Floodgap Roadgap

Roadgap Conventions, Glossary and Guidelines

[Photograph: Future I-710 at Union St in Pasadena (photographed May 2005).]

What the heck ... ?

I'll admit it: I get a little jargon-crazy, and if you're not well-versed in some of the quirks of the American (and Californian) highway system, or roadgeeking in general, you might need this little document to set the stage.

This legend is divided into the following sections:

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Glossary (including terms and abbreviations I use)

Hopefully in alphabetical order. q.v. = quo vide (see also). Also, I use directional abbreviations frequently; NB = northbound, SB = southbound, and so on. Street and route abbreviations are more or less MUTCD (q.v.) standard: Fwy = freeway, Hwy = highway, Expwy = expressway, Ave = avenue, St = street, Rd = road, Cyn = canyon, Vly = valley.

Another good source of basic terminology is the misc.transport.road FAQ.

American Association of State Highway and Transportation Officials, responsible for national highway numbering, among other duties. Formerly AASHO.
The physical realization of a highway's routing (qq.v.), which is to say, the actual road itself. A routing may have multiple alignments if those earlier alignments have not been relinquished (q.v.).

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.

alternate route (ALT)
Alternative (often historical) alignment (q.v.) of a route to serve other areas, or to function as a bypass (q.v.) or safety valve during poor traffic conditions.
at-grade intersection
Intersection where there is no separation of traffic streams, i.e., no bridges or underpasses. At-grade intersections must be controlled with some sort of device, either stop signs or traffic lights. Compare with grade-separated interchanges. Strictly speaking, at-grade intersections shouldn't be called interchanges, but they often are (I make this mistake too).
After the Great Renumbering, a term I coined for route numbers established after the Great Renumbering (q.v.) in California. "ATGR" implies that the California route number or designation was different before the Great Renumbering for this alignment (q.v.). See also BTGR.
Circumferential route around a city. Probably the most famous is I-495 around Washington, DC (thus the expression inside the Beltway referring to federal government insiders). Compare with spur and bypass routes.
Before the Great Renumbering, a term I coined for route numbers established before the Great Renumbering (q.v.) in California. "BTGR" implies that the California route number or designation changed after the Great Renumbering for this alignment (q.v.).
business route, business loop (BR)
A route specifically designated for access to a city or town centre. Often business routes are former alignments (q.v.) of the mother route. In some cases, the business route may be an earlier highway replaced by a later one that now carries the business route (like old US 395 appearing as Business Route 15, with the new primary route being I-15).

Business routes appear in Roadgap with the abbreviation BR, or occasionally BL if explicitly designated as a Business Loop.

button copy
Today mostly associated with California, Connecticut and Arizona but actually used in a large number of states, button copy refers to special sign lettering with embedded reflective elements. Button copy was one method of complying with the MUTCD (q.v.) requirement for retroreflective sign lettering; older signs without these elements had them glued on, yielding an unsatisfactory result when grime would get spread over them by smog and rain. Nowadays, virtually every state is using reflective sign sheeting for new signage, including these three states, but there is still a lot of button copy out there on old or isolated roads.
bypass, bypass route (BYP)
A route branching off from a mother route to go around "pass by" a region, and rejoin it later. Bypass routes originating from Interstate highways (q.v.) are specially numbered with three-digit designations. Compare with loops, spurs and beltways.
Formally, the California Department of Transportation, but Caltrans is the official abbreviation (and typically used as a common reference). The term did not come into use until 1972, when Assembly Bill 69 consolidated the Department of Public Works and Aeronautics into the Department of Transportation (Caltrans) with six divisions (Transportation Planning, Highways, Mass Transportation, Aeronautics, Administrative Services, and Legal), replacing its former designation as the California Department of Public Works, Division of Highways.
California Highway Patrol.
Congressional High-Priority Corridor
In 1991, the US Congress passed the Intermodal Surface Transportation and Efficiency Act (ISTEA), designating 23 routes and corridors in the United States to be "high-priority" and potentially eligible for funds to facilitate the national highway infrastructure. This did not always mean Interstate highway (q.v.) construction, but did mean that special steps were to be taken to improve transport through the area as a national priority task, such as upgrading or widening of existing routes, in addition to formation or management of new Interstates and/or US and state highways (qq.v.). The ISTEA was followed by the National Highway System Designation Act (1995), the Transportation Equity Act for the 21st Century "TEA-21" (1998), and most recently, the Safe, Accountable, Flexible, Efficient Transportation Equity Act of 2005 - A Legacy for Users "SAFETEA-LU" (2005).

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.

control city
A likely destination of a particular route, signed on route signage to indicate direction by location (e.g., "SOUTH I-5 San Diego"). This yields concurrency and continuity in navigation. The MUTCD (q.v.) determines the list for national highways, although states may have their own internal lists for state routes.
controlled access
A road that does not have automatic right-of-way granted to owners of abutting properties. For example, you can't build a driveway directly onto such a road, although you could from a non-controlled road that this one intersects. Exactly what property owners can and can't do is, of course, codified by state law, but the Interstate (q.v.) highway system specifies its own requirements. Controlled access is inconvenient to property owners, but necessary to avoid accidents with traffic not moving at uniform speeds (such as traffic slowing down to turn into your driveway), and as such is part of the necessary definition of higher speed alignments (q.v.) such as expressways (q.v.) and freeways (q.v.). In many states, controlled access highways are marked with signs at the limit of the controlled access easement. These range from formal warnings to simply posts.
county highway, county route
[County route shield.] Minor local highway maintained by the county. Some may be former alignments (q.v.) of old routes since relinquished (q.v.). The quality of these roads and their suitability to through travel can sometimes vary widely from questionably improved dirt road to, in some extraordinary cases, full freeway (q.v.). Not all counties have county routes.

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, California.

county trunk highway
[Wisconsin county trunk highway.] Specific to Wisconsin; distinct from trunk roads and trunk highways (qq.v.). County trunk highways in Wisconsin were formally established in 1925, although many had been in development without official support as far back as 1918 as a result of 1907 legislation providing funding for county road improvement. They are most distinctive for their "numbering" system, which is actually done using letters, and may be up to three letters in length. County trunk highway designations are standardized across counties, and county trunk highway boards are responsible for maintaining their signed continuity. Here is an explanation of their history.

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.

divided highway
See dual-carriageway.
Term indicating that groups of lanes travelling in different directions are physically separated into two streams, not just with painted lines. Medians (q.v.) and Jersey curbs (q.v.) are some methods of separation.
exit numbers
Method of tagging exits with a unique numerical identifier as an aid to the motorist. Usually, this is the milepoint, with suffixes (A, B, C, ...) for multiple exits within the same mile. Some states use purely sequential numbering for exit numbers, but as the growing practise is to use distance this usage is disappearing and many states have converted their numbers. Yes, there are exit 0's in many states even though the MUTCD (q.v.) does not encourage this.

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.

A limited-access divided highway, which is to say, a road that does not have automatic right-of-way granted to owners of abutting properties (see controlled access) and has lanes travelling in different directions physically separated (see dual-carriageway). Intersections may or may not be grade-separated (q.v.). Compare with highway and freeway. All expressways are highways, but not vice versa. Similarly, the terms freeway and expressway are not synonymous.
Federal highway
[US highway shield.] See US highway.
Federal Highway Administration
USA federal agency responsible for oversight of the national highway infrastructure and determining standards and funding. The FHWA is a branch of the federal Department of Transportation.
See Federal Highway Administration. (The acronym is not FHA -- that's the Federal Housing Administration.)
Forest highway
[Forest highway shield.] A Forest highway, or National Forest route, refers to the highest level of road maintained in a US National Forest. Many times these are through roads, especially when they are routed over existing US highways or state highways (qq.v.), and often are paved. All such roads have a number, though this number is usually suppressed when co-routed with an existing highway; for routes not otherwise designated, the number is often (but not always) signed with the brown trapezoidal shield at left. All primary Forest highway numbers are two- or three-digit, and numbers are not unique nationally and may be repeated in separate forests. Their single purpose is to facilitate trunk-line access to the forest for recreational and commercial functions. For that reason, although many of them are through routes, many are not.

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.

A limited-access divided highway with grade-separated interchanges, which is to say, a road that does not have automatic right-of-way granted to owners of abutting properties (see controlled access), has lanes travelling in different directions physically separated (see dual-carriageway), and has interchanges with ramps or other devices to isolate traffic streams (i.e., no traffic signals or cross-traffic of any kind; see grade-separated interchanges). Compare with highway; all freeways are highways, but not vice versa. Also compare with expressway; all freeways are also expressways, but not vice versa. Finally, also compare with motorway.

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.

grade-separated interchange/intersection
Interchanges with ramps or connectors to isolate different traffic streams so that conflicts are minimized. With few notable exceptions, all US Interstate interchanges are grade-separated. Compare with at-grade intersections.
Great Renumbering, The
[US 101 Alternate is replaced by CA 1, as shown on the cover of California Highways and Public Works in 1964.] I use the term Great Renumbering to apply to any large-scale shift in a state numbering system, but the original "The Great Renumbering" is a term I coined for the events of 1 July 1964 on which a massive shift in numbering occurred in California. Prior to this, California had two separate numbering systems, the internal Legislative Route Number (q.v.) or LRN system, and the actual signed number. LRNs did not necessarily correlate with any one routing (q.v.), or even an alignment (q.v.) of a specific routing, and several routes could share an LRN; there were even many LRNs that never had highways routed on them. Furthermore, excessive amounts of route multiplexing (q.v.) as more and more route numbers were assigned -- particularly US, Interstate and even state highways (qq.v.) which might all share a single alignment -- yielded tremendous motorist confusion. At one time, for example, what is now signed I-215 through San Bernardino, CA was signed I-15, US 91, US 395 and CA 18 all at the same time!

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 Maine Great Renumbering.

In my usage, a designated conduit between points that has official recognition and/or funding for its maintenance, signage and existence. I use route and highway interchangeably for the purposes of this site, although shades of meaning may colour its use elsewhere. A highway need not be a freeway, or even an expressway (qq.v.), although both groups are necessarily highways.
High-Priority Corridor
See Congressional High-Priority Corridor.
High Occupancy Vehicle, pretty much meaning carpool. Usually referring to specific lanes designated for carpools only. In California, two people constitute a carpool except where otherwise indicated.
Interstate highways
[Interstate route shield.] The national Interstate system, or the Dwight D. Eisenhower National System of Interstate and Defense Highways, was enacted in 1956 and is now the top-tier United States national highway network. It was created for three distinct purposes: 1) to connect principal metropolitan areas in as direct as fashion as possible; 2) to serve the national defense; and 3) to connect to suitable border crossings where possible. Its combined component acts yield a mileage limit of 43,000 miles; routes that are part of the 43,000 miles and receive funding (under the Federal Aid Highway Act of 1944 and subsequent acts) are called "chargeable." There is also "non-chargeable" Interstate, which indicates additional routes (possibly built with some percentage of federal funding) built to Interstate standards and bearing an Interstate shield for logistic or continuity reasons, but not counting towards the 43,000 mile cap.

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.) (first digit 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 in 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, too. 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.

Jersey curb
Standard concrete divider with a thick tapered base and thinner top. This is in lots of states, not just New Jersey. This is one method of achieving a dual-carriageway (q.v.) configuration. Compare with median and K-rail.
Temporary movable tapered concrete barriers resembling Jersey curb (q.v.), but in fixed stock lengths and often chained or bolted together. Frequently painted white. This is a Caltrans technical article about K-rail use and convention in California. See Jersey curb.
Legislative Route Number (LRN)
Specific to California and indicates the old internal number for a particular portion of alignment, which did not in general correspond with the sign it carried (if it carried one at all). LRNs were used to denote the earliest system of state roads in California, but the initial signage of state routes in 1934 did not correspond to them and this set up a snowball of confusion over the next several decades. As a result, the old system of LRNs and stations was mercifully destroyed as part of the Great Renumbering and replaced by Caltrans' system of postmiles (q.v.). Compare with Oregon Highway numbers.

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.

limited access
See controlled access.
loop, loop route
Special case of a bypass (q.v.) where the route is specifically declared to branch out and then return. Sometimes used interchangeably for bypass.
Undeveloped strip, sometimes with landscaping or guard rails but often just plain dirt or raised concrete, physically separating groups of traffic lines in different directions. One method of achieving a dual-carriageway (q.v.) configuration. Compare with Jersey curb.
See mileposts.
[MUTCD standard milepost.] Officially reference location signs, USA mileposts utilize the MUTCD (q.v.) standard for marking distance along a signed route using white on green markers on the roadside, designed as part internal accounting and part motorist guidance. Although this post shows an integer mile count, fractional counts and even kilometre counts are permitted by the MUTCD milepost standard. Compare with postmiles.

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 Mile.

In the United States, this is a rarely-used term which is functionally synonymous with freeway (q.v.). In other countries, however, the term motorway either almost totally replaces the term freeway in parlance (example: New Zealand); or refers specifically to urban freeways; or (example: Australia) refers to urban freeways with a specific route number which are often toll roads (thus contrasted against freeways which are, obviously, free).
Manual of Uniform Traffic Control Devices, specifying how signage is to be designed and displayed. It is maintained by the Federal Highway Administration (q.v.). States may have their own such standards; some may deviate significantly from national practise (California being the most notorious).
Unofficial term referring to multiple routes being signed over the same alignment (q.v.).
National Forest highway
[Forest highway shield.] See Forest highway.
National Highway System
This is not synonymous with either the US highway (q.v.) system or the Interstate highway (q.v.) system, but specifically refers to all roads in the United States that receive special federal funding. All Interstate highways are necessarily part of the National Highway System because of their federal funding structure, but only a subset of US routes. Furthermore, the National Highway System also includes some state routes, and even some city-maintained roads. The Federal Highway Administration (q.v.) has a nice web page describing its scope.

New England Interstate highway system
[New England interstate shields.] Not to be confused with the modern-day Interstate highway system (q.v.), the New England Interstate Highway system emerged in 1922 after an agreement between Connecticut, Maine, Vermont, Rhode Island, Massachusetts and New Hampshire for a consistent numbering and marking system to replace the confusing local signage then in use. Under the new formalized numbering system, all routes were to be signed with a distinctive black and yellow sign (shown at left; the white border is only to demonstrate the edges) with numbering for interstate routes to be determined by consensus and less than 100, and routes purely within a single state to be determined locally (duplicates were permitted) with a route number above 100. Unlike US highways (q.v.) and the modern Interstate highway system, N-S routes were evenly numbered and E-W routes numbered odd, although this rule was only loosely followed. New York state also eventually joined the system for certain routes east of the Hudson River, although it did not follow the numbering system very religiously either.

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.

Oregon Highway System (Oregon Highway number, OH)
Specific to Oregon. Similar to the analogous system with California's Legislative Route Numbers (LRN, q.v.), Oregon initially determined a method of accounting for state highway mileage using highway numbers and names during the earliest allocation of state roads. When the Federal highway system (q.v.) emerged in 1926, the potential for numbering conflict was enough of a concern to create a parallel system of numbering, or the Oregon Route System. The Oregon Route number is what appears on signs and maps, while the original OH number and name is still used internally by Oregon DOT (ODOT) for accounting purposes. Unlike California's situation, the system in Oregon has never gotten congested or confusing enough to change it and thus it has persisted to the present day. Compare with Legislative Route Number.

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].

Oregon Route System
See Oregon Highway system.
postmiles (PM)
Postmiles, in my parlance, refers to any state-specific method of mileage accounting that differs from the MUTCD (q.v.) standard, as opposed to mileposts (q.v.). That is to say, a type of milemarker that does not track miles using the state line as an origin or terminus point, instead using some sort of intra-state boundary such as (typically) county, or (less commonly) city or township. Most postmiles minimally carry the route number and a mileage count; many carry the resident county or region, which may be encoded, and some carry a route designation as well. Unlike MUTCD mileposts, postmiles are usually not intended for motorist guidance.

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.

radial, radial route
A special case of a spur (q.v.) that radiates out from a central point, usually a city centre or downtown district.
reference location sign
See mileposts.
reference marker
See postmiles.
The process of returning an alignment (q.v.) back to the locality it runs through and decommissioning it as state or federal highway. This does not necessarily mean that the routing (q.v.) of that route is defunct, merely the particular alignment in question.
A person with brains who can read maps, and recognizes roads for the fountain of history they are. Male roadgeeks are amazingly studly, too. Just ask us.
See highway.
The idealized definition of a particular highway (q.v.), i.e., where law or regulation says the road is supposed to go. However, a routing may or may not have a corresponding alignment (q.v.) extant, especially if the road hasn't even been built yet, or may have multiple alignments where the older one has not yet been relinquished (q.v.). These situations notwithstanding, however, every highway must have a current routing to be considered a highway.


spur, spur route
A route branching off from a mother route that does not return to it. Spurs originating from US federal and Interstate highways (qq.v.) are specially numbered with three-digit designations. Compare with bypass and radial route.
state highway
[California state route shield.] A highway whose primary funding and maintenance are provided by the state. State route numbers are determined by the department of transportation in that state, as well as the shields they will use. In some countries (e.g., Australia prior to the new alphanumeric signage), the state highway shield is standardized between states. This shield type (a stylized miner's spade) is used in California.

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.

Super 2
See freeway.
trunk road, trunk highway
Not to be confused with county trunk highway (q.v.). A trunk road simply refers classically to any major thoroughfare, be it highway, expressway or freeway (qq.v.), and in some USA states was part of the original language establishing state highway systems. Nowadays in the United States this term is considered outmoded and rarely heard, but it is still used in Europe (particularly the United Kingdom).
United States Numbered Highway System
See US highway.
US highway
[US federal highway shield.] The United States Numbered Highway System, sometimes referred to as the Federal Highway System, was the first national road network as proposed in 1924 by AASHTO (q.v.), designed as navigation aids to motorists and to be no more than 3% of the total certified rural miles in a state. It was formally enacted in 1926, although not all states were signed at that time (for example, California did not have signed US highways until 1928), and not all routes were designated at that time either. The preeminence of the US highways was tarnished in these modern times by the Interstate system (q.v.), which took the US highways' place as the primary national road network, but many US routes remain important national arterials and co-exist or co-route with Interstate highways in many areas.

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.

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Content layout and fair use guidelines used

Fair use guidelines
Some copyrighted material appears on Roadgap that is not my own, particularly maps. In all cases, I have tried to reasonably balance fair use under international copyright law with the rights of the copyright holder.

For maps, this means: 1) no complete scans of any one entire map, nor the full release of portions that could be assembled to create any one entire map; 2) watermarking to prevent redistribution, while not obscuring relevant information; 3) no use of any maps presently in press, presently sold by the copyright holder, or less than five years old; and 4) clear designation of the actual copyright holder, where known, either in the accompanying text or labeled on the image itself.

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.

For copyright holders who notice their material used here, I hope this convinces you of my attempt to exercise fair use rights under copyright law to use it as educational aids for readers of this site, yet still respect your rights as the copyright holder. Nevertheless, if you have specific concerns over a use of your copyrighted material, please direct your questions to webmaster@floodgap.com. I reserve the right to request authenticated proof of copyright ownership.

Content layout guidelines

I have tried to use standard ways of handling my own content, and the content I have added to the site from other sources, particularly with respect to supplemental photographs.

In each exhibit is an introductory blurb, followed by two columns: a set of photograph thumbnails in the left column, with captions in grey boxes to the right.

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.

Please address suggestions or questions regarding this policy to webmaster@floodgap.com.
[Main page] All images, photographs and multimedia, unless otherwise stated, are copyright © 2004-2020 Cameron Kaiser. All rights reserved. All writeups are copyright © 2004-2020 Cameron Kaiser. All rights reserved. Unauthorized copying or duplication without express consent of the copyright holder is strictly prohibited. Please contact the sitemaster to request permission if you wish to use items from this page.

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