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back to Services & Technology list  Safety > Red Light Monitoring Printer-friendly version
DIFFERENCES IN DIGITAL AND WET-FILM CAMERAS According to the Insurance for Highway Safety, drivers who run red lights are responsible for an estimated 260,000 crashes each year. About 750 of these are fatal and the numbers are rising. Fatal crashes at intersections have risen 19% between 1992 and 1996, compared with only a 6% increase for all other fatal crashes. Running red lights and other traffic controls is the No. 1 cause of urban crashes. Experience has shown that some of the most serious personal injuries in motor vehicle collisions occur as a result of red light violations. The force of a side impact directly into the passenger compartment greatly increases the likelihood of serious personal injury. This type of collision is the type most likely to result in personal injuries. While the public concern over traffic issues was increasing, police personnel dedicated to address traffic issues tended to decrease. More and more resources were dedicated to crime reduction. Increasing fiscal constraints reduced resources to address the traffic concerns even more. After examining multiple other alternatives, several jurisdictions in the U.S. have begun to operate automated red light camera enforcement systems. The Howard County, Maryland, Police Department is one of the jurisdictions currently enforcing red light violations using automated camera technology. A typical system includes a 35-mm camera mounted on a pole that is connected to the traffic signal and sensors in the road. A brief time, usually .3 seconds after the signal turns red, the camera is activated. If the sensors then detect a vehicle failing to stop for the red signal, the camera takes two photographs. The first photo shows the vehicle prior to entering the intersection. The vehicle is then photographed in the intersection. The photos are reviewed by personnel to determine if a violation did occur. If sufficient evidence is documented in the photos, a violation notice is issued by mail. Red light camera systems have been proven to reduce collisions. A study of a red light camera system, in Victoria, Australia, documented a 32% decrease in right angle collisions. Little collision evaluation data is available in the US, as camera systems have just begun operations within the last few years. The Howard County Police currently operate 20 red light cameras and have issued over 21,000 citations since the operation began in February 1998. While it is still too early to quantify statistically significant changes in the collision rate, early indications are very positive. The first camera was installed at an intersection after it had experienced 15 collisions in 1997. After installation, this location experienced only eight collisions in 1998. More conclusive positive changes to driver behavior have already been documented. The red light violation rate has been reduced approximately 53% at the Howard County sites. Only 3.2% of individuals receiving violations have requested court trials, and more than 90% of the individuals appearing in court have been found guilty. Some jurisdictions use frontal photographs and some photograph vehicles from the rear. Other laws hold the driver of the vehicle accountable criminally similar to a citation issued by an officer in person, while others hold the vehicle owners responsible in a manner similar to parking tickets. Color film is used in some areas while others use black and white. But the consistent theme throughout the different approaches is the use of 35-mm wet film technology. As good quality digital cameras become more affordable, it is logical to look at digital cameras as the potential next generation of red light cameras. There are obvious advantages to using a digital camera in lieu of the wet film process. Real-time images could be utilized for incident detection and/or verification. The wet film process requires that personnel visit every camera location, usually on a daily basis, to retrieve exposed film and reload. The film must then be transported for processing, developed into negatives, and transported to a facility for review. The developed negative is then converted to a digital image so the image may be incorporated into a charging document. Using a digital camera allows the captured image to be transmitted directly to the review facility, eliminating the cost of the film and the personnel required for daily film handling. Should every jurisdiction trash their wet film cameras and install digital red light cameras today? As you may have guessed, there are reasons to think carefully before making such a change. Red light camera systems exist to reduce collision rates and save lives. Cameras are installed at signalized intersections with high collision experience. This makes cameras coincidentally located in some ideal locations for incident detection. Though it may help, having a small percentage of a jurisdiction’s traffic signals equipped with enforcement cameras would not likely be able to serve as the primary source of incident detection. What issues are raised if one system is used to capture evidence for court and also for incident detection? In addition to maintaining the integrity of the evidence, privacy laws often restrict access to violator images. Should all personnel in a traffic management center be required to successfully complete police background investigations? Can a remote law enforcement-operated red light camera facility be used as a partner to the traffic management center to operate as additional eyes? A remote partner of this type would not be a 24-hour-a-day operation, but could assist the center during peak drive times. How will the courts view digital image violations? The courts have become very comfortable with wet film images depicting points of evidence. Digital images are a different matter. Anyone that has surfed the Internet or watched television can attest to the ability of digital images to be manipulated. Using the current wet film system, the original 35-mm film can be produced in court to refute any potential claim that a resulting digital image was tampered with. This back-up plan does not exist in the digital red light camera system. Using an encryption system for the image transmission is an essential safeguard. Other systems are designed to identify if an image has been tampered with, but still, it doesn’t seem like hard evidence. One way to make the courts comfortable with this type of evidence is to save an identical image at the camera site as evidence each time a violation image is transmitted. This back-up image should be saved on one of the many forms of "tamper proof" data storage devices that do not allow data to be written over. Perhaps more important than the data storage technology itself is how it is handled. The data storage device should remain secured at the camera site until it has reached full capacity. When it is removed, the device should be stored as evidence and not be viewed except in cases where the integrity of the original is questioned. The documented chain of custody would show that the device was brought into court containing an image that had never been viewed by human eyes. In court, the untouched image could be compared to the violation image to refute a claim that an image was manipulated. Another issue centers on how great the image resolution is in cameras that are cost viable. All things equal, a greater field of view results in a lower image resolution. The ideal image must include a lot of information, including the intersection approach, the red traffic signal head illuminated and enough detail of the registration plate to allow it to be read with the naked eye. That can be a tall order in an environment with a wide variety of light conditions and vehicle that may be in one of several different lanes. In addition to the cost issue, higher revolution digital cameras may result in very large file sizes. The larger the file size, the slower and more costly it is to transmit. If every image is several megabytes in size, transmission using even the expensive, high speed, TI lines may not be viable for a multi-camera system. Some digital cameras are out of service briefly while capturing an image. This cycle may not seem significant but in the case of multiple violators, it could mean that the second and third vehicles going through the red signal would not be captured by the system. With the help of a Federal Highway Administration grant there are several digital red light cameras being operated in Maryland to help answer some of the red light digital camera questions. In January 1998, Driver Safety Systems Ltd. of Israel became the first company to install a digital red light camera system in the US Peek Traffic U.K., Robot of Germany, and Redflex Traffic Systems of Australia also have initiated digital red light camera operations. Five camera systems in Howard County and one in neighboring Montgomery County transmit images automatically to a Howard County Police facility. At this facility, all images are loaded into a citation processing system built by Electronic Data Systems of Texas. Once in the citation processing system the images can be viewed under different levels of contrast and brightness to maximize the readability of the reflective registration plates that are typical in the US Using a single citation processing system helps isolate differences in the digital and wet-film cameras. A detailed description of this study is to be completed this year. Traffic Infringement Cameras in the UK Author: Lt. Glenn Hansen, commander, automated enforcement division, Howard County, Maryland, Department of Police. Date 02/00 |
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