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Industrial Ethernet Book Issue 101 / 11
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Reading the road: license plate readers and their challenges

License plate reader technology is growing in popularity as collected information is providing a more complete comprehensive view of traffic conditions, allowing cities and states to develop more robust intelligent transportation system-level solutions.

INTELLIGENT TRANSPORTATION SYSTEMS (ITS) often reflect a city or state′s use of technology to help solve complex challenges, and a growing concern for both is knowing how many cars are on their roads at any given time.

Even more important is the need to map out the flow of traffic and adjust traffic lights accordingly. One of the most popular methods of collecting this information is by utilizing License Plate Readers (LPR) deployed throughout cities.

So far, around 14 states in the U.S. have issued legislation around the deployment and storage of LPRs and the information collected. It is also not regulated by most state ITS chapters, so it is up to individual cities how to deploy the technology and use the information they have gathered.

The captured data from the license plate reader can be utilized for more than just traffic flow mapping. Many cities are using this information to look for outdated vehicle registration or even warrants. Municipalities are not the only ones adopting this emerging technology.

Parking garages are using it to track how long a particular car was in their lot; this information is then used to advise changes to price. Toll roads are using them to know who to charge if a car did not have a registered transponder or tag. Even some banks are collecting the data to track and locate cars that need to be repossessed.

License plate readers

The number of license plate readers deployed is increasing, and so is the number of creative ways to utilize the technology. Traditionally, the license plate reader would attach to a light post at an intersection and be connected to the city′s traffic control network. One of the most common deployment methods today is placing license plate readers into police vehicles or parking monitors to inspect license plates when driving around. The license plate reader can scan the plate, reference the information against a database and report any errors much faster than someone having to enter the information manually.


Data and power can be combined to provide Power over Ethernet (PoE) functionality.

The increased efficiency of scanning a license plate for any errors leads to a larger amount of tickets issued. The revenue from the tickets can quickly cover the cost of deploying the License Plate Readers. Another typical deployment method is a mobile drop system. These systems can be in the form of a deployable enclosure or a portable trailer. Many mobile drop systems are battery powered with the option of a solar generator for longer deployments. Solar power allows for a system to be left in a location discreetly and stay operational for several hours or even days without being noticed.

A major factor for how good a License Plate Reader can be is the network used to backhaul the information and monitoring device power. The environmental conditions where these units are deployed forces industrial grade networking equipment to be used. There are three common ways to collect backhauled data to a central database. On a permanent installation, the best option is sending the information back using an Ethernet network.


PoE "keep alive" function can be setup to ping 192.168.1.2 on 30 second intervals.

These networks can either be constructed of copper or fiber optics to provide a stable high-bandwidth solution. If achieving a hardwired connection is difficult, or we are deploying a mobile application, WiFi is a standard solution. Placing multiple access points around a city will allow the cameras to be moved around as needed. WiFi solutions can have issues with latency if the network is not optimized. Bringing the info back with a cellular connection is growing in popularity, but the recurring cost can add up over time.

To simplify the installations and give the ability to monitor the status of the LPR, many manufacturers have started incorporating Power over Ethernet (PoE) on their products. PoE allows one cable to provide both the data and power needed. Commonly, managed PoE switches are used to supply this PoE connectivity. Managed switches are defined by individual user interfaces that allow remote access to the switch′s current status, and control some of its functionality.


License plate reader mounted on a police car.

If an Antaira PoE managed switch, like the LMP-1002C-SFP (10-Port Industrial PoE+ Gigabit Managed Ethernet Switch), is used to provide PoE connectivity, it provides both an ability to monitor and control the power for the LPR. Logging into the management interface of the switch can quickly show if the LPR is drawing power. However, sometimes, a unit can be drawing power but is not behaving as it should. One of the first solutions to this issue is to power cycle the unit.

Through the management interface, users can easily power cycle the unit by disabling and re-enabling the PoE function of the port attached to the LPR. A more convenient solution would be if the switch were able to power cycle the LPR automatically. Utilizing a PoE "keep alive" function, the switch can ping the LPR on a settable time interval and if, three consecutive pings drop, the switch will automatically power cycle the port attached to the LPR.


The use of 12 volt input power can be boosted to provide connectivity for PoE appliications.

The LPR is not the only device that has the option to be powered by PoE. Many times, WiFi products or cellular modems can also benefit from this technology. Using WiFi and cellular to backhaul information is a standard solution for mobile applications. Using PoE however with mobile applications can face some significant hurdles. Standard PoE uses 48-volts to power devices, most of the time this will force a PoE supplying device to require a 48-volt input.

The challenge then is finding a way to provide 48-volts in mobile environments where traditionally only 12-volts is used. An option is using an Antaira PoE switch with the "-24" functionality, like the LNP-0500-24(5-Port Industrial PoE+ Unmanaged Ethernet Switch, 12~36VDC input). These units will have an internal DC-DC converter that can use the commonly found 12-volt input and boost it to the 48-volt standard needed for PoE.

LPRs are going to grow in popularity with their increased deployment by municipalities nationwide. The collected information will provide a complete comprehension of traffic conditions and will allow cities and states to develop more robust ITS solutions. As more ITS solutions are deployed, connectivity challenges are going to present themselves and new technology will be deployed to address these problems and provide cutting edge solutions.

Application report by Antaira Technologies.


Source: Industrial Ethernet Book Issue 101 / 11
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