimal real time schedule.

This is especially the case of multiple intersections scenarios since traffic conditions from neighboring intersection have a dynamic impact on the local traffic lights.

Indeed, these flows should become part of the local traffic flow after a certain period. Therefore, the coordination between adjacent intersections should also be taken into account.

Existing methods for traffic lights management can be grouped into three categories: fixed time control,actuated control and adaptive control.

Fixed time control is the most commonly implemented control strategy in the real word. The timing signal is previously calculated based on traffic conditions studied

which is provided by day of week and time of day. A large amount of historical traffic data needs to be collected, recorded and then used to derive some traffic patterns. This is based on different geographic location of intersections and different time periods (e.g.,peak hours).However, these systems cannot be effective because the traffic conditions may change dynamically and significantly from time to time throughout the day. It is only applicable in stable traffic conditions.

The other scheme, called a traffic actuated controller, works by adapting to the volume of vehicles on the road. It does not set a timer for the cycle of signals, but instead measures the volume of vehicles on the road at any given moment and then sets the frequency and interval of traffic lights accordingly. Actuated traffic signal provides a minimum length of green time to each approach during a cycle. This length may be incremented based on vehicle arrivals. The length of every green interval is also constrained by a maximum green time specification.

Compared to fixed time control, actuated control is based on online data which is collected via traffic sensors, as induction loops or infrared sensors that report measurements to a central entity. These traffic volumes data are transferred to the signal control system to decide. However, the variability and unpredictability of

traffic demand on arterial systems often outpace the ability to update signal timings so that signalized intersections operate efficiently.

In the other hand, adaptive traffic control covers a set of techniques which provide a systematic approach for automatic adjustment of traffic lights states in real time. The system aim is to achieve and to maintain a desired level of control system

performance when traffic parameters change in time.

A large variety of adaptive traffic tools have been developed. Thus, the conventional green wave mechanism has been widely used in many cities. It is a traffic control strategy which assigns a fixed offset to a sequence of traffic lights such that if vehicles travel at a certain velocity from specified junction to others, they will not stop at any red lights. The offset is the time needed for vehicles to travel from an …… 此处隐藏：3264字，全部文档内容请下载后查看。喜欢就下载吧 ……