This is simply a roadgeek glossary inspired by Ambrose Bierce's Devil's Dictionary (1911), with similar tone and world view. Definitions by Kurumi unless noted.

Updated Sept. 15, 2006. (new link to Missouri page)

AASHTO, n.
An agency charged with a biennial review of highway numbering, as well as miscellaneous lesser tasks.
Alternative, n.
One of several pretend activities the EPA might require a DOT to contemplate doing instead of its planned project, such as improving a different road or coercing higher bus ridership. However, the "No-Build" alternative is, in certain states, implemented quite often.
Arizona Highways, n.
A periodical now true to only half its title, but for history's sake still shelved alongside Public Roads at your university.
Auxiliary Lane, n.
An extra passing lane, created for space reasons to the right. Careless passers, however, may find themselves taking an unintended exit.
Bus, n.
A transit vehicle that, once a man's income exceeds a certain level, he can never be persuaded to ride.
Bypass, n.
A means of spurning yesterday's congestion in favor of today's.
Carpool, v.
To share a ride with someone who lives where you do, works where you do, and does not mind stopping by the bank, your child's soccer practice, the dry cleaners, and the gym.
Cloverleaf, n.
1930s An exciting innovation. 1990s An obsolete deathtrap.
Control City, n.
A warning; the dire fate awaiting the traveler who does not promptly exit this highway.
Diamond Interchange, n.
A low-cost, low-profile facility advocated by manufacturers of traffic signals.
Elevated Highway, n.
A facility to preserve right-of-way for a future depressed or tunneled highway.
EPA Region 1 - New England
The eye of a needle.
Expressway, n.
Eastern U.S. Freeway; Western U.S. Divided highway, access partially controlled
Freeway, n.
Western U.S. Divided highway, access fully controlled; Eastern U.S. What they call expressways on "CHiPS".
Frontage Roads, n.
A means of crossing Texas without ever getting on a freeway.
GIS, n.
The department responsible for releasing online maps in a format that invariably requires downloading a new 3MB plugin.
Gore, n.
A short-term parking area, marked with diagonal lines, where the decision of whether to exit the highway can be made at one's leisure.
HOV lane, n.
A special lane requiring each vehicle to have at least two riders. In some locations the minimum is three. After sunset the practical minimum is one.
Induced Demand, n.
The tragedy of a highway, once built, being used as intended.
M- route, n.
A state highway in Michigan. Should the Union in the future admit another state beginning with M, this convention would have to be changed.
Metering lights, n.
The discovery that one can get more drunk without vomiting by sipping one's beer.
Michigan left, n.
A maneuver in said state that begins with a 90-degree turn to the right.
New Jersey Turnpike, n.
An ingenious thoroughfare familiarizing the traveler with all aspects of the Garden State, so that sweeping generalizations may later be made therefrom.
No Thru Traffic
Indicates a convenient shortcut fronting one or more residential properties. Sadly, its destination is usually not documented, and must be discovered empirically.
Non-Chargeable Interstate Highway, n.
Part of a longitudinal study of Randian objectivism, namely, whether any city will be special at the time when all are.
Numbering Rules, Interstate, n.
A system for the sake of whose consistency the Ohio Turnpike is said to carry Interstates 80, 90, 76, 84, 86, and 88.
Pork, n.
A federally funded highway improvement located outside your congressional district.
Route 66, n.
America's most prestigious national highway, reaching only halfway across its breadth and missing by a thousand miles its most important city.
Rural Character, n.
A non-renewable quality which can be destroyed by adding lanes on a road, but is apparently immune to the retail zoning up and down its length.
"Slower Traffic Keep Right"
A saying of uncertain origin, possibly a phonetic translation from an extinct language. Generally acknowledged to have no semantic value.
SPUI
A type of diamond interchange named after a student at MIT.
Toll, n.
A fee charged for the privilege of using a highway or crossing. The money collected may fund: bond payoff; construction of another facility; continued operation of the toll authority; the transportation fund; the general fund; or the Mob. A tollgate also accrues goodwill over the years, which may be redeemed in the future by the authority deciding to dismantle it. A tollgate also subdivides the most ideologically pure of the privatization advocates, into those who claim the benefits of a government-subsidized facility free to the public, and those who do not.
Traffic Calming, n.
The idea that enraging the motorist will prod him to select a different route.
Urban Renewal, n.
The practice of clearing a slum by aiming a freeway at it.
Variable Message Sign, n.
A freeway sign with programmable display for the purpose of announcing sports championship results, missing children, and the benefits of buckling one's seatbelt.
Wetland, n.
Swamp.
In the mood for other Devil's Dictionaries? Try: