Speeding is a SNAP!®
Nothing in automobile history has generated more discussion than
the enforcement of speed laws. According to a report by the National Highway Traffic
Since the earliest days of the automobile, speed has been its most
publicized (as well as its most controversial) attribute. Because the automobile moved at
a speed faster than people were accustomed to move, it was assumed that speed was the
major aspect to be curbed. Therefore in 1901, Connecticut established the world's first
automobile speed statute, limiting speeds to 12 miles per hour in cities and 15 miles per
hour in country areas (DOT, HS 807 802).
There is universal agreement that speed is a primary cause of traffic deaths.
Speed laws were also the first traffic laws to be enforced using automated photographic
equipment. Lt. William Osburn of the National City, CA police department which has used
photo-radar for over five years concludes:
Collisions are a major social and economic issue. Speed causes
collisions. If you have the ability to reduce speed on our streets and highways then the
number of collisions and injuries will be reduced. The photo-radar speed enforcement
system is designed to slow the speed of traffic and subsequently reduce the number of
collisions (Osburn 106).
Enforcement of speed does attract public attention. In a well written and
illustrated web page, Chris Longhurst (Longhurst)
has published a document called Speed Traps - What You Need to Know - v1.5. While there
are several books on the market already that deal with speeding tickets (i.e., how to
avoid them or not pay them), none are as current as Longhurst. APCO guidelines, history
and operation of photo-radar, and how to avoid traps are all covered. While some of the
information is not accurate, the existence of such detailed information on the Internet is
indicative of the publics interest of the subject.
For an excellent review of automated speed enforcement (ASE), see Blackburn and Gilbert
who provide a comprehensive overview of the industry including legal, technical, and
operational aspects of ASE and includes a list of vendors who manufacture ASE equipment.
The U.S. Department of Transportation conducted a study in 1992 titled AUTOMATED SPEED ENFORCEMENT PILOT PROJECT FOR
THE CAPITAL BELTWAY: FEASIBILITY OF photo-radar. This study covers many of the issues
- technical, public, and legal - surrounding photo enforcement.
Even some private companies are using the technology. According to the Kaiser Cement web
site, "Kaiser Cement is the first private U.S. company using
photo-radar technology on public streets to reduce traffic speed." They are
regulating their drivers as the leave the plant.
There are several systems on the market for electronically enforcing speed laws.
The most common is photo-radar, The image on the right shows a photo-radar
unit in used in Paradise
Photo radar uses a trigger that has been known since 1842
and used widely since the early 1940s: radar. RADAR is an acronym for Radio Detection
And Ranging. It has come into such common use as a word, however, that it is
no longer capitalized. Since it is the most frequently used method in speed enforcement,
we will describe it in more detail and will present some of the more standard features of
those systems and note those features which should be reviewed carefully prior to
investing in a photo-radar solution.
In general radar is used effectively worldwide to enforce speed laws. The
effectiveness of radar is well know. While photo enforcement has not been in use as long
as radar in general, it too has proven effective. The results of a study reported by the
Canadian Multidisciplinary Road Safety Conference VII (422) is typical. It concluded that:
The evidence suggests that the radar camera program contributed to the
consistent and significant reduction of speeds and percentage of vehicles exceeding the
speed limit for southbound traffic on Knight St. compared to Granville St.
(Proceedings of the
Canadian Multidisciplinary Road Safety Conference VII 429).
Not everyone agrees, "Loveland Chief of Police Tom Wagoner says he decided
against using photo-radar for some of the same reasons. 'It's just not our style,' says
Wagoner. 'We want our officers to have a personal relationship with our citizens, and I
think that if people started receiving tickets in the mail, it would be perceived as some
sort of fund-raiser." --Loveland police chief Tom Wagoner as quoted by Tony Perez-Giese
in Westword newspapers .
In 1842, Christian Johann Doppler predicted that a relationship existed
between the frequency of received electromagnetic waves and the motion of the source of
those waves. The Doppler effect as it is known today was quantified by
Einstein and Schrödinger and is today the basis for Radar According to Skolnik:
Radar is an electromagnetic system for the detection and location of
objects. It operates by transmitting a particular type of waveform, a pulse-modulated sine
wave for example, and detects the nature of the echo signal. (Skolnik)
The Doppler Effect, stated simply, says that transmitted energy
reflected off an object will be changed in frequency in direct proportion to the relative
motion between the transmitter and reflecting object.
If the energy source and the reflecting object are moving toward each
other, the reflected frequency will be higher.
If the energy source and the reflecting object are moving away from each
other, the reflected frequency will be lower.
The basic method of radar speed measurement is:
- Radar device sends out radio signal
- Signal strikes a solid object, e.g. an automobile, and is reflected (bounced)
back towards the radar receiver.
- If there is a relative motion between the object and the radar transmitter, the
reflected signal will be different from the transmitted signal in frequency
- The amount of difference (frequency or Doppler shift) indicates the speed of the
- On the X-band, for every 1 mph difference in speed there is a 31.4Hz difference
On the K band, for every 1 mph difference in speed there is a 72.0Hz difference
in frequency .
Radar is usually known by letter-band nomenclature, e.g., k-band. Photo radar is
unlike traditional hand-held radar in two important respects, all of which increase its
accuracy and make it almost impossible for violators to detect the beam before their
violation has been registered. These differences are its low output, which at maximum
strength is only twenty-five milliwatts, and its cross-the-road beam, rather than the
traditional hand-held down-the-road beam.
The accuracy of the unit is greatly enhanced by these two differences, the low
output and the beam direction. The photo-radar unit beam cuts across the road, and can
thus detect the vehicle exceeding the set speed limit at a closer range to the patrol
vehicle. Furthermore, with a maximum output of only twenty-five milliwatts, the farthest
an object's velocity has been measured is across 5 lanes of highway. These two differences
also result in making the radar beam almost impossible for radar detectors to identify
until they have already been recorded by the unit.
Photo radar systems usually operate on the K-band at 24.15GHz. This is important
because this is designated by the FCC as one of only two bandwidths permanently assigned
for use by police radar.
As a car passes through the beam emitted by the radar antenna, the radar antenna
makes a series of measurements of the vehicle's speed. Upon identification of a speeder
from these measurements a signal is sent to the central processing unit, which in turn
directs the high speed camera to take a photograph of the violator.
Radar units by their nature are sophisticated instrumentation. As such great
care is given to the accuracy of various products prior to being put into public use. This
is usually by a method called type certification. Several agencies throughout the world
specify the requirements for and actually test radar units prior to allowing the sale. The
Organization Internationale de Métrologie Légale (OIML), the Nederlands Meetinstituut
(NMI) and the British Home Office are three such organizations.
Upon determining that a violator has been identified, the units internal
computer calculates the timing delay for the second camera, based on the speed of the
offending vehicle, the length of the patrol car, and the angle of the cameras. The second
camera, which is aimed out the front window of the photo-radar vehicle, then takes a
photograph. This second image captures the rear of the offending vehicle as it drives away
from the unit. This photograph is used to identify the vehicle when no front plate is
visible on the first photograph. As with the first photograph, this second violation
photograph contains encrypted data pertaining to the time, date and speed of the
Cameras used in photo-radar are usually high-speed, industrial cameras. Unlike
other cameras, Photo radar cameras are designed for traffic enforcement photography. A
high speed flash system is integrated into the photographic unit, allowing for enforcement
on a 24-hour basis. The flash unit is usually synchronized at 1/1000 of a second, and is
used for both day and night deployments. The flash bulb is sealed within a water-resistant
housing, and is located on the outside of the unit. The high-speed of the flash, combined
with its low light output, allows for the units safe operation during both day and night
Photo radar systems are composed of three main subsystems:
- Radar emission and detection,
- Camera, and
Radar Emission and Detection
Fundamental to the operation of a photo-radar system is the emission of a
microwave beam and the detection of the reflected signal.
As a car passes through the beam emitted by the radar antenna, the unit
additionally undergoes a self-test to verify its accuracy. If it is not operating
properly, then the unit automatically enters standby mode. If the self-check is
successfully completed, the radar antenna takes a series of measurements of the vehicle's
speed. These figures are then averaged, and if any deviates from the mean by more than 2%
the photograph is not taken. Always giving the driver the benefit of the doubt, the radar
antenna takes additional measurements of the speeding car passing through its beam. These
measurements are then compared to the average speed calculated from the first set of
measurements. If any of these deviate, then the vehicle is not photographed.
The system may also come equipped with an internal or external Tuning Fork which is used to independently check the vibration at
the beginning and end of each deployment. Since standard tuning forks do not create a
histogram similar to that created by a vehicle, software capable of distinguishing between
actual and simulated vehicle Doppler radar readings must often be employed. This error
prevention algorithm must be designed to prevent common mis-reads created by objects found
in the urban environment, such as the vibration of electrical substations.
Radar Beam Angle, Width, and Power
Radar antennas emit beams at specific angles and specific power levels depending
on the vendor. Using an appropriate angle and low power ensure that radar detectors are
incapable of detecting the photo-radar until they are in the beam and an accurate speed
measurement has already been determined. A 5° beam width and an antenna measuring angle
of 20° are typical and allows for accurate speed measurements of vehicles on roadways
from 1 to 5 lanes in width.
Since it is impractical to place a photo-radar unit in same vector as the
vehicle being measured, a correction must be made to account for any displacement. A
normal deployment frequently set the radar at a 20° angle relative to the direction of
travel. The technique for calculating the correction is called the cosine effect.
The cosine effect is used to determine the actual speed of a vehicle given the
indicated speed and the angle of the beam. This relationship is expressed as: True
Speed = Indicated Speed/Cosine q
The radar antenna and radar control unit (CU) are usually powered by an
independent battery pack, which contains a minimum of two 26Ah 12V DC sealed lead acid
marine type batteries capable of supplying all required power for a full days
operation, and a 110V AC recharging system. The radar antenna and CU can not be operated
while the 110V AC recharging system is supplying the battery. This technique complies with
all case law requirements regarding a separate power supply for the radar antenna and RDU.
These components should not be connected in any way to the vehicles battery
The cameras used in photo-radar systems
are high speed industrial cameras. Cameras used in photo-radar system are specifically
designed for traffic enforcement photography. The front facing cameras usual 90 mm
lens is designed for capturing the characters on rear license plates. This is of great
importance because the lens is the critical ingredient in the quality of the photograph.
Picture quality is a function of camera type - digital (KODAK digital image shown at left)
or wet film. If wet film, lens length and quality, negative size, film type and processing
will impact quality.
Second Camera for Rear Photography
An additional camera is frequently used to photograph the rear of the violating
vehicle as it passes the photo-radar unit. A rear facing cameras typical 150 mm lens
is designed for photographing both the driver's face and the front license plate at a wide
range of speeds and lighting conditions. The second photo is coordinated with the first.
Once a violator is identified, a units internal computer can calculate the timing
delay for the second camera, based on the speed of the offending vehicle, the length of
the patrol car, and the angle of the cameras. The second camera, which is usually aimed
out the front window of the police vehicle, then takes a photograph. This second image
captures the rear of the offending vehicle as it drives away from the unit. This
photograph is used to identify the vehicle when no front plate is visible on the first
Each photograph (front and rear) may contain the following:
- Scene of location where violation occurred.
- Motor vehicle during violation.
- Clear display of drivers face (frontal photograph only).
- Day, month and year of the violation.
- Hour, minute and second of the violation.
- Speed of the vehicle in miles per hour.
- Operator identification number.
- Location of violation.
- Speed limit at location
- Only the violations vehicle in the photograph.
- Frame sequence number.
- The data is positioned so as not to obstruct the violation photograph.
A flash tube and optimized lamp reflector is usually required to properly
illuminate a vehicle. It must be capable of providing adequate illumination under all
light and weather conditions, including:
- Up to four lanes in one direction
- Varying levels of ambient light conditions from full sunlight to no external
The flash system must also be safe for passing motorists. Many citizens are
concerned about frontal flash and may claim that it is unsafe to expose a driver to such a
bright light. In reality the flash is intense but of very short duration. It is much less
distracting than lightning and there are no cases of recorded accidents resulting from
flash units used in photo enforcement. In some cases red filters are used over the flash
units to reduce the affect but these are most frequently used with black and white film
since they produce poor color images.
Flash intensity is as critical with photo-radar as it is with other forms of
photo enforcement. The lower position of the flash as well as the relative close proximity
of the vehicle being photographed aids in obtaining quality photographs. Lighting the
interior of a vehicle for purposes of driver identification for those jurisdictions
requiring it is equally a problem, however. Cameras are usually pre-adjusted to provide
optimum light under the widest range of conditions. However, in the event that an
adjustment is required, flash settings can usually be selected on site.
Photograph Rate and Volume
Cameras able to take in excess of two photographs per second are usually used in
photo-radar systems. Such cameras are also able to take many thousands of photographs
before needing servicing. These cameras far exceed the durability specifications for
standard professional 35MM cameras usually seen by professional photographers. Such
reliability is very important for high-volume purposes such as traffic photography.
Photo radar cameras are usually completely automated. This includes automatic
camera activation controlled by the radar antenna. The cameras are manually or
automatically leveled and pre-aligned with the radar antenna. The film can easily be
loaded and unloaded, and any length of film from a standard 36 frame roll to a
professional 100 ft. (800 frames) roll can usually be used with the cameras.
Some method of entering deployment
information and setting and testing the system must be provided. This may be done using a
simple control panel or through the use of a more elaborate graphic user interface running
on a PC such as the ATS unit shown at left..
Units should be certified by independent laboratories to provide accurate speed
measurements ranging from 15 to 150 m.p.h.
Agencies in more than forty countries worldwide use systems year-round in
densely urban, suburban and rural environments and under all types of weather conditions.
A system must have been tested and certified to operate at the widest temperate range of
any photo-radar system in the world, 22°F to 140°F (-30°C to +60°C).
Two calibration tests should always be conducted to ensure system accuracy. The
first is an internal calibration test which tests for speed measurement accuracy, the
results of which are recorded on a photograph which includes a special test indication. A
failure results in the system being unable to continue normal operation. The test provides
a visible indication on the systems LCD displays, and the nature of any failure is
A video system capable of recording all vehicles passing though the site is
often desired by jurisdictions.
Most photo-radar systems used today are generally
deployed as stationary units. However, the technology exists to have mobile units record
violations on film. Currently this is across-the-road, opposite direction detection with
only one photo being made. The trend in radar development is for same direction, front or
rear detection. In the near future photo systems should take advantage of this development
and products allowing for moving radar will be more common.
Operation of a Photo Radar system
Photo radar units can be mounted for fixed or mobile deployments. When the units
are mounted for mobile use they are usually either mounted inside a specially equipped
vehicle or on a tripod .
A Minivan is often selected for mobile deployment due to its advanced safety
features and higher degree of vehicle reliability. A vehicle selected for photo
enforcement frequently has the following characteristics:
- 6-8 cylinder engine
- Power steering and brakes.
- Dual outside mirrors.
- AM/FM radio.
- Air conditioning.
- Automatic transmission.
- Step rear bumper.
- Class I tow hitch and wiring which meets jurisdictions standards
If a jurisdiction desires, most photo-radar systems can be mounted on a tripod
as well as in the rear of a specially modified vehicle.
Detecting and Displaying Speed
If, as in most cases, the vehicle's measurements remain constant, the time,
date, speed and other relevant information are then displayed on an LED panel in the
camera base and a photograph is taken of the front of the vehicle.
Measuring Approaching and Receding Traffic
Systems are available which measure speeds of both approaching and receding
Mobile Roadside Display Board
A large display board mounted on the rear
of the operating unit and providing an indication of the passing vehicles speed is
available from most vendors. The digits are usually 9-10 inches in height and displayed in
a florescent yellow color for night-time visibility. At the operators option (and in
accordance with a jurisdictions policy), the speed display can be set to display the
speeds of all passing vehicles, or only those of violators.
A more sophisticated display is produced by Computer Recognition Systems, In.
Called SVDD, Speed Violation Detection Deterrent
According to CRS:
Excessive speed contributes to a substantial proportion of accidents. It increases the
likelihood of death and the severity of personal injury. In recent years there has been
many efforts to curb the speed limit through work zones on the highway, but compliance is
poor and accident potential remains high. More effective ways of controlling speed was
necessary. To respond to this need SVDD was developed by Computer Recognition Systems Ltd.
in conjunction with Travers Morgan Ltd.
SVDD - Speed Violation Detection/Deterrent - is a real-time application of computerized
image recognition to read numberplates in order to measure speeds of vehicles as they
enter a restricted speed work site. Immediate notification of the violation using a
downstream variable message sign creates a controlled speed environment which should deter
fliture speeding. The emphasis is upon deterring speed limit violation by constant
demonstration of automatic monitoring.
SVDD deploys cameras at either end of a measured base line to observe traffic flow within
the initial length of a 50 mph restricted roadworks site. It operates 24 hours a day. The
image recognition system reads registration plates and records the time of observation. By
matching the observations at either end of the base line, the average speed is calculated.
Details of vehicles violating the specified speeding threshold are recorded for subsequent
prosecution, if necessary. The deterrent effect of SVDD is generated by the immediate
illumination of the VMS showing the registration plate and the speed the errant motorist.
On subsequent passage through the site, the motorist will be expected to moderate his
speed at the 'Automatic Speed Monitoring' advance warning sigh erected in coljuncti6n with
the 50 mph warning signs.
THE BIGGER PICTURE
SVDD at major roadworks is an initial application providing real-time traffic information
from automatic number
plate reading. The technoloogy is now available fordevelopment of traffic management and
network optimization systems of tomorrow. Its capabilities as a vehicle traffic system are
also suitable for:
- Permanent speed limit enforcement
- Speed/flow optimization on congested roads
- Journey time monitoring
- Incident detection and delay advice
- Wide network journey time advice
- Overweight vehicle identification
- Illegal lane use detection
- HOV lane detection
Summary of Formulae Relating to Radar
- Speed From Doppler Frequency
- For X-Band S=Doppler Shift (in C.P.S) / 31.4
- For K-Band S=Doppler Shift (in C.P.S) / 72.0
- Beam Width
- Width = Z (TAN q 1/2) * Distance
- Stationary Cosine
- True Speed = Indicated Speed / Cosine q
- Indicated Speed = True Speed * Cosine q
- Moving radar Speed Computation
- Target Speed = Combined Speed - Patrol Speed
- Mobile Cosine
- (True Combined Speed) * Cosine q - (True Ground Speed) * Cosine q =
(Indicated Target Speed)
- Distance Calibration - Stationary Operation
- Distance = Speed of Target * 1.47 * Time Clocked (sec.)
- Distance Calculation - Mobile Operation
- Distance = Combined Speed * 1.47 * Time Clocked (sec.)
While RADAR is
the most popular trigger used in the photo enforcement of speed laws, there are other
effective methods as well. An Israeli company, Driver Safety Systems (DSS) manufacturers a product called the MAROM
System which uses reflected light as a trigger. According to DSS,
- "DSS's electro-optic technology has significant advantages over traditional
enforcement technologies, such as a radar. The DSS technology can be neither detected nor
jammed, is not subject to interference, and has no "field-of-view" problems when
two vehicles are next to each other...Among the tasks MAROM performs are:
- Automatically measures the speed of every passing vehicle in a given traffic
lane, with unsurpassed accuracy.
- Measures time between vehicles traveling in a given lane -- Providing proof of
- Captures video images of all vehicles exceeding pre-set speed and/or tailgating
- Distinguishes specific classes of vehicles by length.
- Retains all of the above data on Digital Audio Tape (D.A.T.) for statistical and
- Produces printed reports or notices, complete with a photograph of the actual
license plate number."
What is Photo-LIDAR?
According to Ingram Technology:
Photo-LIDAR is the new generation replacement for the
older Photo-Radar systems. LIDAR uses an IR Pulsed Laser Diode to measure speed, distance
and direction. By using beam width of less than one-degree, an accuracy level is achieved
that can not be reached by the older radar systems. As the beam crosses the traffic lanes,
it can only target one vehicle at a time and minimize the possibility of false readings.
The beam can also be "gated" so that only vehicles within a set of distances
will be read. The other feature of LIDAR is that a vehicle traveling in only one direction
can be captured by the system, if desired.
In the Auto-Trax
Photo-LIDAR system, the unit is mounted in parallel with a high-definition digital
video camera and a mobile computer system. Photo's are taken of both the front (face) and
rear (plate) of the vehicle in violation. Non violating vehicles are also counted and
timed for demographic purposes only. The unit is fully digital and uses no film or tape.
US Photo Radar Media Articles
Central 95-02-06: American Traffic Systems: "Road looks smooth
for Scottsdale firm" talks about BC program
Evergreen Times [San
Jose, CA]: 96-03 "City hopes photo-radar system will make drivers slow
Collins, Colorado] This Week 96-08-08: "Smile, You're On Camera"
Denver 97-08-29 "Cops and cameras a match made in hell"
News Times 96-06-13: "Hard Driving"
Salt Lake [Utah] Tribune 96-04-29: "Photocop's Shutter Snaps on it's Final
San Francisco Chronicle 97-01-27: "Reprieve for Speeders Caught on
97-10-13 "America's fast lane: Montana"
Washington Post 97-11-06 "Why Speed Doesn't Always Kill"
The Washington Times
Willow Glen Resident [San Jose, CA]
BC's Photo Radar Program Media Articles
Neighborhood Traffic Management is a strategy new to North
America. It has been practiced in Europe, the United Kingdom, and Australia for many
years. The methodology is to influence driver behavior by psychological, or visual means
Clark County (WA) Neighborhood Traffic Program is using photo-radar as
part of their neighborhood traffic management program to monitor school zones.