This legend is divided into the following sections:
good source of basic terminology is the misc.transport.road FAQ.
I try hard not to use routing and alignment interchangeably, because they do not mean the same thing. However, the terms may blur for special administrative situations.
Business routes appear in Roadgap with the abbreviation BR, or occasionally BL if explicitly designated as a Business Loop.
At the present time, there are 80 designated High Priority Corridors created by these four component acts, shown here on this table hosted by Andy Field.
The pentagonal shape and approximate gold on blue/purple/indigo colour scheme is fairly uniform nationwide (and is in fact an MUTCD [q.v.] standard), though its exact design and layout may vary.
With the exception of California, Iowa and Wisconsin, county routes in the
United States use a county-assigned number. California and Iowa, however,
assign a county-dependent letter code and a number, and in
Wisconsin, typical county routes are eschewed in favour of lettered
historic county trunk highways (q.v.). Counties may also have secondary
county routes; typically, these are unmarked and the distinction is purely
a legislative one, but some counties mark them for historical reasons with
their own local markers (such as the Lassen
county secondary county route system in California).
Rarely, county routes will carry business route or loop (qq.v.)
alignments, such as portions of BR 395 in Ridgecrest,
Missouri has lettered highways too, but these are actually state routes, not county routes!
Compare with county route, which is their functional equivalent in other states.
Not all highways in a state may have exit numbers, even when true freeway-standard (q.v.) (example: Texas).
The last state holdout on exit numbers numbers was California, having obtained a waiver in 1971 due to the expense of converting signage, although they are now (as of this writing) being introduced and signed. This process, unfortunately, is being done in many cases by replacing signs entirely thus causing a great amount of sign history to be lost; some signs were up for decades before their destruction under this plan. California's original deadline to complete conversion was November 2008, but while exit numbers are officially on the books in many places, many of them are still not signed.
Although Forest highways are funded by the federal government and notionally run on federal land, states and local governments may handle their maintenance and thus routes that are existing US or state highways remain such (whereas within a National Park a US or state highway is not state highway, instead being maintained as a federal road; this is why US 20 is longer than US 6 but US 6 has more continuous miles, even though US 20 is connected through Yellowstone National Park -- the road which connects the two parts of US 20 is not, in fact, part of US 20).
Below the Forest highway level are various secondary routes. These rarely use the standard shield and may not be signed at all (when they are, they usually use four digits on a smaller rectangular shield). Although maintained to lower standards than primary Forest highways, they are still generally suitable for most low-clearance passenger traffic as long as care is taken. A tertiary set of routes are generally marked on maps only and in the field rarely, and are intended only for high-clearance vehicles and professional forest equipment. The specifics of these secondary and tertiary numbering systems may vary wildly from forest to forest.
Incidentally, Interstate highways (q.v.) are not considered Forest highways, even when they cross National Forests, because their controlled access (q.v.) restrictions effectively prohibit them from serving the purpose of a Forest highway (i.e., increased access to the forest). However, they may furnish access to non-controlled-access routings, and these might be.
Forest highways appear in Roadgap with the prefix FH.
Virtually all Interstate highways (q.v.) are freeways, except for rare specific exceptions.
A Super 2 is a special case of freeway where there is only a single lane each direction with no physical separation between the two (except for painted lines, of course, which don't count), but has all the other attributes of a freeway, including fully grade-separated interchanges. Analogously, there are also Super 4s.
Legislation introduced 20 September 1963 sought to remedy both issues before they snowballed, introducing four important dicta: 1) no more LRNs -- the legislative route number of a highway shall be the same as its signed number; 2) "one number equals one highway," i.e., do away with multiplexes wherever possible; 3) no duplicate numbers, e.g., no US highways or state highways having the same number as an Interstate; and 4) since LRNs were now gone, a new internal accounting method based on postmiles (q.v.) was to be established. This was combined with an AASHTO (q.v.) policy to prevent the proliferation of US highways -- routes under 300 miles entirely in one state are no longer to be US highways -- and the large amount of new Interstate with duplicate numbering being built to generate a huge cascade of numbering changes. These changes became effective on 1 July 1964, hence the official date of the Great Renumbering.
Here's an example that illustrates these principles at work, using US 60, US 70 and US 99; I've simplified this a little bit but the general idea is the same. These routes often ran multiplexed with each other historically (sometimes all three together simultaneously), and the area in which they ran was also to be the site of the future Interstate 10. As multiplexes were verboten, a single mother route was selected, in this case I-10 as it was to yield the most advantages for transportation. This decision had a cascade of consequences. First, because US 70 was never signed by itself in California, only ever with US 60, US 99 or both, it suddenly ceased to exist in the state (no multiplexes). Furthermore, as the only portion that remained solely US 60 had been now reduced to a short stub between Los Angeles and eastern Riverside county, it could no longer be US 60 (AASHTO policy on US highways), but as it was still state road, it became CA 60. Moreover, this left portions that were solely US 99 split up in pieces, none of them large enough and thus eligible to stay US highway either because of I-5 encroaching on US 99 as well. The biggest portion of US 99 became CA 99, but the other pieces were still state roads too, just without routings, so they were assigned to various different and sometimes totally new routes (including CA 86 and others) because numbers could not be duplicated.
Predictably, this had its biggest effect on US highways both because of the preference for Interstate highways where the two ran together or nearby, and because of the aforementioned AASHTO policy governing their routing standards. This caused US 6, US 50, and US 101 to be shortened, and US 40, US 60, US 66, US 70, US 80, US 91, US 99, US 101A (US 101 Alternate), US 299, US 399 and US 466 to be totally obliterated as US highways in California. Some of these routes eventually faded completely nationwide, such as US 66. (US 48 was long gone, earlier absorbed into US 50.) However, signage for these routes remained for some time as an aid to motorists even though the routes themselves were now defunct. I use the acronym "BTGR" (q.v.) to refer to a route number as it existed Before The Great Renumbering, and "ATGR" (q.v.) to refer to the route number (if any) a particular alignment of the old route carried After The Great Renumbering.
US 95, US 97, US 199 and US 395 survived this threshing virtually intact, although US 395 would be shortened for other reasons in 1969. Casey Cooper talks about the 1964 highway renumbering, as he refers to it, in great detail.
I give California's numbering shift special attention not only for it being
my home state, but also because it eliminated or significantly altered
years of highway history and many venerable national routes in one cascading
legislative spasm. In fact, I venture to say that no state renumbering shift
has had as large an effect on American national highways;
naturally, other states have had their own notable shifts
in numbering, but these changes have primarily been limited to state route
numbers instead and thus were more parochial in impact. As an example, in 1976
(and consummated by 1978),
Nevada changed almost every state route number into a three-tier grouped
system organized by county, all routes having three digits.
Only four exceptions (NV 28, 88,
140 and 266) maintained their numbers after the shift, as did dirt routes
NV 8A and NV 34. This process was complete by 1980; see Andy Field's table of
numbers. Note that this did not affect Interstates or US routes, nor did
Washington state's shift in 1964/1970 from purely numeric primary routes and
suffixed secondary routes to the present state highway numbering system
(that shift is documented
here), nor did the 1930's
With a very few notable exceptions, all routes signed as Interstate, even non-chargeable mileage, must meet certain requirements: complete control of access (see controlled access, essentially freeway [q.v.] grade), minimums for travel lane and shoulder size, and minimum design speeds. Under present federal law (specifically the Intermodal Surface Transportation Efficiency Act [ISTEA] of 1991, in 23 USC 103), funds are provided for construction, maintenance and (where it does not change capacity) reconstruction. This funding structure is quite different from the US highway system (q.v.), which has since been relegated to second-tier.
Interstates usually have two digit numbers; three digits indicates a
diversion from a mother route, either a loop bypass or beltway (qq.v.)
even) or a spur (q.v.) (first digit odd). Although even routes
run E-W and odd routes N-S, just like US highways, numbers increase
going northeast. Major N-S routes end in 5, not 1, and while numbers ending
in 0 are significant E-W routes, they are not necessarily transcontinental
like US routes are (or, depending on alignment changes, historically were).
Thus, I-95 runs border-to-border on the East coast while I-5 runs
border-to-border on the West, and I-10 runs cross
country south of I-80. These rules have remained consistent for a great
many Interstates, but there are a couple of oddballs;
probably the most egregious numbering
exception is the rancorous I-99, which was numbered
stone law without regard to existing convention by idiot Rep. Bud
Shuster (R-Pennsylvania) -- another reason why politicians suck.
Despite being isolated, Hawaii, Alaska and Puerto Rico have Interstates,
The Federal Highway Administration (q.v.) has administrative oversight
over Interstate highways, and has an excellent summary of
Interstate history, regulations and present routes. Interstate highways
are all part of, but not synonymous with, the National Highway System (q.v.),
and are not the same as the New
England Interstate highway system (q.v.).
The very observant will have noticed there is (intentionally) no Interstate 50, or for that matter, Interstate 60. Some thought about where these might run and what they would conflict with should reveal the reason. (Hint: what nationwide routes would be running in the same place due to their particular numbering system?)
Interstate highways appear in Roadgap with the prefix I-. Texas DOT
abbreviates them as IH.
Since LRNs are obsolete, I do not use them much except for historical reasons. When they do appear in Roadgap, I use the prefix LRN.
Most states use MUTCD mileposts on both Interstates and their regular state routes, and many municipalities will even use them on county roads. A significant number of states use MUTCD mileposts with "augmentation" such as printing the route number (Georgia [sometimes], New Mexico, Colorado [sometimes] ...), or may use non-standard mileposts that still act in the same function that a regular milepost would (New York's white Interstate tenth-mile markers, Pennsylvania's green tenth-mile markers, Indiana's blue mile markers, the common blue highway/direction/tenth-mile markers on Interstates in several states [Indiana, Ohio, ...], ...). These may deviate significantly from the MUTCD standard in appearance but because they still track total mileage within a state as mandated by the standard, I call them mileposts and not postmiles (q.v.).
Kilometre "mileposts" are in the field, by the way. One example is I-19 from Tucson, AZ to the Mexican border; even the exit numbering (q.v.) is in kilometres.
Mileposts in other countries are quite fascinating and sometimes ornate, depending on the age of the road. Some even act as primitive distance signage, indicating the next city or province and distance to it.
A specific milepost point is indicated in Roadgap with the notation
At its peak, the NEI highway system comprised 35 distinct routes, including suffixed alternate alignments, with its longest being NEI 1 stretching from New York City through Providence, RI, Boston, MA, and Bangor, ME to Calais, ME for a length of 617 miles. However, within just four years, the US highway system (q.v.) would be inaugurated and upon its legislative birth in 1926, the New England Interstate system was scrapped. Many of the NEI highway alignments were merged into the new US highway system, but had to be re-numbered as the numbering systems were not in general compatible; the only one that kept its designation was multi-state NEI 1, most of which became US 1 (and portions later US 1A). Of those that did not become US highway, many reverted to state highway instead and as such continue to carry their original numbers to this day.
New England Interstate routes appear in Roadgap with the prefix NEI.
For highways in Oregon, I try to report the OH number and/or name for the highway under study and, non-exhaustively, any other intersecting routes that are relevant to the discussion. When they do appear in Roadgap, as with convention on other Oregon roadgeek sites and the ODOT, I generally use the format OH #number and the route name in parentheses [example: OH #48 (John Day-Burns Hwy), which is part of US 395].
Please note that this is just my personal terminology; Caltrans is the only department that actually calls them postmiles officially.
The archetype postmile user is California, which just about exclusively uses postmiles on all highways, expressways and freeways. California postmiles track their enclosing county and reset their mile count at county borders (as opposed to MUTCD mileposts which do so at state boundaries), increase their count going north and east, and have tag letters indicating special circumstances that may affect the count (realignment, overlapping, etc.). Mileage counts may be fractional. These most often appear on black-on-white signs on the side of the road, but also appear on callboxes, lightposts and bridge signs. Daniel Faigin explains the postmile system in more detail. While California flirted with using MUTCD mileposts, their presence on California highways is considered a curiosity. The postmile system in California was established as part of the laws behind the Great Renumbering (q.v.), so they are not useful for tracing routes that were completely obliterated by that particular legislative action.
Nevada reformed their milemarkers to be much like California's during the 1970s, although unlike California, they do not use their postmiles exclusively. Besides the route number, Nevada postmiles carry a route designator (US or SR for Federal highway (q.v.) or state highway (q.v.) respectively), a county code, and generally an integer mileage count although fractional counts are also seen. Like California's, Nevada postmiles appear on small black-on-white roadside signs, and also increase their count going north and east. There is a class of Nevada postmiles for Interstate routes with the designator IR, but these are almost always accompanied by MUTCD mileposts and are not consistently seen on all Interstate alignments. There are also special classes for state roads that are not necessarily highways, such as FR for frontage roads, SP for state park roads, ER for escape ramps, AR for access roads and RP for 'roadside parking' such as lookouts and inspection stations.
New York uses a postmile-like marker affectionally referred to as a "Little Green Sign" but officially called reference markers by NYSDOT. RMs have a route number (with suffix if present), a region code, and a county count instead of county code referring to the number of times it crosses a county line; what makes RMs count as postmiles by my criteria is the fact that route distance resets at county lines and the markers also track city line crossings. These markers appear on all state routes, in addition to a white marker seen on Interstates that function like MUTCD mileposts but in tenths, and regular MUTCD mileposts. See this discussion on the NYS Reference Marker system.
A number of states don't have any kind of mileage posting on their non-Interstate highways (Maine, Virginia, Massachusetts, ...), which I suppose could be considered invisible postmiles of a sort ... ?
A specific postmile point is indicated in Roadgap with the prefix PM.
I try hard not to use routing and alignment interchangeably, because they do not mean the same thing. However, the terms may blur for special administrative situations.
American state routes appear in Roadgap with the postal abbreviation of
their state (e.g., Maine would be ME). For international state
highways, please refer to the blurb for that particular exhibit. For generic
state routes, I often use the abbreviation SR.
The distinctive white shield went through several revisions before the ones shown here. The top is the classic cutout shield in its modern incarnation, which remains in use in California (Virginia used similar cutouts until relatively lately, and they still survive in the field, but California is the only state to still specify cutouts in their state MUTCD [q.v.]). The bottom one is the MUTCD (q.v.) standard now used in most states, printed on a black square blank (the edges are exaggerated here) with a simpler shield design. Personally, I think the MUTCD US highway shields are quite dull and I think states should switch back to the fancier cutouts, as befits these venerable roads.
US highways are numbered on a grid system, odd being N-S and even being E-W, and the lowest numbers occuring in the northeast increasing to the southwest. Route numbers ending in 0 were designated as E-W transcontinental routes, and 1 as N-S "border to border" (thus US 1 on the East coast, and US 101 on the West, although this was more of a general principle [for example, old US 91 had no South border crossing, but did go to Los Angeles; similarly, US 101 never went to Canada, although it does terminate somewhere near it in Olympia, WA]). US 50, thus, is more or less in the middle. With the exception of US 101, three-digit US routes were numbered as spurs (q.v.) off a main two-digit route (e.g. US 202), although the even/odd rule regarding direction was not a requirement of these spurs, and sometimes there was only an indirect connection to the alleged mother route (for example, US 491 -- old US 666 -- never directly intersects US 91, its putative mother highway, but it does intersect US 191, which is a true spur). As US routes were winnowed after the rise of the Interstates, sometimes only the spurs remained (e.g., US 199). Certain classes of three-digit US highways ("3dus") do not have a putative parent, such as US 400, US 412 and US 425, and several highways were later renumbered in apparently abject disregard for the system (e.g., US 163).
Presently, AASHTO recommends that routes solely in one state under 300 miles be eliminated as US highways. Although a recommendation only, this stipulation was widely applied and would be a large contributor to the Great Renumbering (q.v.) in California.
Unlike Interstate highways, US highways are simply special cases of state highways (q.v.) with a different sign and a national grid number. This makes their designation as federal highways a bit of a misnomer; although they may have been constructed with some amount of federal aid, only a subset of US highways remain part of the nationally funded National Highway System (q.v.) and therefore in general their maintenance is paid for by the state they run within. US highways need not be freeways (also unlike Interstates), or even expressways.
US highways appear in Roadgap with the prefix US.
For still and archival photography, this means: 1) no use of photographs that are specifically not permitted for redistribution; 2) no alteration of content, other than cropping or labeling for clarity; and 3) clear designation of the actual copyright holder, where known, either in the accompanying text or labeled on the image itself.
For still video or movie frames, this means: 1) still frames only, without use of audio or animation; 2) no alteration of content, other than cropping or labeling for clarity; 3) clear designation of the movie or show from which it originates, either in the accompanying text or labeled on the image itself; and 4) clear designation of the actual copyright holder, where known, either in the accompanying text or labeled on the image itself.
Content layout guidelines
The introductory blurb discusses general background and history for the route or exhibit being presented. Supplemental material, including maps and photographs, may be used in the blurb. Many routes contain schematic routings I drew specifically for purposes of illustration, which may be slightly exaggerated or not to true scale for emphasis. The sources of the supplemental material(s), if any, are designated in accordance with the fair use guidelines I have established if they are not my own work.
In the two column section, all photographs appearing in the left column thumbnail list are entirely my own, and constitute the official portion of the photoessays.
In the two column section, the captions appearing to the right are entirely written and researched by me. Supplemental material, including maps and photographs, may appear to the extreme right within the caption boxes. In addition, photographs I have taken for purely supplemental purposes that for reasons of clarity, continuity or aesthetics were not included in the main photoessay, but may yield additional information on a particular picture, are also included. The sources of the supplemental material(s), if any, are designated in accordance with the fair use guidelines I have established if they are not my own work.