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Chapter 1
Introduction
While driving on highways, motorists should not exceed the maximum speed limit
permitted for their vehicle. However, accidents keep occurring due to speed violations
since the drivers tend to ignore their speedometers.
This speed checker will come handy for the highway traffic police as it will not only
provide a digital display in accordance with a vehicle’s speed but sound an alarm if the
vehicle exceeds the permissible speed for the highway.
The system basically comprises two laser transmitter-LDR sensor pairs, which are
installed on the highway 100 meters apart, with the transmitter and the LDR sensor of
each pair on the opposite sides of the road. The installation of lasers and LDRs is shown
fig below. The system displays the time taken by the vehicle in crossing this 100m
distance from one pair to the other with a resolution of 0.01 second from which the speed
of the vehicle can be calculated as follows:
Speed (kmph) = Distance/Time
= 0.1 km
(Reading x 0.01)/3600
Or, Reading (on display) =36000/Speed
Figure 1 –Installations of lasers and LDR`S on highways
As per the above equation for a speed of 40 kmph the display will read 900 (or 9 second),
and for a speed 60 kmph the display will read 600 (or 6 seconds). Note that the LSB of
the display equals 0.01 second and each succeeding digit is tem times the preceding digit.
You can similarly calculate the other readings (or time).
Chapter 2
Circuit Description
This circuit has been designed assuming that the maximum permissible speed for
highways is either 40 kmph or 60 kmph as per the traffic rule.
The circuit is built around five NE555 timer ICs (IC1 through IC5), four Cd4026 counter
ICs (IC6 through IC9) and four 7-segmint displays (DIS1 through DIS4). IC1 through
IC3 function as monostables with IC1 serving as count –start mono, IC2 as count –stop
mono and IC3 as speed-limit detector mono, controlled by IC1 and IC2 outputs. Bistable
set-reset IC4 is also controlled by the outputs of IC1 and IC2 and it (IC4), in turn controls
switching on/off of the 100Hz (period=0.01 second) astable IC5
The time period of timer NEE555 (IC1) count –start monostables multivibrator is
adjusted using preset VR1 or VR2 and capacitor C1.For 40kmph limit the period is set
for 9 seconds using preset VR1, while for 60kmph limit the time period is set for 6
seconds using preset VR2 .Slide switch S1 is used to select the time period as per the
speed limit (40 kmph and 60 kmph, respectively). The kmph and 60 kmph,
respectively) .The junction of LDR1 and resistor R1 is coupled to pin 2 of IC1.
Normally, light from the laser keeps falling on the LDR sensor continuously and thus the
LDR offers a low resistance and pin 2 of IC1 is high. Whenever light falling on LDR is
interrupted by any vehicle, the LDR resistance goes high and hence pin 2 of IC1 goes
low to trigger the monostables .As a result, output pin 3 goes high for the preset period (9
or 6 seconds) and LED1 glows to indicate it. Reset pin4 is controlled by the output of
NAND gate N3 at power or whenever reset switch S2 is pushed.
For IC2, the monostables is triggered in the same way as IC1 when the vehicle intersects
the laser beam incident on LDR2 to generate a small pulse for stopping the count and for
use in the speed detection.LED2 glows for the duration for which pin 3 of IC2 is high.
The outputs of IC1 and IC2 are fed to input pins 2 and 1 of NAND gate N1, respectively.
When the outputs of IC1 and IC2 go high simultaneously (meaning that the vehicle has
crossed the preset speed limit), output pin 3 of gate N1 goes low to trigger monostables
timer IC3. The output of IC3 is used for driving piezobuzzer PZ1, which alerts the
operator of speed –limit violation .Resistance R9 and capacitor C5 decide the timer
period for which the piezobuzzer sounds.
The output of IC1 triggers the bistable (IC4) through gate N2 at the leading edge of the
count-start pulse. When pin 2 of IC4 goes low, the high output at pin 3 enables clock
generator IC5, since the count-stop pulse output of IC2 is connected to pin 6 of IC4 via
diode D1, it resets clock generator IC5. IC5 can also be reset via diode D2 at power-on as
well as when reset switch S2 is pressed.
IC5 is configured as an astable multivibrator whose time period is decided by preset
VR3, resistor R12 and capacitor C10. Using preset VR1, the frequency of astable
multivibrator is set as 100 Hz. The output of IC5 is fed to clock pin 1 of decade
counter/7-segment decoder IC6 CD4026.IC CD4026 is a 5-stage Johnson decade counter
and an output decoder that converts the Johnson code into a 7-segment decoded output
for driving DIS1 display. The counter advances by one count at the positive clock signal
transition.
The carry–out (Count) signal from CD4026 provides one clock after every ten clock
inputs to clock the succeeding decade counter in a multidecade counting chain. This is
achieved by connecting pin 5 of each CD4026 to pin of the next CD4026.
A high reset signal clears the decade counter to its zero count. Pressing switch S2
provides a reset signal to pin 15 of all CD4025 ICs also IC1 and IC4. Capacitor C12 and
resistor R14 generate the power-on-reset signal
The seven decoded outputs ‘a’ through ‘g’ of CD4026 illuminate the proper segment of
the 7-segment displays (DIS1 through DIS4) used for representing the decimal digits ‘0’
through ‘9’ .Resistor R16 through R19 limit the current across DIS1 through DIS4,
respectively.
Figure 2 –Circuit of power supply
Fig. above shows the circuit of the power supply. The AC main is stepped down by
transformer X1 to deliver the secondary output of 15 volts, 500 mA. The transformer
output is rectified by a bridge rectifier comprising diodes D3 through D6, filtered by
capacitor C15 bypass regulated 12V supply. Capacitor C15 bypasses any ripple in the
regulated output. Switch S3 is used as the ‘on’/’off’ switch. In mobile application of the
circuit, where mains 230V AC is not available, it is advisable to use an external 12V
battery .For activating the lasers used in conjunction with LDR1 and LDR2, separate
batteries may be used.
Chapter 3
Construction and Working
Assemble the circuit on a PCB. Before operation, using a multimeter check whether the
power supply output is correct, if yes apply power supply to the circuit by flipping switch
S3 to ‘on’. In the circuit, use long wires for connecting the two LDRs, so that you can
take them out of the PCB and install on one side of the highway, 100 meters apart. Install
the two laser transmitters (such as laser torches) on the other side of the highway exactly
opposite to the LDRs such that laser light falls directly on the LDRs. Resets the circuit by
pressing switch S2, so the display on the LDRs. Resets the circuit by pressing switch S2,
so the display shows ‘0000’. Using switch S1, select the speed limit (say, 60 kmph) for
the highway.
When any vehicle crosses the first laser light, LDR1 will trigger IC1. The output of IC1
goes high for the time set cross 100 meters with the selected speed (60 kmph) and LED1
glows during for period. When the vehicle crosses the second laser light, the output of
IC2 goes high and LED2 glows for this period.
Piezobuzzer PZ1 sounds an alarm if the vehicle crosses the distance between the laser
set-ups at more than the selected speed (lesser period than preset period). The counter
starts counting when the first laser beam is intercepted and stops when the second laser
beam is intercepted. The time taken by vehicle to cross both the laser beams is displayed
on the 7-segment display. For 60 kmph speed setting, with timer frequency set at 100 Hz,
if the display count is less than ‘600’. It means that the vehicle has crossed the speed
limit (and simultaneously the buzzer sounds). Reset the circuit for monitoring the speed
of the next vehicle.
Chapter 4
Precautions
To make sure that ambient light dose not falls on LDRs, house the LDRs is black tube
pointing to wards the light sources. The ICs should be soldered carefully. It is better to
use IC bases and plug in the ICs later. The solder to IC pin should not be dry or loose.
Chapter 5
Components
5.1 LDR :
Electronic optosensors are devices that alter their electrical characteristics, in the
presence of visible or invisible light. The best-known devices of these types are the LDR
(light dependent resistor), the photodiode, and the phototransistor
LDR operation relies on the fact that the conductive resistance of a film of cadmium
sulphide (Cds) varies with the intensity of light falling on the face of the film. This
resistance is very high under dark conditions and low under bright conditions.
The device consists of a pair of metal film contacts separated by a snake-like track of
cadmium sulphide film, designed to provide the maximum possible contact area with the
two metal films. The structure is housed in a clear plastic or resin case, to provide free
access to external light.
LDRs are sensitive, inexpensive, and readily available devices. They have good power
and voltage handling capabilities, similar to those of a conventional resistor. Their only
significant defect is that they are fairly slow acting, taking tens or hundreds of
milliseconds to respond to sudden changes in light level. Useful practical LDR
applications include light- and dark- activated switches and alarms, light beam alarms,
and reflective smoke alarms etc.
5.2 Variable resistance :
Variable resisters are those resisters in which resistance value can be varied, with in a pre
determined range. These are three terminal devices. Two terminals are fixed while the
third one is connected to a moveable tap which slides along the resistive element,
changing the resistance between ends tap terminal
Variable resistance are also called as potentiometer
5.3 PCB :
A printed circuit board properly known as PCB is a piece of plastic electronic circuit
consisting of copper or special photo engraving process prints silver –conducting path.
On the other side of the PCB electric components are mounted like resistors, capacitors,
diodes, transistors, transformers, tubes, and IC’s. Suitable holes are punched in the PCB
for mounting the components, which are connected to the conducting paths by soldering.
5.4 LED :
A light-emitting diode (LED) is a semiconductor device that emits incoherent
monochromatic light when electrically biased in the forward direction. The color of the
emitted light depends on the chemical composition of the semiconducting material used,
and can be near-ultraviolet, visible or infrared.
5.5 Resistors :
The circuit elements which offers an opposition to electric current flowing in a circuit is
known as resister and its value of resistance is expressed in ohms. The Ohm is denoted by
Greek letter Omega ().
5.6 Capacitors :
The capacitors are the most widely used passive element next to resistors. Capacitor is
made up of two parallel plates separated by insulating materials called as dielectric.
Capacitance is defined as the ability of capacitor to store charge.
5.7 Push to ON Switch :
They are used for makes the connection only when switch is pressed. On releasing button
the connection must be break down.
5.8 IC Base :
They are for mounting of IC’s on PCB i.e. they help us to remove or put IC’s on PCB
with very easy push or pull action. They are available according to the numbers of pins of
IC’s used.
5.9 Seven segment LED Display :
LTS543 is common cathode 7- segment LED display. These display devices are used in
application where the viewer is within 6 m of display. This type of LED fits into standard
dip sockets with 1.52 cm pin rows it also has a decimal point on the lower right hand
side.
5.10 NE 555 :
Description
The NE555 is a highly stable controller capable of producing accurate timing pulses.
With a monostable operation, the time delay is controlled by one external resistor and one
capacitor. With an astable operation, the frequency and duty cycle are accurately
controlled by two external resistors and one capacitor
Features :
• High Current Drive Capability (200mA)
• Adjustable Duty Cycle
• Temperature Stability of 0.005%/°C
• Timing From µSec to Hours
• Turn off Time Less Than 2µSec
Internal Block Diagram
Figure 3- Internal diagram
Application Information :
Monostable Operation :
Figure 4 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse
whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to
the #2 pin falls
below Vcc/3 while the
timer output is low, the
timer's internal flip-
flop turns the
discharging Tr. off and
causes the timer
output to become
high by charging the
external capacitor C1
and setting the flip-
flop output at the
same time.
Figure 4-
Monostable circuit
The voltage across the external capacitor C1, VC1 increases exponentially with the time
constant t=RA*C and reaches 2Vcc/3 at td=1.1RA*C.
Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC,
the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant R AC
controls the output pulse width.
When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the
trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C1
begins to discharge and the timer output converts to low.
In this way, the timer operating in the monostable repeats the above process. Figure 2
shows the time constant relationship based on RA and C.
It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a
minimum of Vcc/3 before the timer output turns low. That is, although the output remains
unaffected even if a different trigger pulse is applied while the output is high, it may be
affected and the waveform does not operate properly if the trigger pulse voltage at the
end of the output pulse remains at below Vcc/3.
Astable Operation :
In the astable operation, the trigger terminal and the threshold terminal are connected so
that a self-trigger is formed, operating as a multi vibrator. When the timer output is high,
its internal discharging Tr. turns off and the VC1 increases by exponential function with
the time constant (RA + RB) x C. When the VC1, or the threshold voltage, reaches 2Vcc/3,
the comparator
output on the trigger
terminal becomes
high, resetting the
F/F and causing the
timer output to
become low. This in
turn turns on the
discharging Tr. and
the C1 discharges
through the
discharging channel
formed by RB and the
discharging Tr. .
Figure 5-Astable circuit
When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes
high and the timer output becomes high again. The discharging Tr. turns off and the V C1
rises again. In the above process, the section where the timer output is high is the time it
takes for the VC1 to rise from Vcc/3 to 2Vcc/3, and the section where the timer output is
low is the time it takes for the VC1 to drop from 2Vcc/3 to Vcc/3.
The explanations of terminals coming out of the timer IC is as follows:
Pin 1: Ground terminal: It is a common ground terminal. All the voltages measured
with respect to this terminal.
Pin 2: Trigger terminal: This pin is an inverting input to comparator, which is
responsible for transition of flip flop from set to reset. The output stage of timer depends
on the amplitude on external trigger pulses applied to this pin.
Pin 3: Out put terminal: Output of timer is available as this pin. Normally its level
remains low and only during timing interval it goes high. There are two ways to connect
the load to this terminal .One is to connect the load between pin-3 and pin-8, which is
called floating supply load. Since in the case of floating supply load, current only flows
during low state of output and during high state of output and during high state of output,
there is on current i.e. when output is off, load current is on, therefore floating supply
load is also known as “normally on load”, Science in case of floating supply load, load
current flows through load into output terminal therefore this current is known as sink
current while in case of grounded load, load current flows of output terminal. Therefore it
is called source current.
Pin 4: Reset terminal: To disable or reset the timer a negative pulse is applied at this pin
due to which it is called reset terminal.
Pin 5: Control voltage terminal: Function of the control voltage terminal is to control
the threshold and trigger level and that is why this terminal is called control
terminal .This either the external voltage or a potentiometer connected at this pin can also
be used to modulate the output waveform. When this pin is not used for the above
purpose, it should be connect to ground through a 0.01 microfarad capacitor to bypass
noise and ripple voltage from the power supply so as to minimize their effect on
threshold voltage.
Pin 6: Threshold terminal: It is a non –inverting terminal of comparator, which
compares the voltage applied at this terminal with a reference voltage of 2Vcc/3. Thus
the amplitude of the voltage at threshold terminal is responsible for the set of flip flop.
Pin 7: Discharge terminal : At this pin ,collector of a transistor is connected internally
and mostly a capacitor is connected externally between this terminal and ground .It is
called as discharge terminal because when a transistor saturates , capacitor discharges
through the transistor is in cutoff, the capacitor charges at a rate of determined by the
external resistor and capacitor.
Pin 8: Supply terminal: A supply voltage Vcc of +5 V is applied to this pin with respect
to ground. Due to such a large range of Vcc from +5 V existing digital logic supplier,
linear IC supplies and automatic on dry cell batteries can power 555.
IC 555 timer finds very useful application in many other projects such as:
Precision timing, sequential timing.
Pulse shaping.
Pulse generator.
Missing pulse generator.
Time delay generator.
Frequency division.
Traffic light control.
Infrared remote control timer.
5.11 Diode 1N4148 (Small-Signal Diode) And 1N4007 :
Diode 4148 performs switching operation here. Whenever the logical level at their anode
is 1 they switch on and provide a positive pulse to the circuit connected to them. Diode
4007 is a rectifying diode used in bridge rectifier.
5.12 IC 7812 3-Terminal 1A Positive Voltage Regulator :
Description
The LM7812 three terminal positive regulators are available in the TO-220/D-PAK
package and with several fixed output voltages, making them useful in a wide range of
applications. Each type employs internal current limiting, thermal shut down and safe
operating area protection, making it essentially indestructible. If adequate heat sinking is
provided, they can deliver over 1A output current. Although designed primarily as fixed
voltage regulators, these devices can be used with external components to obtain
adjustable voltages and currents.
Features :
• Output Current up to 1A
• Output Voltages of 12V
• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection
Internal Block Diagram :
Figure 5- Internal block diagram of IC 7812
5.13 IC CD4011 Quad 2-Input NAND Buffered B Series Gate :
General Description
The CD4011BC quad gates are monolithic complementary MOS (CMOS) integrated
circuits constructed with N- and P-channel enhancement mode transistors. They have
equal source and sink current capabilities and conform to standard B series output drive.
The devices also have buffered outputs which improve transfer characteristics by
providing very high gain. All inputs are protected against static discharge with diodes to
VDD and VSS.
Features
Low power TTL
5V–10V–15V parametric ratings
Symmetrical output characteristics
Max input leakage 1A at 15V over full temperature. range
Connection Diagrams
Figure 6-Connection diagram of IC CD4011
5.14 IC CD4026 :
CD 4026 consist of a 5-stage Johnson decade
counter and an output decoder which converts the
Johnson code to a 7-segment decode output for
driving one stage in a numerical display.
These devices are particularly advantageous in
display applications where low power dissipation
and/or low package counts are important.
Input is CLOCK INHIBIT, common outputs are
CARRY OUT and the seven decoded outputs (a, b, c, d,
e, f, g). Additional inputs and outputs for the CD 4026
include DISPLAY ENABLE input and DISPLAY ENABLE and UNGATED "C-
SEGMENT" outputs.
A high RESET signal clears the decade counter to its zero count. The counter is advanced
one count at the positive clock signal transition if the CLOCK INHIBIT signal is low.
Counter advancement via the clock line is inhibited when the CLOCK INHIBIT signal is
high. The CLOCK INHIBIT signal can be used as a negative-edge clock if the clock line
is held high. Antilock gating is provided on the JOHNSON counter, thus assuring proper
counting sequence. The CARRY-OUT (Cout) signal completes. The cycle every ten
CLOCK INPUT cycles and it is used to clock the succeeding decade directly in a multi-
decade counting chain. The seven decoded outputs (a, b, c, d, e, f, g) illuminate the
proper segments in a seven segment display device used for representing the decimal
numbers 0 to 9. The 7-segment outputs go high only when the DISPLAY ENABLE IN is
high.
Chapter 6
List of components
Semiconductors:
IC1-IC5 NE555 timer
IC6-IC9 CD4026 decade counter/7segment decoder
IC10-CD4011 NAND gate
IC11 7812 12 V regulator
D1, D2 1N4148 switching diode
D3-D6 1N4007 rectifier diode
LED1 Green LED
LED2, LED3 Red LED
DIS1-DIS4 LTS543 common-cathode, 7 segment display
Resistors:
R1, R4 100-kilo-ohm
R2, R5, R6, R8,
R10, R11, R14 10-kilo-ohm
R3, R7, R13, R16-R19 470-ohm
R9 470-kilo-ohm
R12, R15 1-kilo-ohm
VR1, VR2 100-kilo-ohm preset
VR3 20-kilo-ohm preset
Capacitors:
C1 100µF, 25v electrolytic
C2, C4, C6
C8, C11 0.01µF ceramic disk
C3, C13, C15 0.1µF ceramic disk
C5 10µF, 25v electrolytic
C7 0.47µF, 25v electrolytic
C9 0.2µF ceramic disk
C10 1µF, 25v electrolytic
C12 47µF, 25v electrolytic
C14 1000µF, 35v electrolytic
Miscellaneous:
X1 230V AC primary to 0-15V, 500mA secondary
transformer
PZ1 Piezobuzzer
LDR1, LDR2 Light Dependent Resistors
S1 Double side single through switch
S2 Push-to-on switch
S3 On/Off switch Pointed laser light
Chapter 7
Circuit Diagram
Figure 7- Circuit diagram of speed checker for highways
Chapter 8
Layout Design
Figure 8-Actual size,single side PCB layout.
Figure 9-Component layout for the PCB
Chapter 9
History of speed checker technology
In the past, the introduction of a new and innovative speed enforcement technology often
generated a negative reaction. The public's distrust of the use of high technology by
enforcement officials is often evidenced by claims that the technology is simply another
attempt by "Big Brother" to invade their lives. When radar was first introduced in the
1950's, Time Magazine ran an article headlined "Big Brother Is Driving," the text of
which characterized radar as being "as invisible as the Thought Police in Orwell's chiller
[1 9841. " 1 The use of radar was also challenged as being unconstitutional.2 The history
of speed enforcement is replete with examples of new enforcement techniques;
subsequentnegative public reaction and resistance; and finally, assumingsurvival through
legal challenges, ultimate acceptance.
Time-Distance Method
The use of the first known method of speed enforcement dates back to 1902 in
Westchester County, New York. This system wascomposed of three dummy tree trunks
set up on the roadside at 1-mile intervals. A police officer with a stopwatch and a
telephonewas concealed in each trunk. As a speeding vehicle passed the firsttrunk, the
hidden police officer telephoned the time to the secondpolice officer, who recorded the
time at which the vehicle passedhim and then computed its speed for the mile. If the
vehicle wasexceeding the speed limit, the officer telephoned the third policeofficer, who
proceeded to stop the vehicle by lowering a poleacross the road. The "tree trunk" method
was subject to hearsayobjections in court because officers had to testify regarding the
time statements of other officers since there was no way to observethe vehicle over the
entire distance.4
This is an early example of the time-distance method of speedenforcement. Time-
&stance measurements are computed by measuringthe time taken to traverse a distance of
known length.5 Severalmethods of speed enforcement employ the time-distance
principle.Pavement markings or mirror boxes that are observed by policeofficers with a
stopwatch have replaced dummy tree trunks, and two-way radios between patrol cars or
aircraft have replaced thetelephone system, but the technique remains much the same.6
The speedwatch, also referred to as the Prather speed device,was one of the first "electric
timers" to employ the time-&stancprinciples This device consisted of two rubber tubes
that werestretched across a street at a known distance apart. 'The tubeswere connected to
two switches, which were in turn connected to acontrol panel containing a stopwatch, a
switch, and a reset button.A police officer was positioned so as to observe both tubes, and
when a vehicle approached, he flipped the switch to activate thefirst tube. On contact
with the tires of the vehicle, the switch inthe first tube started the stopwatch, which was
stopped when thevehicle hit the second tube. The stopwatch was scaled to reflectthe
speed of the vehicle.8 The speedwatch is believed to have beenaccurate to within 2 mph,
and the officer's testimony as to hisobservation of the speeding vehicle and the accuracy
of the instru-ment was admissible in most courts.9
The most recent technique employing time-distance measurements
is the visual average speed computer and recorder (VASCAR). VASCAR is a
computerized system that mechanically computes the speed of acar by measuring the
distance between two fixed markers and the time traveled, thereby giving the observing
police officer a quick, easily readable speed determination. 10
In 1947, only 1 state used a time-distance device," but by 1970, 34 states were
employing at least one-the majority using VASCAR or aerial surveillance.12 Because
time-distance devices have been categorized as "speed traps," their use has been
prohibited in at least 2 states: California and Washington. 13
Pacing
Another widely used method of speed enforcement in the 1940's was "pacing."14
Police officers paced a speeding vehicle byfollowing it for a specified distance and
observing the speedometerof the police vehicle to calculate the average speed of the
pacedvehicle over the distance. In 1947, 20 percent of the states re-quired pacing before
apprehension of a speeding driver.15 A largepercentage of states used unmarked cars,
identifiable only bydecals, and/or motorcycles as pacing vehicles. 16 Because pacing
depends on the accuracy of the pacing vehicle's speedometer, manystates adopted the use
of calibrated speedometers and regulationsdefining the frequency at which speedometers
must be calibrated. 17
Tachograph
The tachograph, also referred to as a tactograph ortachometer, was a speed
enforcement method used by truckingcompanies to control the speed of truck drivers.
The tachographcontained a clock with a paper dial attached to the driveshaft or
transmission of the truck. The dial recorded the speed of the truck at any given time. 18
The chart produced by this device was used to corroborate the testimony of the arresting
officer;19 ironically,however, it was often admitted into evidence to prove the innocence
of the implicated driver.20
Radar
Police radar was introduced in the late 1940's and early 1950's. Although generally
referred to as "radar," police radar is not technically radar. True radar has the ability to
measure an object's distance, direction, and size as well as its speed, but police radar
measures only speed. Police radar operates according to the scientific principle known as
the Doppler effect: the frequency of sound waves (or microwaves) being emitted by or
reflected off of an object will vary in direct relation to the speed of the object itself. The
Doppler effect is noticeable in everyday life in the rising and falling of a car horn's pitch
as the car approaches and passes. Police radar transmits microwaves at a set frequency.
When the microwaves are reflected off of a vehicle, the frequency of the returning
microwaves shifts because the vehicle is in motion. This shift in the original frequency,
the Doppler shift, is measured by the radar device, which converts the
signal into a measurement of the vehicle's speed.
An early hurdle encountered by police radar (hereinafter called "radar") was evidentiary
in nature. Before judicial notice was taken of the underlying principle involved, courts
required that an expert witness testify as to radar's accuracy and re- liability.21 The
Virginia Supreme Court was among the first courts to take judicial notice of radar's
underlying principle, thereby eliminating the need for expert testimony.22 However,
testimony as to the accuracy of the particular machine used to detect the
violation is still required.
Constitutional questions have also arisen in radar cases, as they invariably do
whenever a new scientific technique becomes useful in enforcement.23 The Virginia
statute providing that radar evidence constitutes prima facie evidence of speeding was
found to be constitutional under the Fourteenth Amendment of the U.S. Constitution.24
The defendant in the case argued that the provision was tantamount to his being
presumed guilty25. However, the court held that the defendant was still presumed
innocent under such a standard.26 A Pennsylvania due process claim based on the alleged
instantaneousness of the machine's determination and the potential for error was likewise
denied.27 In denying the claim, the court noted the complete absence of cases holding the
use of radar for speed measurement to be unconstitutional.28 Cases raising the issue
of a citizen's constitutional right against self incrimination have likewise been
unsuccessful.29
Law enforcement's latest innovative technology for the enforcement of speed laws is
photo-radar. Photo-radar equipment combines a camera and radar with electronic controls
to detect and photograph a speeding vehicle. The unit can photograph the driver's face
and the front license plate if deployed to photograph oncoming traffic or the rear license
plate if deployed to photograph receding traffic. The license number of the speeding
vehicle is extracted from the picture, and a citation is sent to the registered owner of the
vehicle. The radar used in photo-radar equipment operates on the same Doppler principle
as the radar used by the police.
Although photo-radar is a relatively new technology in the United States, it is not the
first speed detection device to use a camera. In 1910, a device known as a photo speed
recorder was used in Massachusetts.30 The photo speed recorder consisted of a camera,
synchronized with a stopwatch, that took pictures of a speeding vehicle at measured time
intervals. The speed of the vehicle was determined by a mathematical calculation based
on the reduction in size of the vehicle in the photograph as it moved farther away from
the camera. This photographic evidence was held admissible by the Supreme Judicial
Court of Massachusetts, and the scientific approach was judged more reliable than,
eyewitness testimony because it did not rely on the "fluctuations of human agencies.
However, in 1955, the unattended use of the photo-traffic camera (FotoPatrol) was
prohibited in New York because of the difficulty in identifying the driver of the
vehicle.32 The Foto- Patrol device, a camera mounted on the side of the road
activated by an electronic impulse when passed by a vehicle traveling in excess of a
predetermined speed, took a picture of the rear license plate only, making it impossible to
identify the driver. The court was unwilling to adopt the presumption that the
driver was the registered owner of the vehicle, absent any corroborating evidence, and
prohibited the use of Foto-Patrol unless it was staffed by an attending officer available to
stop and identify the driver on the spot.33
The problem of driver identification was resolved by the Orbis In (Orbis) system
introduced in the late 1960's.34 Orbis operated much like an advanced Prather speed
device that employed a camera.35 The contacts the vehicle ran over were 72 inches apart
and connected to a computer that triggered the camera, which was set up to capture the
vehicle's front license plate and the driver's face if the vehicle's speed exceeded a preset
limit.36 When Orbis was introduced, it encountered a unique form of resistance. - 37 To
avoid being recognized, people would speed by the Orbis machine wearing a Halloween
mask. 38- Such a tactic would be illegal in Virginia, but not in Maryland, because of a
statute that prohibits those over 16 years of age from wearing a mask in public.39 Orbis
was abandoned for administrative reasons.40 Research did not identify any cases that
successfully challenged Orbis on legal grounds, and a study prepared for the U.S.
Department of Transportation indicated that the device was probably
constitutional.41
It is uncertain whether photo-radar will be accepted by the public. Previous speed
enforcement techniques usually gained acceptance if the technology proved accurate and
if they survived the initial constitutional and evidentiary challenges. However, even after
a technology gains acceptance, drivers have often undertaken efforts to thwart the
technology's effectiveness. One example of a popular form of resistance to speed
detection technology is the use of a radar detector. Radar detectors, which are illegal in
Virginia,42 sound a warning to the driver when they detect the microwave signal emitted
by the radar unit. Drivers have also tried using other methods to avoid being caught
speeding by radar.43 These methods included using transmitters designed to disrupt the
radar signal, putting nuts and bolts in the hubcaps, painting the fan blades with aluminum
paint, and attaching hanging chains to the undercarriage of the car.44 There is even a
160-page book entitled Beating the Radar Rap.45 Photo-radar will no doubt encounter
many, if not all, of these methods of resistance. However, if photo-radar is proven to be
accurate, and if it is able to withstand the initial legal challenges, then it should gain
acceptance as an effective tool in speed enforcement.
There is evidence that the public may support photo-radar use in residential settings.
In Pasadena, California, and Paradise Valley, Arizona, where photo-radar has been used
in residential settings on local, noninterstate roadways, a majority of respondents in
public opinion polls have been in favor of photo-\ radar use. However, one must interpret
these findings in light of the fact that more than 90 percent of those cited for speeding in
these two locations are nonresidents. This will not likely be the case in Virginia and
Maryland, especially if photo-radar is used on the Beltway.
Chapter 10
Purpose and Scope
The purpose of this study was to evaluate the feasibility of using photo-radar technology
on high-volume, high-speed expressways, such as the Beltway. A secondary objective
was to compare and contrast the performance of several brands of photo-radar devices to
determine whether they meet the minimum levels of accuracy, reliability, and efficiency
required for use on the Beltway in accordance with the U.S. legal system. In addition, the
impact of traffic characteristics on accuracy and reliability was examined. A final
objective was to make recommendations concerning the use of photo-radar on types of
highways other than urban expressways should photo-radar use on interstate highways
prove infeasible.
Information concerning the various brands of photo-radar equipment and their
capabilities was obtained from manufacturers' sales literature and was corroborated by
the results of several site visits. However, the most important information concerning the
performance of the various devices came from actual demonstrations on the Beltway and
other high-speed interstate highways in Virginia and Maryland. Thus, the feasibility of
using photo-radar was largely determined by the results of performance testing on site,
rather than by manufacturers' claims or nonempirical demonstrations in Europe and the
United States.
The scope of this project was rather limited. The researchers assessed the technical and
operational feasibility of the different types of equipment but did not evaluate the
effectiveness of the use of photo-radar in reducing travel speed or the number of speed-
related crashes since it was not possible to give citations during the demonstration period.
In order to avoid creating a hazardous environment for the manufacturers and the study
team, and to avoid disrupting the traffic flow at the study sites, no special signing
was used. In addition, media coverage was limited to a press conference on the second
Tuesday of each demonstration period. Thus, no fully coordinated media campaign was
employed. A further limitation on the scope of the study was that Multanova, one of the
major manufacturers, declined to participate in the demonstrations in Virginia and
Maryland. Therefore, there are insufficient data from which to draw conclusions
concerning the accuracy, reliability, and efficiency of Multanova's equipment.
BACKGROUND
Many people approach the use and evaluation of photo-radar as if it were a new and
uniquely invasive technology. In fact, photo- radar equipment is simply the combination
of several pieces of previously existing equipment-camera, radar, and electronic controls-
all of which have been used either together or separately in enforcement and the
prosecution of offenses for many years. The validity and reliability of these older forms
of speed enforcement technology had to be proved to both the police and the courts prior
to general acceptance. Thus, it is an important to consider the use of photo-radar in the
context of (1) the history of speed enforcement technology, and (2) the history of photo-
radar technology.
Chapter 11
Site Description
Site Demonstrations
During the summer of 1990, five manufacturers of photo-radar equipment
demonstrated their device on interstate highways in Virginia and Maryland for 2 weeks
each. A sixth, Multanova, was invited to participate in the demonstrations, but declined.
Many steps were taken to ensure a fair and equitable analysis of each company. During
each 2-week study period, the manufacturers were given the opportunity to take as many
pictures as they wished, using their choice of photographic equipment and
film.Manufacturers were also encouraged to take photographs using their equipment in as
many ways as possible so that each capability of the equipment could be evaluated.
Whenever possible, the film was developed by a local commercial laboratory. However,
when local processing was unavailable for unusual film types or unusual
canister sizes, other arrangements were made.
All demonstrations were conducted with the manufacturers or their agents operating
the equipment under the constant supervision of the research team, who collected the data
for all tests. Although the same tests were run for all pieces of equipment, there were
some differences in the manufacturers' experience in operating their device. For the most
part, these were based on the manufacturers' schedules, their familiarity with the
equipment, and whether all of the equipment's functions were working at the time
of the demonstrations.
There were, however, some conditions under which all of the manufacturers operated
that may have affected the performance of their device, such as the suitability of
permanent loop stations (and, thus, the study sites) for taking perfect photographs. In
these instances, since all manufacturers operated under the same conditions, no one
manufacturer had an advantage over the others.
The performance of each piece of equipment was evaluated after several tests were
conducted at the preselected sites. In order to prevent biasing of the desired information,
the same types of demonstrations were performed for each type of equipment at the
same sites, on the same workdays, and at approximately the same
time of day.
Site Selection
A major objective of this study was to determine how the prevailing traffic and geometric
conditions at a given site affect the accuracy of the speeds recorded and the clarity of the
resulting photographs. The ideal location for collecting the information to evaluate this
effectiveness would be where accurate volume and speed data could be collected and
where light conditions are nearly ideal for photography. The only sites at which speed
and volume data could be collected were at sites where loop sensors were permanently
installed. Unfortunately, these locations were not necessarily the best for photography.
Since the photographs could be taken at the loop sensor locations, and since it would be
virtually impossible to collect speeds and volumes accurately at high-volume locations
without loops, it was decided that the first criterion for selecting a site would be the
availability of loop sensors at the site. The next requirement was that the site provide
safe conditions for manufacturers, their agents, and those involved in collecting the data.
The final criterion was that the site be a two-, three-, or four-lane interstate highway with
suitable vertical and horizontal -alignments. Factors taken into consideration in
evaluating how safe a particular location was included the availability of adequate site
distance and adequate space away from the edge of the pavement for vehicles and
equipment.
In addition, the conditions at several of the sites necessitated that equipment be set up
in concentrations that may not have been ideal for photo-radar operation. In Northern
Virginia, for instance, each piece of equipment had to be set rather far back from the
roadway in order to ensure the safety of the public and the study team, due to the high
volumes and high speeds at these sites. This added an approximate width of one lane
to the distance between the equipment and the target vehicles. Also, at the I-495 site in
Virginia, there was a significant drop from the roadway to the shoulder that resulted in
vehicle-mounted equipment being tilted by up to 5 degrees. Thus, at this site, vehicle-
mounted units may in some cases have been projecting the radar beam over compact cars
and shooting photographs at an angle. These operational requirements, although not ideal
for the use of photo-radar, were equivalent for all manufacturers, thereby giving
none an advantage over the others.
The sites selected were therefore not necessarily the most ideal locations for photo-radar
equipment with respect to the quality of the photographs taken but were the most suitable
if all selection criteria were considered. Thus, it is quite likely that the photographs taken
did not represent the best quality that could be obtained by the equipment; however, they
served as a good means of comparing the photographic capability between brands of
equipment. Because of the safety criterion used for locating the study sites, it was not
necessary to use any special traffic control. The traffic pattern was therefore not affected
at any of the study sites.
Site Description
After considerable field evaluation of different sites with loop detectors, six sites were
selected based on the enumerated criteria. Table 2 shows the locations of the test sites and
the traffic and geometric characteristics at each site. Unfortunately, the ambient lighting
conditions were not perfect for photography throughout the day at each site. For example,
according to the field notes taken by the supervising technician, because of the angle of
the sun, Site 1 was not ideal for photography during the morning hours but seemed to be
much better in the afternoon, and the lighting conditions at Site 2 were not perfect for
photography in the afternoon. Similarly, the lighting conditions at Sites 4 and 6 seemed
better in the morning than in the afternoon, whereas conditions seemed better in the
afternoon at Sites 3 and 5. These were, however, subjective judgments made at study
sites, rather than empirically based findings.
Chapter 12
Utility
In order for a photo-radar program to run successfully, the equipment must be used in
such a manner as to produce clear pictures of speeding vehicles and, if necessary, their
driver. To determine which manufacturers produce the highest quality and most usable
photographs, an analysis of each photograph produced during the 2-week field
demonstration period was conducted. Due to the large number of photographs taken
during each test period (more than 7,600 total) and the careful scrutiny given each
photograph, the full evaluation of the photographs took about 5 weeks. Detailed
information concerning each photograph taken was entered into a computerized data set
as the photograph was being viewed. The specific variables used in the evaluation of each
photograph were:
1. manufacturer's name
2. roll identification number
3. date the film was exposed
4. time the film was exposed
5. location where the film was exposed
6. conditions under which the film was exposed (i.e., problems, problems with.
equipment itself, problems of equipment, problems with equipment itself and setup of
equipment, or problems with computer information strip picture)
7. direction of traffic photographed (oncoming vs. receding)
8. mode (stationary vs. mobile)
9. weather conditions when film was exposed (i.e., bright sun hazy sun, overcast,
nighttime, or raining)
10. whether prints or negatives were evaluated
11. number of vehicles in the frame
12. type of vehicle (i.e., passenger car, van/small truck, large
truck or bus)
13. lane in which the vehicle was traveling
14. location of the vehicle in the picture (i.e., no vehicle in frame, out of range left, in
left third of frame, in center o frame, in right third of frame, or out of range right)
15. whether the license plate could be read
16. reason the vehicle's license plate(s) could not be read (i.e. rain, glare, out of frame,
too far away, view obstructed, plate, reflectorization, or poor film exposure)
17. whether the driver was identifiable as compared to a standar photograph
18. reason the driver could not be identified (i.e., rain, glare out of frame, too far away,
view obstructed, receding traffic or poor film exposure)
19. whether it was possible to determine which vehicle w speeding (In cases where two
or more vehicles we photographed, a method was needed to determine which vehicle
had triggered the photo-radar photograph. If a method wa specified and it identified a
vehicle in the photograph, this variable was coded as a "yes.")
Information from each vehicle photographed was then analyze to determine what
percentage of a manufacturer's pictures could b in court, based on possible criteria for
photo-radar cases These criteria included (1) whether the license plate and the state
of issue were readable, (2) whether the driver could be identified (3) whether the vehicle's
speed was clearly stated, and (4) whether the speeding vehicle could be identified in
multi-vehicle photographs. In order to determine which vehicle in a multi-vehicle
photograph was speeding, several manufacturers provided a template. This clear plastic
overlay outlined where in the photograph the radar beam fell. The vehicle over which the
template's radar beam falls is the speeding vehicle. An additional manufacturer stated
that each template must be drawn based on the speed data for the particular site. Thus,
each site would have its own template. In cases where there were two or more vehicles in
the beam, some manufacturers claimed that their unit would not take a picture.
Other manufacturers stated that their unit would take a picture but that such a picture
would obviously not be used in a prosecution.
The effect of such factors as weather and distance from the camera on photographic
quality was also evaluated. In addition, at the start of the evaluation, photographic
standards for overall utility of the photographs were set, against which each
manufacturer's photographs were compared. These standard photographs appear in
Appendix A. Several of the photographs were enlarged to determine whether higher-
quality photographs could be produced for use in court. Two types of film were
evaluated: prints and negatives. The prints were viewed without any enhancements
except magnification. The negatives were evaluated by use of a viewer capable of
changing a negative to a positive image. The FOTOVEK U, a video-based viewing
system, allowed for the adjustment of contrast and focus and enabled the analyst to
magnify specific portions of the negative.
Accuracy of Recorded Speeds
The objectives of this test were to determine the relative accuracy of the speeds recorded
by each piece of equipment and determine whether the accuracy was significantly
affected by the prevailing traffic and geometric conditions. The tests were carried out at
Sites 1, 2, and 3. No attempt was made to conduct these tests on the Beltway because it
required isolation of the test vehicles from other vehicles, a practice that is difficult and
could be unsafe in high-volume, high-speed traffic.
Three test vehicles, a Chevrolet Cavalier, a Plymouth Minivan, and a larger Ford
Aerostar Van, were used in this test. The speedometer of each vehicle was calibrated
prior to testing. A driver was then selected for each vehicle and specifically trained
to drive that vehicle at the required constant speed as the vehicle traversed the loops at a
given site. The training required that numerous runs be made by each driver until he or
she could isolate the target vehicle from other traffic and could attain the required
velocity at a location about 150 feet from the loops, maintaining the constant speed as the
vehicle traversed the loops. Each driver comfortably demonstrated his or her ability to
meet the test requirements.
The next stage was to ascertain whether the speeds recorded by the loops were accurate.
This was achieved by having each test driver isolate his or her vehicle from other
vehicles on the highway and then drive the test vehicle at a given speed across the
loops while being monitored by standard police radar. This facilitated the clear-cut
identification of the speed of the vehicle as computed by a Streeter-Amet counter
connected to the loops and comparison with police radar. Prior to each test, at least five
runs were made on each lane by each vehicle for speeds of 40, 50, 55, and 65 mph. (It
was not feasible to perform this test at speeds higher than 65 mph because of the existing
maximum speed limit.) For each run, the speed of the test vehicle was recorded using
standard police radar and was compared to the speed computed by the Streeter-Amet
counter. The lane in which the test vehicle was driven was also recorded. In a few cases,
loop speeds for several of the 20 or more runs were off by more than 1 mph and were
recalibrated by VDOT personnel. Having ascertained that the vehicle's speed as measured
by police radar and that computed by a Streeter-Amet counter were within 1 mph of each
other, the test to determine the accuracy of the photo-radar equipment in recording
the speed of an individual vehicle was conducted.
The relative accuracy of the photo-radar equipment was determined by comparing loop
speeds to photo-radar speeds. The threshold speed of the photo-radar was set at 30 mph
so that the speed of each vehicle passing through its beam could be recorded and its
photograph taken. Each test vehicle was then driven at a constant speed through the test
site, isolating it from the other vehicles. The test was run for speeds of 40, 50, 55, and 65
mph for each lane and for each vehicle. For every run, the type of test vehicle, the
speed at which the test vehicle was driven, the speed recorded by the Streeter-Amet
counter, and the speed computed by the photo- radar equipment were recorded. The lane
in which the test vehicle was driven was also recorded. The speed recorded by each
piece of equipment was then compared with the actual vehicle speed as
obtained at the loops by the Streeter-Axnet counter. The accuracy of the photo-radar
equipment was determined from the variation between speed recordings produced by the
loops and those produced by the photo-radar equipment.
The testing was carried out under speed test conditions as specified in the federal
minimum performance specifications for testing equipment accuracy with respect to
temperature and supply voltage (NHTSA, Model Minimum Performance Specifications
for Police Traffic Radar Devices, Technical Report No. DOT HS 807-415, Washington,
D.C., May 1989). However, rather than the researcher using a stopwatch to determine
the average speed of the vehicle over a stipulated distance, a nearly instantaneous speed
reading was recorded by both the Streeter-Amet counter located at the loops and the
photo-radar equipment being evaluated. Thus, the speeds recorded by both the counter
and the photo-radar equipment were obtained at the same location and at the same time
and, thus, were instantaneous (or nearly instantaneous) measurements. This is a
much preferred and more accurate method than comparing the instantaneous speeds
measured by the photo-radar equipment with "average" speeds calculated by timing the
vehicles over the measured distance since the vehicle's speed would vary over the
distance preceding the photo-radar equipment.
Effect of Vehicle Clustering on Accuracy of Speed Measurements
The objective of this test was to determine the accuracy of the speed recorded by the
photo-radar equipment when vehicles were being driven in tandem across the loops. This
test was, therefore, a repeat of the speed accuracy test but with the test vehicles in a
paired configuration. This required careful driving on the part of the study team. In this
test, the test vehicles were driven in different lanes, with either the front of the vehicles
being on an approximately straight line when traversing the loops or with each
succeeding vehicle slightly offset behind the preceding vehicle. The speeds identified at
the loops and by the photo-radar equipment were then recorded and compared. The
results of this test indicate to what extent the arrival of two or more vehicles within the
radar beam of a piece of photo-radar equipment affects the accuracy of the speed
recorded.
Percentage of Usable Photographs of
Vehicles Exceeding Threshold Speed
This test was conducted at all sites when accuracy testing was not underway. At each
site, the photo-radar equipment being tested was properly positioned and set at a
threshold speed that ensured that all speeding vehicles traveling on the interstate were
counted. The thresholds were also set so that photographs of speeding vehicles could be
taken continuously for at least 3 minutes before the roll of film had to be changed. The
photo-radar operation was then initiated and allowed to continue for a given time period,
ranging from 3 to 15\ minutes, depending on the threshold speed, vehicle operating
speeds, traffic flow, and number of exposures available in the film canister. At sites with
a high volume and high operating speed (e.g., I-495), 5-minute intervals were generally
used since it took about 5 minutes to generate 36 photographs (standard film canister
size) without interruption. The test interval was increased to 10 or 15 minutes when a
larger number of exposures was available or when volume was low. This variation in the
test interval was necessary so that an adequate number of speed violators could be
photographed by the photo-radar equipment. Concurrent speed data were also collected
at the loops using the Streeter Amet counter, from which the number of vehicles
exceeding the speed limit for the same test period was determined. Two figures were
then computed:
(1) the number of photographs in which a vehicle's license plate number and recorded
speed could be clearly identified (as a percentage of the total number of vehicles
exceeding the threshold speed), and
(2) the number of photographs in which a vehicle's license plate number, the recorded
speed, and the driver's face could be clearly identified (as a percentage of the total
number o exceeding the threshold speed).
Misalignment Flexibility (Cosine Effect)
The objective of this test was to determine the extent to which misalignment of the
photo-radar equipment affected the speed recorded by the equipment. It was anticipated
that equipment might be unintentionally misaligned by untrained police officers. Each
piece of equipment was, therefore, set up in the operational mode but intentionally
misaligned from the manufacturer's recommendation by 2, 4, 6, and 8 degrees. The
speed accuracy test was then repeated. The speeds obtained at the loop sensors by the
Streeter- Amet counter were then compared with those recorded by the photo-
radar devices.
Ease of Detection by Radar Detectors
This test determined the maximum distance at which a commercially available radar
detector could detect the presence of the photo-radar equipment being tested. The radar
detector used was a Cobra Trapshooter, Model RD2100, manufactured by Dynascan
Corporation, Chicago, Illinois. After the equipment was installed at the test site, a test
vehicle with the radar detector installed was driven slowly toward the equipment until the
microwave radiation from the equipment being tested was detectable. The location was
marked, and the distance from the equipment was mea- sured. Each test run was repeated
at least five times, and the maximum detectable range for each manufacturer's photo-
radar recorded.
There are two possible effects a radar detector could have on the effectiveness of photo-
radar use. First, by knowing where photo-radar devices are located, drivers may avoid
citation by slowing down at the photo-radar site and then speeding up once they
have passed the site. Thus, radar detectors could reduce the effectiveness of photo-radar
in reducing speeds on other sections of the roadway. On the other hand, radar detection
of photo-radar equipment would, in itself, reduce speeds at the site, one of the
objectives of its use.
Effect of Photo-Radar on Speed Characteristics
Speed data were collected at each site at least 1 month before the field demonstration and
again during the demonstration. No citations or warnings were given during the test
period, but the minimal media attention given as a result of the Tuesday press
conferences may have alerted drivers to the presence of the equipment for testing. This
publicity took the form of newspaper articles and television and radio interviews in which
the principle of photo-radar was described and the reasons for conducting the
demonstration were explained. It was, however, made quite clear to the public that no
citations would be given based on speeds observed and recorded during the
demonstration. As an additional confounding factor, police consistently worked radar
during the demonstration at Site 6 in Maryland. Since this was their standard procedure, it
was decided that they should continue so the units could be evaluated under real-world
conditions. However, the use of standard radar during the testing may have affected the
speed characteristics at that site.
The researchers are of the opinion that the true impact of photo-radar on speed
characteristics could not be ascertained from these results. Then citations and warning
letters are given, it is likely that the impact of photo-radar on speed characteristics, such
as the mean and 85th percentile speeds, will be different from that reported in this study.
Chapter 13
View of Project
Figure 10-Glimpse of project
