There are several ways to identify a point within the United States. The most accurate and least ambiguous way is that of global coordinates. These, of course, can be used to locate any place on the globe with two numbers: the latitude, which is a number between -90 and +90 and which indicates the location in a north/south direction, and the longitude, which runs from -180 to 180 and indicates position in the east/west direction; these units of these numbers are called degrees. The numbers can, of course be fractional; for example, the capital building of Wyoming in Cheyenne is at latitude 41.13553 and longitude -104.82134. Traditionally, degrees were divided into minutes and seconds, 60 minutes to the degree and 60 seconds to the minute, but that is less useful for computers, so we use the equivalent digital format. All the locations within continental US lie between 25 (south-most) and 49.3 latitude and -66.8 (east-most) and -124.8.
A degree of latitude extends approximately 71 miles from north to south; a degree of longitude would do likewise at the equator, but within the continental US is extends between 64 miles in the south to 46 miles in the north, in the east-west direction. Therefore when these coordinates are expressed to 5 decimal places (as Streets and Trips always does) a single digit difference in the last place (.00 001 degree) is, at most, about 45 inches. Placements are therefore usually expressed with much more precision than needed, and the real coordinates of an area the size of a truck stop can vary considerably and still be within the premises of the object. TruckTrek generally attempts to mark the location of a truck stop or other location so that the local roads are accurately indicated. In the case of truck stops, the coordinates are generally centered on the fueling bay.
The next location system generally used is the mailing or street address system. This system has a lot of problems from a computer user's point of view, and is not much used by TruckTrek. However, it will, of course, be important to a trucker when one is attempting to locate shippers or receivers, as their street address is the only information usually given. Streets and Trips does a good job of running down addresses and pinpointing their approximate locations, usually within a couple hundred feet.
Most roads in the US have names and numbers. The hierarchy of such roads, and their manner of notation in TruckTrek is:
Note that many state roads are being built today to near Interstate standards, but are simply never declared as Interstates for various political and financial reasons. California-99 is a case in point.
One new style of place locations has sprung up with the Interstate Highway system, and has subsequently spread to other highways as well, though not uniformly. This is the state/highway/mile marker system. All Interstate Highways are marked with small signs which indicate the distance in miles from the west terminus (for even numbered highways) or the south terminus (for odd numbered). Any location along such a highway can then be identified by the combination of state, highway number and mile marker. The state is usually known from context, so the notation "I-70 x59" indicates mile marker 59 along I-70, which should be 59 miles from the west edge of the state where I-70 entered or from where it originates. Mile marker locations are usually considered good if they are within a couple of miles of accurate; the states define a standard mile marker location for all interchanges, and they are usually identified by that mile marker.
That's the ideal; but there are exceptions to this simple system. One interstate in Arizona is marked in kilometers (kilometers are sometimes referred to as "klicks", and a kilometer is about 5/8ths of a mile). The kilometer markers have the abbreviation "km" on them.
Several states were slow to adopt the mile marker system; for example, California preferred a county based mile marker system rather than state based, and has been slow to adopt the standard used elsewhere. Utah has recently re-marked their north/south highways, causing confusion between old and new mile marker numbers; see the links below for others. Some states (New York, Delaware, Massachusetts, Connecticut, Rhode Island, Vermont, and New Hampshire, and New Jersey for the New Jersey Turnpike only) number their interchanges sequentially rather than by mile marker, and for these TruckTrek uses the notation "I-90 q4 x54" to indicate a spot on I-90, after interchange 4 but before 5, between mile marker 54 and 55. Some states, such as Illinois, don't number their interchanges for some of their highways at all. Then there are the state toll roads, which are not part of the Interstate System themselves, but may well incorporate parts of interstate highways in their turnpikes. Florida, Oklahoma, New York, Pennsylvania, Massachusetts, Illinois, Kansas and Texas are some of the states with toll roads, which have names rather than numbers.
In many places a pair of interstate highways will merge for a while. When this happens one of the numbering systems is used and the other suspended; if the highways unmerge further down the way, they both continue numbering as if they'd been numbered separately right through the merge. Thus the merged portion of I-64 and I-75 in Lexington, Kentucky is written as I-64/75, and the order indicates that I-64's marking is used in the merge. In Wisconsin there are three interstates occupying one strip of pavement (I-39/90/94). The first interstate named in a pair or trio of names is the one whose numbering is used along the common stretch. This is usually fairly straight-forward, but there are some merged roads where the natural numbering proceeds in opposite directions, such as I-81/77 in Virginia. That can be confusing, as the numbering on the non-dominant highway stops increasing, jumps to some other value, decreases, jumps again, and then continues upwards. In addition, as mentioned above, many state turnpikes occupy parts of Interstate Highway routes; where they do, the turnpike mile markers prevail, and they sometimes do not follow the eastward/northward rule (as with the New York Turnpike), and thus cause partial numbering along those routes in a reverse manner. Nothing is ever easy all the time!
Many states have extended their mile marker system to include other federal and state highways, and where known, values along these highways will be given. In general, though, the precision of locating a place on the interstate system is not available on US, state or local highways. In some cases the notation "highway & highway" is used to indicate the intersection or meeting place of these two highways. "highway @ highway" is similar, except that the location is on the first named highway near where the second intersects or meets the first.
Finally, locations can be identified by town and state. In practice, this uses the post office and state of the location's mailing address. Fortunately Streets and Trips readily provides this information. On the other hand, like addresses, these can change, as, for example, when a new post office is built. Almost all the resources identified in TruckTrek have a town and state assigned for easy informal, rough location.
Some web sites which detail the Interstate System:
TruckTrek and the contents of this help file are
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