Application of license plate recognition in highway speed control system

The construction of expressways in China is not long. Considering safety factors, the maximum speed limit of expressways is generally 110-130 kilometers per hour. However, with the development of automobile technology, it is easy for small cars to drive at 150 kilometers per hour, so speeding on expressways is very common. An owner once asserted: "80% of the cars on the expressway are speeding!" A large number of speeding behaviors have brought great hidden dangers to the safety of expressway driving. In recent years, there have been continuous traffic accidents on expressways. Statistics have shown that more than 70% of expressway traffic accidents are caused by speeding. How to manage and punish speeding on expressways, encourage drivers to reduce their speed, ensure the safety of themselves and others, and protect the property safety of individuals, groups, and the country has become a serious issue facing expressway management departments.

Among various traffic violations, speeding accounts for a large proportion. As the saying goes, nine out of ten accidents are caused by speeding. Because of the high speed, it is difficult for the driver to make correct handling measures in the first time when encountering an emergency. In addition, the inertia and braking system of the vehicle cannot be perfectly controlled. From the statistics of the Ministry of Public Security on road violations in the past few years, the proportion of speeding cases and other traffic accidents remains high, and it is not difficult to see the clues. Therefore, speeding has always been considered an important factor in road traffic accidents; therefore, from the perspective of traffic law enforcement, banning speeding is one of the means to maintain traffic safety.

Fortunately, in recent years, the widespread use of "electronic police" on highways has become a "blocker" for monitoring speeding, effectively curbing speeding vehicles and reducing accidents on highways. In the case mentioned above, the radar speed meter in the intelligent traffic monitoring system played a major role. As an important part of the electronic police, the function of the speeding monitoring system is to detect and record speeding behaviors. In the speeding monitoring system, the speed measurement methods currently used in China are radar speed measurement, ground sensor coil speed measurement, video speed measurement, infrared detection and laser detection.

The ground induction coil speed measurement method was used earlier and has good detection results. This method determines whether the vehicle is speeding based on the speed of the parallel coil and takes video evidence. However, the construction work of burying the induction coil in the ground is large, and the coil needs to be reburied once the road surface changes.

Video speed measurement tracks the behavior of illegal vehicles by analyzing continuous video images, and captures illegal vehicles by analyzing and controlling the camera. This system is not limited by road conditions. It detects traffic data by setting up cameras above the road. It is a new generation of road vehicle detection method; the disadvantage is that it is difficult to identify high-speed moving vehicles. At the same time, video technology is also easily affected by light and weather.

Infrared and laser detection are theoretically feasible and have high detection accuracy. However, faced with the impact of multiple roads, multiple vehicles and multiple pedestrians at intersections, the efficiency of point measurement cannot meet regulatory requirements. Most importantly, the damage to the human body, mainly the human eye, caused by the laser beam in laser detection is an unavoidable problem. Among various speed measurement methods, radar speed measurement is undoubtedly the most suitable for highways. With the development and improvement of radar speed measurement technology itself, it is increasingly used in intelligent traffic monitoring systems for highways and urban traffic. For example, well-known transportation industry manufacturers such as Tianjin Tiandi Weiye all use radar speed measurement.

The principle of radar speed measurement is to apply the Doppler effect, so it has the following characteristics:

(1) The radar beam has a large irradiation area, so radar speed measurement can easily capture the target without precise aiming;

(2) Radar speed measuring equipment can be installed on patrol cars to detect vehicle speed while in motion, and is a very important component of the “mobile electronic police”;

(3) The radar speed measurement error is ±1km/h when fixed and ±2km/h when moving, which can fully meet the requirements for traffic violation investigation and punishment;

(4) The electromagnetic wave beam emitted by the radar has a certain angle, so the effective speed measurement distance is closer than that of laser speed measurement. The maximum speed measurement distance is 800m (for large vehicles).

(5) Radar speed gun technology is mature and reasonably priced.

(6) The beam angle of the radar speed meter is a very important technical indicator. The larger the beam angle, the more easily the speed measurement accuracy is affected; conversely, the impact is smaller.

Radar speed guns are used by my country's public security traffic management departments as the preferred tool for speeding penalties because of their low price, accurate speed measurement, ease of use and ability to detect vehicle speed while in motion.

The speeding control system is divided into two parts: the speeding detection system and the vehicle interception system. The speeding detection system completes tasks such as vehicle speed detection, license plate number recognition, and vehicle driving record; the vehicle interception system recognizes the license plates of passing vehicles to determine whether they are speeding or other blacklisted vehicles, and intercepts and punishes blacklisted vehicles.

In fact, the speeding control system that uses license plate recognition technology changes the manual interpretation of license plates to the use of license plate recognition technology to automatically identify license plate numbers, automatically construct a speeding blacklist and automatically alarm, which not only realizes the instant processing (punishment can be imposed when leaving the highway), but also greatly reduces the manual workload (no manual interpretation of license plates is required).

The on-site simulation effect diagram is shown below:

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On-site effect simulation diagram

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High-speed radar speed measurement

1. Front-end system composition

The front-end system is mainly composed of three modules: identification, speed measurement, and transmission.

1.1 Identification

Identification is the core part of the system. Tianjin Tiandi Weiye Expressway Checkpoint Radar Speed ​​Measurement System can automatically identify vehicle license plates passing through monitoring points 24 hours a day. In addition, the system also has a character self-learning function and has the ability to automatically recognize license plates of civil, police, military, armed police and other vehicles .

Administrators can enter license plate information of vehicles with a history of entering checkpoints, license plate information that traffic police and the public security need to assist in investigating, etc. into the blacklist database. When the front-end host captures a license plate on the blacklist, various voice prompts are used to provide a reminder to relevant managers.

The system can publish the license plates of speeding vehicles collected by the system in real time through variable information boards installed along the highway to remind the violating drivers to pay attention, thereby warning the speeding drivers.

1.2 Speed ​​Test

Use speed radars from various brands to provide real-time speed data of vehicles passing through.

1.3 Transmission

Transmission refers to sending information such as the vehicle license plate number and speed value obtained at the speed measurement point to the exit penalty point so that the speeding vehicle can be punished.

For Tianjin Tiandi Weiye checkpoint radar speed measurement system and many large manufacturers, recognition is completed at the speed measurement point, so only the recognition results, driving speed, speed measurement time and speed measurement location need to be transmitted. When evidence is required, the captured pictures must also be transmitted, which greatly reduces the amount of front-end data transmission.

There are two ways to transmit data: uploading all vehicle records and uploading speeding vehicle records. The latter method transmits a smaller amount of data, but it is necessary to consider the consistency with the speeding standards with the back-end management software. Although the former method has a larger amount of data, since all vehicle records are transmitted to the back-end management system, it provides considerable flexibility for instantly changing speeding limit standards and setting multiple blacklists.

2. Penalty points at toll booths

The equipment is installed on the toll boat island of the toll station. It can also capture and identify vehicles leaving the toll station, or use manual identification to inspect speeding vehicles and punish speeding vehicles. If the method of capturing and identifying vehicles leaving the toll station is adopted, since the vehicles at this position are relatively stationary, the video trigger capture method can be used to greatly reduce the construction cost. More importantly, the same vehicle can realize the function of interval speed measurement at the same time according to the time taken from the speed measurement point to the toll station. The schematic diagram is as follows:

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System Diagram

3. High-speed lane checkpoint

A new round of intelligent transformation of highways has quietly begun. In the future, whoever can provide high-quality and efficient management and an unimpeded traffic environment will win huge economic benefits brought by the rolling traffic; whoever can adopt advanced intelligent transportation technology to serve management will be able to strategize in modern traffic management.

From this point of view, the high-speed speed measurement system based on license plate recognition has broad market application prospects and strong vitality, and will surely shine in the market for intelligent transformation of highways.