The Chicago Police Department (CPD) uses a formula to calculate whether your neighborhood should receive a camera. If your local corner gets a score of 100, then the CPD may place a camera on the corner. The formula is:
- 1 point for calls for service
- 2 points for reported crimes (public violence, public nuisance, and drug related)
- 2 points for reported arrests (public violence, public nuisance, and drug related)
The formula relies on a 90 day period with a distance of about 200 meters from the camera location. So assuming you could get the data, here is a hypothetical analysis for 5000 W Madison:
100 Calls for Service = 100 points
20 Reported crimes = 40 points
25 Arrests = 50 points
Total = 190 points
The 190 points is above the threshold score of 100 and therefore 5000 W Madison could be a candidate for a CPD surveillance camera.
Unfortunately, the CPD doesn’t make it easy to calculate these scores. Only reported crimes is publicly available at gis.chicagopolice.org. Even then, the CPD restricts you to viewing 14 days of data at a particular location, even though they provide 90 days worth of data. The other two sources of data, calls for service and arrests, are not provided to the public by the CPD web page. Don’t get me started on the lack of crime data, it’s really an injustice!
rshah Chicago
Thanks to the work of the Tribune News App team in posting how to generate maps, I put together a map of 187 intersections with red light cameras.
Here is a link to the KML data, please let me know if anything needs to be updated.
rshah Crime, Red Light Cameras
[From L.A. Consequential - Opinionator Blog - NYTimes.com]
In a column in the NY Times, Tim Egan’s writes about the crime drop in LA. The LA murder rate is down 50% from 2 years ago. Omaha, Nebraska has a higher murder rate than LA.
Los Angeles is on a pace for about 230 murders this year, in a city of nearly 4 million people. And the department clears — solves and prosecutes — more than 80 percent of the homicides, well above the national average for big cities.
So what is the explanation for the drop in crime? As Egan notes, there are lots of possible factors:
A high-tech mapping strategy, where police move on crime hot spots in something close to real time, was pioneered in New York and mastered here (give praise to William Bratton, who oversaw the departments in both cities, for that effort); the stuffing of prisons with career criminals also gets much of the credit; the role played by legalized abortion, according to the authors Steven Levitt and Stephen Dubner in their book “Freakonomics,” in preventing a generation of unwanted children from being born; and the settling down of the drug trade, the source of so much violence during the formative years of narcotic fiefdoms, to such a degree that in many parts of the city there are now more medical marijuana dispensers in Los Angeles than Starbucks outlets (regulated retailers creating an ecosystem of nonviolence).
Interestingly, LA has accomplished this without a reliance on surveillance cameras. Unlike Chicago, where cameras are given prominence, I believe cameras play a tiny role in the LA police strategy. While this is quite anecdotal, it does pose the question of whether cameras are the most effective tool for fighting crime. LA’s successful strategy has focused on using Compstat and hiring more police officers in the last few years.
rshah Crime, Other Cities
A previous post focused on the extent of Automated License Plate Recognition (ALPR) in Chicago. It noted there were at least 75 locations (both fixed and mobile) operated by the police or OEMC that use ALPR. The post explores the effectiveness of the ALPR technology. For three different sources, here are some statistics on their effectiveness:
In the first ten months of the cameras (starting from January 2006), they had recovered 310 vehicles for the first 2.3 million plates scanned – see Sun-Times from Nov. 2006. By May 2007, there were 725 vehicles recovered and 6.5 million plates scanned. By spring 2009, there were over 13 million plates scanned and 1000 vehicles recovered. (The data also includes arrests). Here is a graph of the recovered vehicles over time:
I was a bit surprised when I saw these results (based on three data points). I would have expected a high rate of recovered cars initially and then a gradual taper to a plateau. First, I don’t have the most reliable data sources. Second, I don’t know much about the circumstances of how these cameras were deployed (how the cameras come online, how they were deployed, where they were use).
The average is one recovered car per day (using over 75 cameras). There are also 325,000 license plates scanned every month on average. If every camera is working equally, this works out to 144 license plates scanned per day with each of the 75 cameras. This is a very low number, because some of these cameras are capable of scanning 3,600 license plates per hour! I have no idea why this discrepancy exists.
I can’t fully explain this data, but I thought it would be useful to publish it. Please let me know if you have any explanations.
rshah ALPR, Chicago
[From The Wired Repo Man - He’s Not ‘As Seen on TV’ - NYTimes.com]
ALPR is moving beyond law enforcement and finding other uses. This article shows how repossession agents are using ALPR to find vehicles that are delinquent. The repo agent drives around until their ALPR finds a car that is delinquent (one rep man uses a ka-ching cash register sound for successful matches). The database of delinquent cars comes from MVTRAC, which has a national database of around 100,000 cars. The article also contains a sidebar on the potential privacy issues.
rshah ALPR
[From Spy cameras won't make us safer - CNN.com]
A good overview column on surveillance cameras by Bruce Schneier. I agree with a lot of the points he makes. There is nothing new here, but it’s a good short argument about the use of cameras to fight crime.
rshah General
Automated License Plate Recognition (ALPR) is used throughout Chicago. It’s installed in over 40 vehicles. There are also 36 fixed locations. In 17 of those, license plate recognition occurs through real-time video. This is a major development. Using video from a pod camera, it is possible to automatically scan and process a license plate. Here is a summary from an article at officer.com:
Chicago-based EyeNet Enforcement Systems offers technology that can read license plates from video captured by the POD cameras. The camera and license plate reader system is approximately $10,000, and can be used with an existing camera. Some PODs are programmed to point in the direction provided by gunshot sensors and link with EyeNet’s license plate reader system.
Tom Tarach, CEO of EyeNet, says there were challenges with the implementation. “This had never been done before, but the Chicago Police Department was determined to make it work,” Tarach says. “With a few tweaks and adjustments we found we had a working system that could scan license plates from a video stream.” Tarach adds the Chicago police now have two EyeNet readers which can easily process real-time video streams from any of the city’s wireless POD cameras.
ALPR is also installed on the street sweepers. The system photographs license plates of illegally parked vehicles that block the path of the street sweeper, and a violation notice gets sent to the vehicle’s owner. The entire operation is fully automatic, requiring no training or action from the operator. I am not sure how extensive the street sweeper program is at this time.
rshah ALPR, Chicago
[From Ex-New York Police Officials Question Crime Data Integrity - NYTimes.com]
As crime statistics have grown in importance in policing, there is always a worry that they are being massaged. There is tremendous pressure on the police to constantly reduce crime based on crime statistics. Viewers of The Wire are familiar with how crime statistics were manipulated in that show. A recent survey of New York Police Department captains and higher-ranking officers indicated some issues with manipulating crime statistics:
The retired members of the force reported that they were aware over the years of instances of “ethically inappropriate” changes to complaints of crimes in the seven categories measured by the department’s signature CompStat program, according to a summary of the results of the survey and interviews with the researchers who conducted it.
In interviews with the criminologists, other retired senior officers cited examples of what the researchers believe was a periodic practice among some precinct commanders and supervisors: checking eBay, other Web sites, catalogs or other sources to find prices for items that had been reported stolen that were lower than the value provided by the crime victim. They would then use the lower values to reduce reported grand larcenies — felony thefts valued at more than $1,000, which are recorded as index crimes under CompStat — to misdemeanors, which are not, the researchers said.
Others also said that precinct commanders or aides they dispatched sometimes went to crime scenes to persuade victims not to file complaints or to urge them to change their accounts in ways that could result in the downgrading of offenses to lesser crimes, the researchers said.
rshah Crime
ANPR is widely used in the UK. License plate recognition is an important part of the “ring of steel” around London. According to the Register, there are over 10,000 license plate cameras in the UK, which are reading 14 million plates into a national database (National ANPR Data Centre). The data, including a picture of the plate, is saved for 2 years.
A recent story in the Independent, highlighted some potential problems with relying on ANPR. The story reports that the Automatic Number Plate Recognition (ANPR) database is “at least 30 per cent inaccurate” in the UK. This has led to the wrongful arrests and car seizures. Moreover, “In 2008, 16-year-old Hayley Adamson was killed by a Northumberland police officer responding at high speed to incorrect information on the ANPR. The officer was jailed last year.”
The UK’s experience is important for the US. As ALPR gains momentum in the US, lets look for ways to use it effectively.
rshah ALPR
The city of Chicago has tested gunshot detection technology for the last few years, previous posts on this can be found here and here. The CPD tested systems from ShotSpotter, PSI (their SECURES technology was acquired by ShotSpotter in April 2009), and Safety Dynamics. According to an article in the Sun-Times in Oct 2009, the city conducted three separate tests of gunshot sensors between 2003 and 2007 in the West Side’s Harrison Police District. Only on one occasion did the detection system send a warning prior to a person calling 911 to report the shooting. As a result, the city felt the gunshot detection systems were too expensive at a cost of $200,000 a square mile.
This mixed success concurs with a similar study on the effectiveness of SECURES gunshot detection system (not ShotSpotter) released in 2008 (based on data from 2005-6).
Despite the lackluster results, the city is going forward with installing the technology in the Loop. It will cover all two square miles. The technology will allow for real time updates on shooters, while distributing this information remotely. The cost is expected to be around $400,000.
rshah Chicago, Gunshot Detection
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