The E-ZPass System 
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(Autumn, 1997) 
By Big Brother

I am responding to the comments in the summer 1997 issue about the New York
State Thruway s E-ZPass system and its ability to identify a particular vehicle
for violation enforcement by using "secret detectors."

These "secret detectors" are probably nothing more than conventional radar
units, wired to a central location for recording data. If the "secret detector
units" are state of the art, they are video cameras feeding a video unit with
software that allows individual vehicle speed determination and recording. The
use of E-ZPass to cite speed violators is cumbersome and can only "average" the
vehicle's speed over a known distance, as I will explain below. Radar units, RF
or laser, or video systems are much easier to use for the actual speed
determination.

What is a "toll pass?" There are many types of toll passes in use. E-ZPass is
only one. To alleviate the paranoia concerning toll passes, let's understand
how the system works and with this understanding come the realization and,
perhaps, relief that the "authorities" sometimes really do try and make things
easier for the motoring public without always hiding some Big Brother device
among the goodies.

Transponders (a.k.a. "toll passes," or "tags") are used to identify the
location of a particular vehicle. When passing a particular location, a
motorist's location, time, and date will be recorded. Not the speed. It takes
two stationary installations to determine a vehicle's speed. The vehicle's
average speed is then calculated between these two known locations. There are
many ways to easily determine a vehicle's speed without trying to adopt the
E-ZPass type system to this use but, if they have enough stationary locations,
it can certainly be done. This is not rocket science. Let me explain (without,
hopefully, writing a booklet). The technical types might find this interesting.

Toll pass systems use microwave frequencies, usually in the 900 928 MHz, or 2.8
GHz, or (soon) 5.8 GHz bands to communicate between the stationary
transmitter/receiver and the vehicle transponder. Can you jam these
frequencies? Sure. If you do, and the system uses gated access, you will not be
granted access. So what good have you done?

Could you cause a signal that would indicate a lower charge than you should be
paying to be transponded? Some systems only query the transponder for its
unique identifier number. The central computer keeps the rest of the data for
the billing occurrence. This would seem to me to be impossible to "hack" at the
transponder end. Other systems record the entry time, location, etc. into the
transponder. Then, when the transponder is queried upon exiting, both the entry
and exit data are sent to the stationary receiver. There is potential here for
hacking. It is also federally illegal (two years and $10,000 per occurrence)
and not recommended. (Hey guys, there ain't no free ride. Somebody has to pay
for the road. Let the users pay or all of you nonusers will wind up paying for
the roadway via higher income taxes, fuel taxes, and so forth.)

900-928 MHz is the most common frequency spectrum presently in use. Want to
hear what the transmissions from the vehicle transponder sound like for a 900
MHz system? Place a cellular telephone near the transponder and depress the SND
key. The transponder will usually react to the nearby cellular frequency and
think it is being queried, hence causing a transpond. You will hear the
transpond as a burst of data in your cellular telephone's handset earpiece.
Record this for analysis. It is not encrypted and usually consists of a simple
multiple digit code. Depending upon the system being used, this transpond will
always contain the transponder's unique identifier code, and it may also
include the date, time, location of last time it was queried, and other
administrative information.

One commonly used toll pass system uses backscatter modulation to activate
vehicle transponders. From a stationary transmitter with the antenna mounted
over the roadway, microwaves are caused to impinge upon the vehicle-mounted
transponder, causing the transponder to power up, use some of the absorbed
microwave energy, and reflect ("backscatter transpond") back to a nearby
stationary receiving antenna, on another nearby frequency, with the transponder
s identifying code number (usually about eight digits). A central computer
records the identification number, location, time and date, and performs the
desired action. This is all that is required for entry verification to a
parking lot, etc. More normally, this initial information will be the entry
point to a controlled access tollway.

Intelligent Vehicle Highway Systems (IVHS) use a second occurrence of the
proceeding action, occurring at a second location, usually where the vehicle
exits the tollway. The central computer will then access the billed to account
and record this data for end-of-month processing into an invoice.

As you may have deduced, backscatter modulation is imperfect as a speed
determining medium. Within a distance of many meters there is no relatively
accurate method to determine just when the transponding action will occur. As
an aside, if the vehicle has one of the metallic impregnated windshields used
to reduce ultraviolet ray transmission into the vehicle, the transponder
(normally mounted inside the windshield) will have to be mounted on the outside
- usually in the area of the front bumper - so it is unshielded. But I digress.
Different stationary microwave transmitter/receiver combinations can cause the
distance-to-vehicle measurement to vary. Multiple vehicles being almost
simultaneously measured are another cause for error. At highway speeds the
inaccuracy of the distance determination is enough to potentially flaw any
attempt at speed measurement at a given location.

This same argument applies for battery-operated vehicle transponders. However I
do believe they would be inherently more accurate than backscatter types, even
though I do not believe their accuracy would be sufficient for speed
measurements over short distances. A counterpoint can be made that, if the
distances between the two stationary transmitter/receivers is great enough - and
I am not going to bother with the calculations but a quarter mile or so would
certainly do it - the distance inaccuracy in reading the transponder would be
rendered inconsequential and speed could be determined with sufficient legal
accuracy.

So why not measure speed this way? Each stationary installation will cost many
thousands of dollars. ($30,000 each is a good estimate.) And it takes two such
installations. Why complicate life when it is unnecessary? It is much easier
and vastly less expensive to perform the speed determination with radar and a
camera, or with a video system. Especially with a video system. Betcha this is
what the New York State Thruway is using!

If you want to join the modern age in speed enforcement you would use a pure
video system. Forget the radar; this system is undetectable. There are no
emissions and, consequently, nothing to detect.

Fully automatic video enforcement is not yet legal in all states. (Aren't you
lucky?!) However, the laws of some states do allow ticketing speed violators
via this method. Imagine a scene being photographed with the frame rate of the
camera being known. Therefore a vehicle moving between two known points on the
video picture can have its speed easily calculated. There are several systems
that can do this. You do not even need an actual known point of reference.

Some systems allow you to "draw" two lines on the screen of your video monitor
like the sportscasters do during a football game. When the vehicle crosses the
first line a clock timer begins. Crossing the second line stops the counter
and, bingo, the vehicle's speed can be calculated very accurately. When the
calculated speed is above an arbitrarily set threshold a freeze frame will be
captured and held. And, just to terrify you more, up to 26 lines can be drawn
on one video screen, meaning that up to 13 vehicles can be simultaneously
tracked. (You have to have one entry line and one exit line for each "detection
block.")

Lines can define detection blocks for each lane located adjacent to each other,
or they can be located in the same lane, perhaps a quarter mile apart, subject
to the video resolution possible. Different timing thresholds can be set for
each detection block. And the camera does not need to be near the site in
question, just have a clear field of view. However, since bad weather would
limit the system's ability to "see" vehicles, the camera(s) will usually be
mounted near the site in question.

infrared illuminators, which are really just floodlights operating in the near
infrared spectrum, the entire site can be flooded with light for the camera to
use, light that your eyes cannot detect; it will look dark to you and they can
still see you!

With a line drawn for height detection and a side-mounted camera, over-height
vehicles, usually trucks, can be detected and someone alerted to stop them. If
there are different speed limits for trucks and cars, this is how they can be
differentiated.

The resultant freeze frame will be automatically processed to produce a printed
picture of your vehicle from the rear, showing your license plate, and then
imprint the image with your vehicle's speed, the date, and time. AT&T is above
95 percent accuracy in doing optical character recognition on your license
plate and automatically entering the plate number into the computer system.
Imagine how easy those European license plates must be for OCR. Now if we could
just standardize the print and colors used on U.S. plates...

Not uncommonly, a second camera will simultaneously take a photo of the driver.
Look around when you see one camera and see if you can find the second one. It
can be mounted more than a block away from the site in question. Again,
location is determined by the ability of the camera to take a good picture in
adverse weather conditions. All of this results in a citation, including copies
of any photographs taken, being mailed to the address shown on the vehicle's
registration. Pay up or see you in court.

As another aside, in some states the use of the second camera to photograph the
driver has been considered an invasion of privacy and may not be allowed by
that particular state, hence they do not know who is driving the vehicle. It is
possible that the vehicle's owner may be held liable for the operation of the
vehicle. One case comes to mind where the citation, including the driver's
photograph and that of the incident passenger next to him, arrived at his house
and was opened by the driver's wife. Needless to say, as revealed in the
ensuing divorce proceedings, the driver had been thought by his wife to be
elsewhere and not in the company of the lady next to him! I believe this case
was sufficient to obtain the elimination of the driver's camera in that state
and hence prevent future incidents such as this from occurring.

I am somewhat sure, but not absolutely positive, that the New York State
Thruway is not issuing speeding citations solely via the use of the E-ZPass
system. Perhaps a reader is with that fine agency?

In closing, do not lose the convenience of the E-ZPass system because of
paranoia about speeding violation enforcement. If they want you they will get
you with much easier and more efficient incontestable methods!

And, no, I do not work for the New York State Thruway. But I would use their
EZPass system if I lived there.