Traffic lights and PLCWith economic development, increased the number of vehicles, road congestion is becoming increasingly serious, intelligent traffic lights on the emerged. At present, the world's Intelligent Transportation System will be: a huge structure, management difficulties, such as the maintenance of large inputs. In order to improve the existing traffic conditions, and to overcome the existing shortcomings of intelligent transportation system I designed analog control traffic lights in urban and rural areas of small-scale smart traffic lights. It has small size, intelligence, maintenance into small, easy to install and so on. And other intelligent transportation system compared to the system to adapt to economic and social development, in line with the current status of scientific and technological development.Intelligent traffic lights are a comprehensive use of computer network communication technology, sensor technology to manage the automatic control system of traffic lights. Urban traffic control system is used for urban traffic data monitoring, traffic signal control and traffic management computer system; it is the modern urban traffic control system command and the most important component. In short, how to use the appropriatecontrol method to maximize the use of costly cities to build high-speed roads, trunk road and the ramp to alleviate urban areas with the neighboring state of traffic congestion has become more and more traffic management and urban planning departments need to address the the main problem. Nowadays,traffic lights installed in each crossing,has becom e the most common and dredge the traffic,the most effective mea ns.The development of the society,people's consumption level unceasing enhancement,private vehicles unceasing increase.An d more cars roads are narrow road traffic is clear.So adopting e ffective method to control the traffic light is imperative.PLC intelligent control principle is the core of the control system ,PLC put the things direction or north-south direction accordi ng to quantity of vehicles,the corresponding scale what divide s class given the green light direction between north and south direction according to certain rules too long.It can realize di vides class according to a given the green cars duration scale o f maximum car release,reduce crossroads vehicles,ease traffic congestion stagnation,realize the optimal control,so as to im prove the efficiency of the traffic control system.The application of PLC is continuously,and drive to the deepeni ng traditional control test new month benefit updates.It is simple in structure,programming and high reliability etc,conveni ent already widely used in industrial processes and position in the automatic control.Due to use of PLC has the characteristics of environmental adaptable,and its internal timer is very rich in resources,but the current widely used"progressive"lights ,especially for precise control more than thecrossway control can be easily realized.So now increasingly ap plying PLC traffic light system.Meanwhile,PLC itself also has communication networking function,will the same path as part of a LAN signal unified disp atching management,can shorten the traffic wait times,realize scientific management.In real-time detection and automatic co ntrol of PLC application system,PLC is often used as a core comp onents.In the21st century,PLC will have greater development.Technic ally,the computer technology can morely new achievements usedinprogrammable controller design and manufacturing,there will b e faster,storage and larger capacity,intelligent stronger var ieties appear;Look from product size,can further to mini and s uper-large direction;Look from product compatibility,the var iety of our products will be more rich,specification more compl ete,perfect man-machine interface and complete communication equipment can better adapt to all kinds of industrial control oc casion demands;Look from the market,all countries to their pro duction of multiple products with international competition in tensifies and break,can appear a few brand monopoly internatio nal market situation,can appear international general program ming languages;Judging from the development of the network,pr ogrammable controller and other industrial control computer networking constitute a large control system is programmable co ntroller technology development direction.The current compute r distributed control system DCS has already a lot of programmab le controller applications.Along with the development of compu ter network,the programmable controller as automation control network andinternational general network will be an important part of the i ndustry and industry,the numerous fields outside play an increasing role.In China the increasing amount of motor vehicles,many big citie s like Beijing,Shanghai,nanjing and other ground appeared tra fficoverload running condition,traffic accidents problem also m ore and more serious.And because the various special vehicles( such as an ambulance,119120car,police and various special ve hicle110in emergency situations,by red under limited to traff ic bring a lot of inconvenience,even cause traffic accident.An d now,most traffic lights at the same moment will appear two or more than two direction at the same time for the green situation ,and increase the incidence of the traffic accident.Therefore ,design a kind of designed for special vehicles through and not cause any traffic accident,normal traffic control any time onl y one direction of modern intelligent traffic light green traff ic control system is urgently needed.交通灯与PLC随着经济的发展，车辆的数目不断增加，道路堵车现象日益严重，智能交通灯就应运而生了。