Site Navigation
Delaware Highways
Interstate-Guide
LoneStarRoads
Mid-Atlantic @ AARoads
NorthEast Roads @ AARoads
SouthEastRoads
Western Roads @ AARoads
 
 

AARoads Glossary

This page is provides some definitions of commonly used words and phrases on AARoads. We have tried to be consistent in our usage of each term on all AARoads pages. If you have any questions, please contact us.

  • AASHTO - the American Association of State highway and Transportation Officials is known as AASHTO. This organization consists of professionals from each of the states' highway and transportation departments. AASHTO is responsible for assigning route numbers for the U.S. route system.

  • Adopt-A-Highway Program - sometimes segments of highway might be "adopted" by a local organization as a community service. The organization members pick up trash and clean up the rights of way of the highway.

  • Agricultural Inspection Stations - in California, agricultural inspection stations guard all major points of entry. These stations are placed to help protect California's agricultural economy by preventing the accidental importation of infested fruits and vegetables from other states, including the Mexican fruit fly and other pests.

  • Alternate Route - sometimes a highway may have one or more alternative alignments through a certain area. Sometimes these alternate routes serve other towns and cities, while others provide a different method of passing through a city. Many U.S. and state routes utilize alternate routes to provide options. On occasion, the alternate route might be faster or shorter than the original route. Signage for alternate routes may have a banner above the sign that says "ALTERNATE" or "ALT." Other alternate routes may have the letter "A" suffixed onto the route number.

  • Appalachian Regional Corridors (ARC) - established by the Appalachian regional Commission, the regional development corridors are roadways in Appalachia that are slated to be improved to a minimum of four-lane highway standards. In some cases, the corridors are to become freeways. Some of this upgrading process is complete (such as Interstate 68), but several significant improvements remain to be completed (such as Corridor H/U.S. 48).

  • Arch Bridge - an arch bridge is a bridge supported by a concrete or steel arch underneath the bridge that directs pressure and weight of the bridge outward to the supports along the arch.
  • Arterial - an arterial is a major roadway in a city or urban area that collects traffic and feeds it to the freeway system. Arterials are usually the roadways first plowed after a snowstorm to ensure adequate traffic flow.

  • Auxiliary Routes - auxiliary routes include alternate, business, and bypass routes from a highway.

  • Auxiliary Signage - guide signs posted for an interchange or intersection displaying secondary points of interest or towns/cities that are beyond the main control point of the particular highway junction.

  • Average Daily Traffic (ADT) - the average daily traffic count is used as a method to determine how many vehicles travel on a road on a given day. This enables traffic planners to prioritize projects by comparing traffic counts to determine relative need. See also "level of service."

  • Banner - a banner is a rectangular sign above a route shield that varies in appearance depending on use. On reassurance markers, the banner indicates the direction of the route (north, south, east, or west). On trailblazer markers, the banner indicates the word "TO." On auxiliary routes, the banner would indicate if the route is an alternate, business, or bypass route.

  • Beltway - a beltway is a freeway that completely encircles a metropolitan area. Examples include Interstate 495 around Washington, D.C., and Interstate 465 around Indianapolis, Indiana. There are not as many full beltways west of the Mississippi River.

  • Botts Dots - commonly used as lane markings in areas where snowplows won't rip them off the pavement, botts dots are raised, polished concrete markers with rounded edges that are used to provide lane markings on freeways and surface streets. One benefit of these markers is that they make noise whenever a car crosses into another lane, which allows motorists to hear when they are making a lane change. See Caltrans' Botts Dots for more.

  • Bubble Back Traffic Light - traffic lights differ from each other based upon the manufacturer. One can identify some of the traffic light manufacturers by simply taking note of the back of the traffic light fixture. Bubble backs are traffic lights where each lens is backed by a bubble like molding. The brand name for these signals is McCain. McCain signals are installed more prevalently than Eagle, 3M, and other brand name signals because of their relatively low cost.

  • Bubble Shield - a bubble shield is a shield that is characterized by wide, curved lines to make a shield appear almost cartoonish. Interstate and U.S. Highway shields of this nature began appearing in the late 1990s.

  • Business Loop - a business loop is a surface street route that leads into a downtown business district and returns to the freeway at the other end. Frequently, the business loop is the alignment of the original highway before that highway was bypassed. An example is Business Loop I-83, which follows old U.S. 111 through York, Pennsylvania.

  • Business Loop Freeway - a business loop freeway (or freeway loop) is a freeway that is designated as a business route (green shield) of an Interstate highway. Business Loop Freeways are created as a result of a newer freeway route being constructed parallel to the original Interstate, and the Interstate designation is transferred to the new alignment. Normally, the older route is not up to Interstate standards, so it is not considered for a three-digit interstate designation. Examples include Business Loop I-80 in Sacramento, California; Business Loop I-40 in Winston-Salem, North Carolina; and Business Loop I-85 in Spartanburg, South Carolina. Business Loop Freeway status is being considered for sections of Interstate 40/85 in Greensboro, North Carolina, and Interstate 95 in Wilmington, Delaware. Yes, we count business loop freeways on our clinched Interstates list, even though they are not technically Interstate highways.

  • Business Route - a route that connects the freeway or through highway with the downtown and commercial areas of a city or town are found along business routes. The business route is typically the original alignment of the highway before a freeway or bypass route was constructed. Interstate business routes are identified by green business loop or business spur shields. A business loop implies that the business route will return to the parent route, while a business spur implies that the business route will only spur into the commercial area and not return to the parent route. U.S. and state routes frequently identify their business routes with a "BUSINESS," "BUS," or "BUSN" banner above the shield. Almost every state in the United States uses business routes for its Interstate, U.S., and/or state routes.

  • Business Spur - a business spur is a surface street route leading from the Interstate highway into the central commercial district. The spur route ends upon reaching a specified point within that urban area. An example is Business Spur I-44 into Fort Leonard Wood in Missouri.

  • Button Copy Signage - button copy signs are guide signs that have reflective buttons within each letter on the sign. Before 3M and other sign companies patented the current sign sheathing in use, button copy was generally the preferred medium for all guide signage. Ohio and Arizona were the last two states to install button copy signage on their highways. Thus, these states still see many signs in this format. Otherwise these signs are, for the most part, phased out in favor of reflective signage.

  • Bypass Route - a bypass route, such as a freeway around a city or town, may be shown with the "BYPASS," "BY-PASS," or "BYP" designation. U.S. and state routes both use bypass routes in select states.

  • Cable-Stayed Bridge - a cable-stayed bridge features cables that connect directly to the mast, pillar, or tower. By comparison, individual suspension bridge cables connect to vertical hangers, and the hangers in turn connect to the tower, mast, or pillar. Examples include the Delaware 1/Relief Route bridge over the Chesapeake and Delaware Canal and the Interstate 275 Sunshine Skyway Bridge over Tampa Bay.

  • Call Box - a call box is a telephone or communications device located at specific intervals along a highway to connect a motorist in distress with police dispatchers. Call box use has declined somewhat in urban areas with the proliferation of cellular telephones, but they are still very much in use in rural areas where call boxes have been installed. An example of call box may be found on the Interstate 8/San Diego County page near the Pine Valley Creek Bridge.

  • Cantilever Bridge - a cantilever bridge is a bridge supported by a beam that is anchored at one end and unsupported at the other end. This kind of bridge is not commonly constructed today. An example is the Interstate 80 Carquinez Bridge near Vallejo, California.

  • Cat's Eyes - highway reflectors are sometimes referred to as cat's eyes because of the similarity between the reflective nature of the street mounted fixtures and the reflectivity of a cat's eyes when illuminated at night.

  • Caution Signage - caution signage is usually colored yellow with black lettering to warn motorists of specific roadway hazards, including curves in the road, sharp upgrades or downgrades, truck escape ramps, speed advisories, etc.

  • Clinched - a route is considered clinched when a road enthusiast has driven it from one end to the other. The word stems from professional sports where a team "clinches" its division or conference title.

  • Cloverleaf Interchange - a cloverleaf interchange provides unrestricted movements between a freeway and another high-capacity roadway (including another freeway or an expressway). There are eight ramps total in this configuration. In addition to an outside diamond configuration, the cloverleaf interchange also features internal loop ramps so that traffic signals and stop signs are not required. The cloverleaf interchange is so named because the internal connecting ramps look like a cloverleaf from above. Due to the weaving that is required to get between the cloverleaf ramps and main lanes, many cloverleaf interchanges are being replaced with modified cloverleaf interchanges and/or flyover ramps. See Kurumi's Cloverleaf Interchanges for more.

  • Collector/Distributor Lane - A collector/distributor lane on a freeway handles entering and exiting traffic. Usually, this lane will begin as an entrance-only ramp initially, but it will sometimes become a main lane or possibly an exit-only lane. The purpose of this lane is to facilitate traffic to the freeway exits and from the freeway entrances.

  • Connector Route - a designation the state of Georgia applies to certain state highways. These state highways basically connect one to another and see "CONN" included within the highway shield design.

  • Construction Signage - construction signage is usually colored orange with black lettering to identify areas of road construction or changed road conditions as a result of an ongoing construction project.

  • Control City - the control city is the city listed on guide signs as the control point. For Interstate Highways, the Federal Highway Administration maintains a list of control cities to be used on freeway signs. The control city may or may not be the next destination of consequence (see destination city).

  • Control Point - a destination on guide signage that is not a town or city. A control point can be a landmark, geographical area, park or other recreational facility, or even an entire state.

  • Controlled Access - a controlled access roadway is one with access points only at interchanges. Normally controlled access highways are freeways.

  • County Highway - a routed highway that is maintained at the county level. These roads are signed with a yellow text on purple background pentagon shield. However, several states maintain their own style of county signage.

  • Decommission - a route is considered decommissioned when signage for that route is removed from the roadway. Decommissioning normally occurs when a route is taken from state control and given to a local entity (city or county) to maintain.

  • Dedicated-Use Lane - a lane that is restricted in its use. Usually this would include lanes for public transit systems, high-occupancy vehicles, or other special classifications of vehicles.

  • Department of Transportation - each state has its own department of transportation that manages its system of highways and roadways. A complete list is available at the Highway Kick-Off Page.

  • Destination City - on mileage signs and overhead guide signs, the destination city is the next city of consequence listed.

  • Diamond Interchange - this is the most basic interchange design, and it consists of four ramps (two offramps and two onramps). Diamond interchanges have a diamond shape when viewed from the air, hence the name. There are four ramps total in this configuration. Traffic exiting a freeway at a diamond interchange will see usually see a stop sign or traffic light to manage traffic leading onto the connecting road. These kinds of interchanges are usually reserved for lower-volume arrangements. See Kurumi's Diamond Interchanges for more.

  • Diamond/Cloverleaf Interchange - some interchanges utilize features of both a diamond and a cloverleaf interchange, perhaps with only four or six ramps. These interchanges may feature one or more loop ramps as well as diamond ramps, and they might be used in cases where real estate for the interchange is limited or when there is significantly higher traffic volume in one direction over another. See Kurumi's Diamond/Cloverlead Interchanges for more.

  • Divided Highway - any highway with a physical barrier (such as jersey barrier or landscaped median) that separates the two directions of traffic is known as a divided highway. Divided highways may have four or more lanes. Divided Highways is also the name of a book and PBS series from 1996 that provided a glimpse of the politics and history behind the development of the nation's highway system.

  • Draw Bridge - a draw bridge is a bridge that has a deck that lifts upward to allow for ships to pass by without overhead obstruction. An example is Interstate 280 over the Maumee River in Toledo, Ohio.

  • Dual Freeway - a dual freeway is when a physical barrier separates express and local traffic so that local, merging traffic is kept separate from through, express traffic. An example of a dual freeway is along the Dan Ryan Expressway (Interstates 90/94) in Chicago, Illinois.

  • Duplex - a duplex is where two routes overlap on the same stretch of pavement.

  • Exit Numbers - interchanges in all states are numbered to reduce motorist confusion and to enable motorists to determine distances between exits within a state. Normally, one of two exit numbering methodologies is used: mileage-based or sequential. Mileage-based exit numbering systems have exit numbers that correspond to the nearest milepost, with the zero milepost normally at the southern or western end of the route. Sequential exit numbering simply starts with exit one and counts upward in a northerly or easterly direction. The mileage-based numbering system is considered preferred since it allows motorists to easily calculate the distance between two exits by calculating the difference between the two exits. If more than one exit is within the same milepost zone, then the exits are identified by letter suffixes (A, B, C, etc.), with the lowest letter (A) being applied to the exit that is the furthest to the west or south. Some states used to use geographical lettering patterns, such as E/W or N/S to identify specific exits, but that convention is rarely seen anymore except in the Northeast.

  • Exit-Only Lane - any lane that is forcibly exiting the freeway is known as an exit-only lane. Normally, signage will indicate that motorists in that lane must exit, sometimes on overhead guide signs with yellow and black tabs, and other times with white guide signs mounted on the side of the freeway.

  • Expressway - an expressway is a limited access, divided highway. Limited access means that there are no driveways or minor streets that intersect the highway, but access may be achieved at spaced traffic lights, interchanges, or stop signs. In some cities, such as Chicago, "expressway" is used synonymously with a road built to full freeway standards.

  • Federal Highway Administration (FHWA) - the Federal Highway Administration (FHWA) is the branch of the federal Department of Transportation that oversees highways in the United States. Generally, the FHWA works with state departments of transportation to carry out federal initiatives, but funding is frequently an issue.

  • Freeway - a freeway is an access-controlled, divided highway. Most freeways are four lanes, or two lanes each direction, but many freeways widen to incorporate more lanes as they enter urban areas. Access is controlled through the use of interchanges, and the type of interchange depends upon the kind of intersecting roadway (surface street, rural road, another freeway, urban arterial, etc.).

  • Freeway Entrance - a freeway entrance is the place where cars may access the access-controlled highway. Usually marked by guide signage (including shields, guide signs, and freeway entrance markers), certain kinds of vehicles (such as bicycles) and pedestrians may be prohibited from entry.

  • Future Interstate Corridor - due to the high priority corridor system, some corridors have been identified as future interstate highway corridors. These corridors are not to receive an Interstate designation until they meet Interstate construction standards.

  • Gantry - a gantry is a road enthusiast term for an overhead structure on a freeway or expressway that carries guide signs. In highway engineering, this structure is known as a sign bridge.

  • Ghost Ramp - a ghost ramp is ramp that leads to nowhere. It may have been constructed originally to connect to another highway, but that connection was never completed.

  • Great Decommissioning of 1964 - in 1964, the state of California decided to eliminate or curtail most of the U.S. routes within its borders. This action was intended to reduce route-numbering confusion for U.S. routes parallel to new Interstate highway corridors, but it also resulted in the creation of several lengthy state routes that replaced the original U.S. routes. Some of the routes eliminated in 1964 were U.S. 40, 60, 66, 70, 80, 91, 99, 101A, 399, and 466. Other routes, such as U.S. 50, 101, and 395 were curtailed in length. Remnants of these routes include today's California 60 (U.S. 60), California 86 (old U.S. 99), California 91 (U.S. 91), California 99 (old U.S. 99), Interstate 10 (old U.S. 60-70), and Interstate 40 (old U.S. 66).

  • Great Recommissioning of 1935/1936 - in 1935-1936, most of the U.S. routes within the state of Wyoming were renumbered to allow for more route continuity and to eliminate shorter routes entirely within the state's boundary. This resulted in the elimination of U.S. 87E, 87W, 116, 185, 216, and 420.

  • Great Renumbering of 1982 - in the mid-1980s, Nevada renumbered all of its state routes to a clustering system whereby similarly numbered routes would be clustered within a county or city.

  • Gousha Road Atlas - the last Gousha Road Atlas was published in 1996 before Rand McNally bought it. For years prior, Gousha was commonly used for many oil company road maps in addition to its own collection of maps and road atlases.

  • Guide Signage - freeway guide signage is usually colored green with white lettering, and it provides route information, roadway names, and names of cities that are accessible by that exit.

  • High Occupancy Vehicle Lane - also known as carpool lanes, high occupancy vehicle (HOV) lanes are lanes reserved for vehicles with two or more occupants. Usually, the HOV Lane is the far left lane, and jersey barriers or other forms of access control may separate the HOV Lane from the main lanes.

  • Hazmat - short for the words "hazardous materials", hazmat related signs usually pertain to truck restrictions through tunnels or a heavily populated area where a hazmat related accident or spill would be detrimental to the immediate surroundings. Shields are in place now for hazmat preferred routes and banned routes. The signage is a white square with the letters HC in a green circle. When this logo is surrounded with a red circle and slash through it, that means that hazmat related traffic is banned from using that particular route.

  • High Priority Corridor - a high priority corridor is a highway or other surface transportation route that has been marked for upgrades or improvements. In some cases, these improvements may result in the creation of a new Interstate highway. The first high priority corridors were identified in 1991, and more routes have been added since then. It is expected that more modifications and additions to the High Priority Corridors will be coming with the transportation reauthorization bill in 2003.

  • High Occupany Vehicle (HOV) - In an effort to ease traffic density, some metropolitan areas or states have implemented HOV lanes or constructed HOV roadways. These stretches of highway are generally restricted in use to vehicles with two or more passengers. In most locales, these restrictions only apply during the peak hours of traffic. However in some cities, the HOV restriction is in place 24 hours. Variable message signs will indicate the restriction times and changes. Interstate 66 between Washington D.C. and the Capital Beltway was once completed signed as HOV-3. That means that anyone driving on any lane of the Interstate with less than three passengers (driver include) would be in violation.

  • Interchange - an interchange is the junction of a freeway and another road. To provide access control, interchanges keep the traffic flowing on the freeway, but there may be some restrictions on the connecting routes. A complete interchange provides for movements in all directions; a partial interchange has some missing connections. There are a wide variety of interchanges, including cloverleads, stacks, single point urban, and trumpets.

  • Intermodal Surface Transportation Efficiency Act of 1991 - this congressional act created the national high priority corridor system and expanded transportation funding to include roads, transit, and other forms of surface transportation such as railroads.

  • Interstate Highway System - the National System of Defense and Interstate Highways was created in 1956 in concept as a system of superhighways that would connect all major metropolitan areas. Much of the system as originally conceived has been completed, and much work today is devoted to maintaining and upgrading the existing system. However, as population has increased, the need for additional high-capacity routes has resulted in additions to the network. Many of these routes, such as the Interstate 69 extension and the new Interstate 73/74 corridor, are identified as high-priority corridors by Congress through the series of surface transportation acts passed during the 1990s and 2000s.

  • Jersey Barrier - a jersey barrier is a concrete barrier that acts as a traffic control device to separate traffic flow.

  • Junction - a junction is a meeting of two highways. Normally, signage will show the approaching route shield and the abbreviation "JCT" on a banner above the route shield.

  • Jughandle - a highway intersection that results in all turns from the right-hand side of the road. The intersection when viewed from above resembles a jughandle in that all left-hand turning traffic exits to the right and loops back to the main road in a perpendicular fashion. This configuration eliminates the need for left-hand turning lanes and signals. The state of New Jersey is well known for its use of jughandle intersections.

  • Level of Service (LOS) - the level of service is a mechanism used by highway departments to determine if a road is operating at ideal, average, or poor efficiency. Termed level of service, each highway is given a grade from A to F that indicates how well the roadway is serving its intended traffic. Roads with a level of service "F" are generally the ones with major traffic issues and are generally prioritized for improvements and innovations to make the roadway better.

  • License Plate - a license plate is a marker affixed to the back, and sometimes also the front, of a vehicle to verify that the vehicle is registered in a state. A wide variety of designs for license plates exist in each state.

  • Lift Bridge - a draw bridge where the deck of the bridge lifts vertically in one segment, instead of at an angle in two segments. For the most part, lift bridges still only exist along railroad corridors and not along highways, but an example is the Heim Bridge along California 47 in Los Angeles, California.

  • Limited Access - a limited access highway is one that has some restrictions on accessing the highway, but it is not fully access controlled like a freeway is.
  • Loop Route - a loop route is a Three-Digit Interstate highway with an even prefix that loops around a city or urban area, including most beltways.

  • Lost Highway - a lost highway is either an abandoned or underutilized stretch of highway that has been bypassed by another, more modern highway. These artifacts are profiled on our Lost Highway page.

  • Main Lanes - all through-traffic lanes that do not exit and are not dedicated-use lanes are considered main lanes. This is sometimes referred to as the mainline of a freeway or highway on AARoads.

  • Main Line - the main line is the main route of a highway. Alternate, business, and bypass routes are considered auxiliaries of the mainline.

  • Manual on Uniform Traffic Control Devices (MUTCD) - the Manual on Uniform Traffic Control Devices governs the use and placement of all traffic control devices, including signs, traffic signals, and median barriers. This manual is the document used by most departments of transportation across the country. Some addenda have been incorporated in specific states, but most states generally follow the rules within the MUTCD.

  • Mapquest.com Road Atlas - the Mapquest.com Atlas is a competitor to the long-running Rand McNally Road Atlas. It was published under the National Geographic Atlas banner between 1998 and 2001, and the Mapquest.com standard map is currently (2003) published within the Mapquest.com Road Atlas, Michelin Road Atlas, American Map Company, and the Barnes & Noble Road Atlas.

  • Mast Arm Traffic Light Assembly - these traffic light assemblies are more wind resistant and more expensive than their span wire assembly counterparts. Mast arm assemblies involve traffic lights supported by a metal pole and mast arm. Western states use these exclusively because of their durability to withstand an earthquake.

  • Median - a median is a barrier, constructed of concrete, asphalt, or landscaping, that separates two directions of traffic.

  • Mileage Sign (Distance Sign) - a mileage sign provides the distance to the next destination city as well as the next control city within rural areas. In urban areas, these signs provide the distance to the next two or three exits. This kind of signage is also referred to as an upcoming exits sign on AARoads.

  • Milepost - a milepost, or milemarker, is a green paddle placed alongside roads and highways that indicate the total mileage from a certain control point. For Interstate routes, the zero milepost is generally at the southern or western end of the route. For all other routes, the location of the zero milepost may vary.

  • Misc.Transport.Road - Misc.transport.road is a Usenet newsgroup that is designed for discussions of roads and related topics. Everything from level of service to highway construction to a philosophical discussion on Interstate 99 may be found at this newsgroup. An archive is available at Google.com.

  • Modified Cloverleaf Interchange - a modified cloverleaf retains the same features as a regular cloverleaf interchange, except that the weaving process is lessened by the use of a collector/distributor lane to reach the cloverleaf. The collector/distributor lane carries much less traffic than the main lanes, so traffic delays as a result of weaving are lessened as a result.

  • Motorist Aid/Service Signage - motorist aid signage is usually colored blue with white lettering, and it provides information to motorists, including rest areas, tourist information centers, motorist aid call boxes, weigh stations, traffic information, and roadside services (such as gas, food, lodging, and attractions).

  • Multiplex - a multiplex is where two or more routes overlap on the same stretch of pavement; sometimes a dually signed road is referred to as a duplex and three routes that share the same stretch of pavement are referred to as a triplex. The FHWA prefers the term overlap in these instances.

  • National Highway System - The National Highway System was designated in 1995 for all roads that are of national importance. Generally, this includes all Interstate routes and some U.S. and state routes. See National Highway System for more information and a map.

  • Neutered Shield - the original interstate shield specifications called for the state name to be included within the shield between the red area and the highway number. However, as the specifications were refined, the state name was removed from the Interstate Shield design. Some states have adopted these later specifications, while others have retained the state name. Those shields that do not carry the state name are referred to as "neutered shields" on AARoads.

  • New England "Y" Interchange - a New England "Y" interchange is another way of terminating one freeway at another freeway, and it features no loop ramps and two bridges rather than just one. Normally, this configuration features a left exit, which is not good for traffic control due to the fact that the left lane (number one lane) is the fast lane and is not a good place for accelerating or decelerating traffic. It is a common kind of interchange in the Northeastern United States, hence the name. See Kurumi's Trumpet Interchanges for more.

  • Not In My Back Yard (NIMBY) - sometimes, property owners along or close to a proposed new highway facility decide that they do not want the freeway in their area. These owners may organize an effort to prevent land acquisition or construction of a freeway or highway, and oftentimes, these local efforts are successful. This has made highway construction in urbanized areas very difficult.

  • Number One Lane - the left lane of the freeway is known as the "number one lane" or the "fast lane." This lane is reserved for the fastest moving vehicles, and should be used for passing only. The other lanes are numbered from left to right, so the right lane may be the Number Two Lane on a four-lane freeway, but it might be the Number Five Lane on a ten-lane freeway.

  • Old Alignment - an old alignment is an historical routing of a route, either existing or dead. For instance, some old U.S. routes remain as weed-covered paths that do not resemble major highways any more, even though they were at one time significant transportation corridors.

  • Optional Lane - an optional lane is a lane that provides motorists with the option of either continuing straight ahead or exiting. These kinds of lanes are common with two or three-lane exits.

  • Overcrossing - an overcrossing is a road that crosses over a freeway.

  • Overlap - an overlap is where two or more routes share the same piece of pavement (see also duplex and multiplex).

  • Overpass - an overpass is a bridge over a freeway.

  • Postmile Marker - in California, the white paddles that denote the mileage of a state route within a county are known as postmiles. Each postmile marker features the route number, county name abbreviation, and mileage. Postmiles increase from south to north and from west to east. Currently, green mileposts are not used in California, but that might change as exit numbers are installed in that state.

  • Ramp Meters - some ramps are metered with a traffic control device to allow for a steady stream of vehicles to enter the freeway. This may result on back-ups of traffic onto nearby surface streets, but the ramp meters keep traffic flowing on the freeway. Ramp meters are commonly found in urban areas.

  • Rand McNally Road Atlas - the oldest road atlas in the United States, the Rand McNally road atlas was first issued in 1926. This first edition was fraught with errors, because it was based on an older, unimplemented version of the U.S. Highway System. The 1927 edition corrected these errors, and the atlas has been updated every year since then.

  • Reassurance shield - a shield located along the highway mainline that reminds motorists what route they are on and what direction they are driving in.

  • Recommission - a recommissioned highway is one that has changed numbers, street names, or route designations. The actual pavement might remain the same as it was, but it has been given a new name.

  • Recreation Signage - recreation signage is usually colored brown with white lettering, and it identifies any recreational or historical sites accessible by a certain exit.

  • Reflective Sign - a reflective sign is a sign that has retro-reflective sheeting to allow for easy visibility at night under the glare of headlights. Nationally, older, non-reflective signs are being replaced with brighter reflective signs. As a side effect of this transition, many states have begun to turn off sign lights to save on electricity costs since headlights are enough to allow for visibility of the reflective sign.

  • Regulatory Sign - a regulatory sign is a white sign with black lettering that indicates any legal requirements of a certain stretch of highway, including state seat belt laws, speed limits, and other legal advisories.

  • Right of Way (Rights of Way) - the right of way is the land set aside for use as a highway corridor. Rights of way are purchased prior to the construction of a new road, and usually enough extra land is purchased for the purpose of building sound walls, retaining walls, and other mitigation features. Sometimes, rights of way are left vacant after the initial roadway facility is constructed to allow for future highway expansion.

  • Road Enthusiast - a road enthusiast is someone who enjoys taking road trips for the love of the road. In fact, two road enthusiasts maintain AARoads.

  • Secret Route - secret routes can be one of two things: first, a highway may be primarily signed with one designation but also carries another designation. This hidden designation is a secret route, including U.S. routes that silently merge onto an Interstate highway and hidden state route control numbers used by various departments of transportation throughout the country. An example is U.S. 87, which is a secret route alongside Interstate 25 in Colorado because it is unsigned for much of its overlapped route. A second definition of secret route is a route that may be maintained by the state and has a state route number but is not signed as such. An example is the stretch of California 1 near Emma Wood State Beach, which is a state highway but does not carry any state route shields on it.

  • Semi-Directional "T" Interchange - the semi-directional "T" interchange is just like the New England "Y" interchange, except that it does not feature left exits. See Kurumi's Trumpet Interchanges for more.

  • Service Road - a service road, or frontage road, parallels a freeway and provides access to the highway at each interchange. Businesses, such as gas stations, restaurants, and motels, may be located along the service road. On occasion, a service road in rural areas may actually be the original alignment of the highway prior to the construction of the freeway. A service road might be called into service as the main route whenever the main lanes of the freeway are closed for any reason.

  • Shield - a shield is the actual route marker. Shields come in many varieties, but the most common shields are for Interstates, U.S. routes, state routes, and county routes. A uniform standard exists for Interstates, U.S. routes, and most county routes across the country, while state route shields vary by state.

  • Sign Bridge - a sign bridge is any structure that supports overhead guide signs that is independent of a regular roadway bridge.

  • Silently Merged Route - lesser routes that merge onto a freeway are generally signed under the primary route, but sometimes they are not signed. In those instances, the secondary route is considered to have silently merged onto the primary route. An example of this is U.S. 23 in Georgia, which silently merges onto Interstate 985 in Georgia but is not well-signed on the overlapped portions.

  • Single-Point Urban Interchange (SPUI) - A single-point urban interchange (also known as an X interchange or urban diamond interchange) is a variant on the standard diamond interchange, whereby all traffic meets at one single traffic signal in the center of the bridge over the freeway (or underneath the freeway). These interchanges can accommodate more traffic in smaller spaces, hence their appeal in urban areas. For more, see Kurumi's Single-Point Urban Interchanges and Missouri DOT's Introduction to SPUIs.

  • Slip Ramp - a short connector ramp that is generally situated between a freeway mainline and adjacent frontage road. These ramps allow motorists to "slip" from one roadway to another. Slip ramps also exist on freeways that are split between a local and express configuration. One such example of this configuration exists along Interstate 270 in metro Washington, D.C.

  • Split Interstates - there are several Interstates that are discontinuous: Interstates 76, 84, 86, and 88. These routes are split apart, sometimes by hundreds of miles. There is little chance of any of them being connected.

  • Sound Barrier or Wall - a concrete wall that separates a highway from the associated environs to dampen the noise pollution to surrounding areas. These are found in urban areas where a freeway or other highway travels through a residential zone. They also provide a function of security to prevent pedestrians from entering the freeway right-of-way. In some cases, a sound barrier may only consist of a wooden stockade fence. New sound barriers feature a motif that emulates a city's culture or background.

  • Span Wire Traffic Light Assembly - refers to a particular traffic light assembly where the lights themselves are supported by a wire spanning the distance of the roadway width. These are less expensive than their mast arm supported counterparts, but are less wind resistant.

  • Spur Route - a spur route is a route from the mainline highway or freeway into a city or town. An example is Interstate 195 in Florida, which connects Interstate 95 in Miami with the city of Miami Beach.

  • Stack Interchange - when high-speed flyover ramps are incorporated into an interchange, it becomes a stack interchange. These ramps may have one or more lanes, and the ramps will fly over each other to an impressive height. Sometimes these additional ramps are built over an existing cloverleaf interchange, and some movements may still feature loop ramps because lower traffic volumes do not warrant a full flyover ramp. However, at the junction of two roadways with busy connections in all directions, a symmetrical stack interchange is appropriate. A symmetrical stack features no stopping between freeways, and guide signs make it is very easy to find the right path through the interchange. The biggest disadvantage to any kind of stack interchange is the cost and size of a stack interchange. The AARoads icon is the aerial view of a symmetrical stack interchange. See Kurumi's Stack Interchanges for more.

  • Stand-alone Shield - this is another name for a reassurance shield or a shield that is not attached to a guide sign.

  • State Official Map - most states offer some kind of tourist information map, and the state tourism office, the state department of transportation, or a contracted private vendor may produce these maps. Normally, these maps are available at state tourist information centers. The quality of official state maps varies by state, depending upon the entity that created the map.

  • Stub End - this term is applied to a relatively small ghost ramp where the pavement appears to be a stub of the main roadway. Currently the southern end of Interstate 310 in Louisiana and the U.S. 219 western New York freeway see their southern ends with stub ends. The final interchange for both highways see a folded diamond interchange to the north, with a single off-ramp and on-ramp. The mainline roadways continue for a short distance beyond the interchange ramps to end in a stub. These stubs are in place for future extensions of both respective highways, where the mainline may continue southward.

  • Suffixed Routes - both the Interstate and U.S. Highway Systems utilize letter suffixes in locations where a route divides into two alternative routes, and neither route is considered to be the "main" route. These routes are denoted by a letter suffix, usually E/W for east/west or N/S for north/south. Most suffixed routes in the Interstate Highway System have been eliminated, with the exceptions being two splits of Interstate 35E/W in Minneapolis/St. Paul and Dallas/Fort Worth. Prior to 1980, there were many suffixed Interstate routes, including Interstate 5W in California; Interstate 15E in California; Interstate 15W in Idaho; Interstate 35W in Kansas; Interstate 70N/S in Maryland and Pennsylvania/Ohio; Interstate 75E in Florida; Interstate 80N in Idaho/Oregon, Iowa, and Ohio; Interstate 80S in Colorado and Ohio/Pennsylvania; and Interstate 81E in Pennsylvania. All of these routes have since been renumbered to reflect a non-suffixed designation. The U.S. Highway System retains several split routes, especially in the vicinity of Tennessee and North Carolina.

  • Suicide Lanes - the middle turning lanes found on busy arterials in urban areas or passing lanes that may be used by either direction of traffic are known as suicide lanes because both directions of traffic can use them. Motorists should use caution when using suicide lanes. An example is along U.S. 287 in Wyoming just north of the Colorado State Line.

  • Super Two - a Super Two roadway has all the limited access features of an expressway but is only two lanes (one in each direction). A Super Two might have interchanges; an example is the Ridgecrest, California, bypass along U.S. 395.

  • Surface Street - a surface street is any street in an urban area that is not a freeway. This term is frequently used in traffic reports when there are traffic delays on the freeway system. Surface streets may be called street, avenue, boulevard, road, place, and other names.

  • Suspension Bridge - a suspension bridge is a bridge with its deck supported by large cables hung from towers, such as the U.S. 101/Golden Gate Bridge or the Interstate 95 George Washington Bridge.

  • Swing Bridge - a swing bridge is a bridge that can be moved either clockwise or counterclockwise to allow for ship traffic pass by without any overhead obstructions.

  • Thomas Brothers Map Guide - the Thomas Brothers Map Guide is a city map in a book format, eschewing the traditional foldout map standard. It has become a more common format since Rand McNally purchased Thomas Brothers.

  • Three-Digit Interstate - a three-digit interstate or 3di is an Interstate Highway that acts as a loop, bypass, or spur from a main Interstate route (known as a one or two-digit interstate). Three-Digit Interstates that begin with an even number are generally routes around or through cities, and routes that begin with an odd number are generally routes that spur into cities or reach areas not located near the main Interstate. The term "three-digit interstate" was coined by Scott Oglesby, webmaster of the popular Three-Digit Interstates @ Kurumi.com site.

  • Toll Bridge - a toll bridge is a bridge that requires motorists to pay a toll. Examples include the San Francisco Bay Bridge (Interstate 80), George Washington Bridge (Interstate 95), and the Chesapeake Bay Bridge-Tunnel (U.S. 13).

  • Toll Road - a toll road is a highway that requires motorists to pay a toll. Examples include the Alligator Alley (Interstate 75), Indiana Toll Road (Interstates 80 and 90), the Massachusetts Turnpike (Interstate 90), and the New York Thruway (Interstates 87 and 90).

  • Traffic Circle/Roundabout - a traffic circle (or roundabout) is a traffic control system that allows traffic to move through a multi-street intersection continuously around a circular center island median. Traffic circles are very common in Tijuana, Baja California, but they are found sporadically throughout the United States. Sometimes traffic circles feature traffic signals.

  • Trailblazer shield - a trailblazer shield indicates the direction a motorist should take to reach a certain route.

  • Transcontinental - a transcontinental route is a highway that crosses the entire United States from coast to coast. Examples include U.S. 20, U.S. 30, Interstate 10, Interstate 80, and Interstate 90.

  • Transportation Efficiency Act for the 21st Century - also known as TEA-21, the Transportation Efficiency Act for the 21st Century was passed in 1998 as a reauthorization of ISTEA. It is going to reauthorized again in 2003.

  • Truck Route - These are auxiliary routes of a U.S. or state highway that is the preferred (or sometimes mandatory) route for commercial truck traffic. Such restrictions may be imposed because of weight or hazardous material restrictions on the primary route or because of community requested that commercial trucks be routed around their area. An example is Truck U.S. 19 in Pittsburgh, Pennsylvania.

  • Trumpet Interchange - a trumpet interchange is designed to provide for all movements when a freeway or expressway ends at another freeway or expressway. It generally incorporates one loop ramp, two high-speed diamond ramps, and one bridge. See Kurumi's Trumpet Interchanges for more.

  • Tunnel - a tunnel used to carry a roadway through a mountain or under a river instead of around or over those obstacles. Tunnels can be very expensive to construct and maintain due to drilling and ventilation requirements. Generally, most tunnels are located in mountainous or hilly regions, and examples include the Fort Pitt Tunnel (Interstate 279) in Pittsburgh and the Waldo Tunnel (U.S. 101) north of San Francisco.

  • Turnpike - a turnpike is a type of toll road; sometimes, turnpikes carry the state name (such as Delaware Turnpike and the New Jersey Turnpike) or the name of a place or person (such as Indian Nation Turnpike or Will Rogers Turnpike). The term turnpike sees most usage in the eastern states.

  • Undercrossing - an undercrossing is a road that crosses under a freeway.

  • Underpass - an underpass is when the freeway passes over a roadway, river, railroad, canyon, or other feature.

  • U.S. Highway - the U.S. Highway System was created in 1926 to assign a standardized marking system for routes that cross state lines. The route numbering system is designed to be logical, with even-numbered routes traveling east-west and odd-numbered routes traveling north-south. The lowest numbers are in the east and north, and the highest numbers are in the west and south. Although the Interstate Highway System has replaced many U.S. Highways in the West, much of the system is still intact in the Eastern United States. The American Association of State highway and Transportation Officials (AASHTO) is responsible for assigning route numbers to the U.S. Highway System.

  • Variable Message Signage - variable message signs (known as VMS) are electronic signs that can be modified to inform motorists of changing conditions. These are commonly used for identifying traffic accidents, heavy traffic due to commuting, construction projects, and weather conditions. They are usually changed from a control center.

  • Weigh Station - also known as a port of entry or check station, a weigh station is a set of scales located alongside a freeway that verifies that trucks and buses are within the legal weight limit, which varies by state. These weigh stations are commonly located at state lines, but they may be found scattered throughout the highway system within the state.

  • Yellow Book - the Yellow Book is so named due to the color of its cover. Officially known as "General Location of National System of Interstate Highways, Including All Additional Routes at Urban Areas Designated in September, 1955," this book provides the original plan for the Interstate Highway System. The yellow book featured a map of the country along with urban insets to document the location of spur and loop routes.

Page Updated October 5, 2003.