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Hacking the Highway

[Editor's Note: The following was originally published in 2600 Magazine and later spotted on the Internet. For entertainment and educational purposes only.]

Hacking the highway
By: Mennonite
As published in the winter 2001-2002 2600 Magazine, Pages 40-41

I decided to write this because many people have often wondered if this sort of thing was possible, and have experienced disbelief upon viewing pictures of modified highway signs reading things like "Free Kevin," writing it off as the work of Photoshop or the GIMP in the hands of someone with too much free time. Hopefully this article will give you insight as to the way simple systems operate and encourage you to go out and explore similar systems such as electronic billboards.


The unit this article was written about is a fairly commonplace highway hazard information sign constructed by ADDCO and purchased by pretty much every state and county highway commission in the US. They are trailer mounted and can be powered by either portable diesel generators or solar panels mounted on top of the display screen with batteries for nighttime usage. The display screen is a three line by eight character display changed by flipping cards ( pixels ) that are yellow/reflective for on or black for off. At night a pseudo-backlight system can be turned on by switch or by photocell resistor. It is in fact not a backlight, but two orange bulbs at the bottom and top of the sign that illuminate the reflective cards causing them to glow. As far as access panels go, there are three. Two are at the front of the unit ( side facing traffic ) or along the sides. These house batteries and are usually locked to prevent people from stealing the batteries. The other access panel is at the back of the unit in the center and is seldom locked. This panel houses the control panel, various switches and other innards.


Open the rear access panel and look inside. You will most likely see a black panel with an old school IBM AT style keyboard velcroed to it. On the right of the panel will be a silver battery disconnect switch for changing the battery. Below the panel will be a battery status gauge measured in amperes. On top of the panel will be a controller on/off toggle switch. To the left, two three position toggles: a mast lower/off/raise switch and a backlight on/off/auto switch. The panel itself consists of a non-backlit LCD screen that displays eight lines by 48 characters. They keyboard itself appears to be standard with the exception that instead of an AT plug, it plugs into the panel via RJ11 jack in the style of the older WYSE dumb terminals. Due to the lack of insulation for about one inch before the rj11 plug, I am tempted to believe the keyboard was at one time a standard keyboard, but the AT plug was chopped off and an RJ11 plug was crimped on in place.


The display shows a preview of the six frames in rotation and invites you to press m for the main menu. After reaching the main menu you will have four paths:

  1. Turn off display
  2. Speed up rotation
  3. Slow down rotation
  4. More options ( password required )

The password in my case was DOT1. It was found after attempting to guess for about ten minutes, then glancing at the inside of the door where Password: DOT1 was scrawled in black sharpie marker. We tried this password on four other units where no password was written on the door and it worked on all occasions. Our Guess? DOT1 stands for Department of Transportation 1. After reaching the more options menu, you have six choices:

  1. Change current rotation
  2. Change/modify rotations
  3. Change/modify frames
  4. Change time
  5. Change time rotations
  6. Other options

The only options you'll wish to play with ( yes, it will allow you to change the system password, but please do not do this, it's not very nice ) are the change/modify rotations and change/modify frames. Say you wish to replace the current message with one of your choosing. You would do the following:

First select change/modify frames. It will give you a blank 8x3 matrix:

[        ]
[        ]
[        ]

Use your arrow keys to move about. To delete a character, use space on it to white space it out. Press enter when you have finished.

After you press enter, it will ask you if you wish to save your frame. Press enter to save it. It will then prompt you for the slot you wish to save it in. Slots 1-185 are preprogrammed with different useful things like road closed and detour. You can overwrite 1-185, but it will undoubtedly inconvenience someone at a later date so please don't do it. I usually start at 240 and go up from there because in most cases transit people tend to start at 200 with their own messages (region specific things like at blah road and blah) and go up. Forty frames is plenty of space for them. After you have created and saved all the frames you'll need (keep in mind you can only use six frames per rotation ), drop down one menu level by pressing enter, and then select create/modify rotation. At this menu, you will be presented with this:

[ ] [ ] [ ]
[ ] [ ] [ ]
[ ] [ ] [ ]

[ ] [ ] [ ]
[ ] [ ] [ ]
[ ] [ ] [ ]

It will start by asking you which frame you wish to modify. Press 1 followed by enter. It will then prompt you for the frame number you wish to insert. Type in your frame number (240) and press enter. The first cell will then be filled by the contents of the frame number you gave it. It will then again ask you which frame you with to modify. Press 2, then enter, and so on and so on. When you are done and it asks you what frame you wish to modify, press enter. The system will then ask you if youd like to save your rotation. There are 25 possible slots you can fill. Please use slot 25, as other slots may be filled with legitimate entries. After this is completed, drop down to the main menu and choose select rotation. It will then ask you which rotation you'd like to use. Tell it 25 and press enter. It will then say: Press Y to start. After you press Y your message will begin to flash across the front of the big sign and it will say press M for menu, and display the frames in rotation youre currently using.


The system default password, in my case DOT1, was housed in a ROM chip inside the unit. After successfully changing the system password, we attempted to restore the unit to its default password by turning off the unit and disconnecting the battery terminals via switch. This attempt succeeded. If the system default password is in fact not DOT1, then I wish you good luck.

Cover your ass, please. Do not modify screens that display information important to public safety, and by all means do not modify the contents of a sign if the sign's contents are necessary to prevent accidents or unfavorable conditions. Also: please do not modify the contents of a sign to read something that may possibly cause accidents or unfavorable conditions. If you do this, you are recklessly putting other people in danger and they may be injured or killed. With this in mind, I hope you have a good time replacing a signs content to display messages like: Free Dmitry, For a Good Time Call 1-800 your-mom. Thank you, and best of luck.


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