AARoads Glossary

Cataloged below are many of the terms and phrases used throughout AARoads and in highway discussion overall. The nomenclature does vary among the different departments of transportation charged with maintaining roads and highways across the United States. While certainly not a comprehensive list, modernization of roads and the implementation of electronic toll technology continues to evolve words commonly used by news sites, social media and road enthusiasts alike. Feel free to connect with us via email or social media if we omitted something or should expand this list further.


  • 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.

  • Arrow Per Lane (APL) Sign - formally referred to as an Overhead Arrow Per Lane (OAPL) sign, these signs were added to the 2009 MUTCD for use on multi lane highways where an optional exit lane is present. The signs are not new to highway systems worldwide, as European Motorways have incorporated them for years prior.

  • Adopt-A-Highway Program - Sometimes segments of highway might be "adopted" by a local organization, a business or an individual as a community service. The organization members pick up trash and clean up the rights of way along the highway.

  • Agricultural Inspection Stations - Within California, agricultural inspection stations operate by 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.
    Florida is another state that utilizes these stations, but only trucks, including rentals, are required to enter the facilities.

  • All Electronic Tolling (AET) - AET refers to a toll road or managed lane that collects all fees electronically through either a transponder system or toll-by-plate system. There are no conventional toll booths or cash collection of any kind on these facilities. Transponder systems vary across the country, with Fastrak used by California, TxTag and others in Texas, Sunpass in Florida and E-ZPass spread across Midwestern and Northeastern states among many more.

  • Alternate Route - 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. These routes accommodate four or more lanes of traffic and are often lined with businesses or private driveways.

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

  • Auxiliary (Supplemental) 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. Counts are usually classified as vehicles per day (vpd). 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, bypass or truck 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 Shield - A roadgeek specific term, 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 generally a surface street route that leads into a downtown or 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 of an Interstate highway with green and white shields. 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 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. These signs are, for the most part, phased out in favor of reflective signage and becoming fewer in number.

  • 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. Bypass routes are not necessarily limited or controlled access routes. At-grade bypasses often represent the main commercial corridors for smaller cities, such as Jackson, Tennessee.

  • 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 / William Roth 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 declined significantly with the proliferation of cellular telephones, leading to their removal across the majority of the country. Some remain in use in remote areas or on select bridges such as the Sunshine Skyway over Tampa Bay.

  • Cantilever Bridge - A cantilever bridge is a span 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 eastbound 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.

  • Center Turn Lanes - The middle turning lanes found on busy arterials in urban areas or passing lanes that may be used by either direction of traffic. Sometimes these lanes are nicknamed as suicide lanes because both directions of traffic can use them. An example is along U.S. 287 in Wyoming just north of the Colorado State Line.

  • 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 four-leaf clover from above. Due to the weaving that is required to get between the loop ramps and main lanes, many cloverleaf interchanges have been replaced with single point urban interchanges (SPUI), diverging diamond interchanges (DDI) or parclo interchanges where two of the loop ramps are simply removed. See Kurumi's Cloverleaf Interchanges for more.

  • Cloverstack Interchange - An interchange between two high-speed routes where two of the cloverleaf ramps are replaced with directional ramps, generally in a stacked orientation.

  • Collector Distributor Roadway - A collector distributor (c/d) roadway on a freeway handles entering and exiting traffic at a single interchange of through a group of adjacent interchanges. These lanes separate on and off-ramp movements from a freeway or expressway mainline to reduce motorist weaving on through traffic. C/d roadways are also often used at full cloverleaf interchanges, allowing them to remain in place due to the reduced weaving traffic.

  • Community Interchanges Identification Sign - Signs listing a series of exits for suburban or rural communities served by two or three interchanges. Exits are listed to the nearest quarter mile, with the community name displayed on the top line. Additional information on their use can be found on page 225 of the 2009 Manual on Uniform Traffic Control Devices (MUTCD).

  • Connector Route - A designation the state of Georgia applies to certain state routes. These highways basically connect one to another and include "CONN" within the highway shield design.
    South Carolina also utilizes Connector routes for both U.S. and state highways, but does not sign these in the field.

  • 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. Fluorescent pink signs are also used for incident management, survey crews, and other more short term road work or traffic pattern changes.

  • Contraflow - A configuration where transportation and government officials will temporarily shift a freeway or other highway into one-way traffic. Generally contraflow options are available along Interstate highways leading away from coastal areas in the Gulf Coast and Southeastern States during hurricane evacuation situations. Contraflow utilizes temporary slip ramps located within a freeway median to dispurse traffic onto both carriageways. A series of barricades close ramps to opposing traffic while folded signs are used at on-ramps repurposed as off-ramps during contraflow.

  • 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. An examples is the use of Delaware Water Gap for Interstate 80 west in New Jersey.

  • Controlled Access - A controlled access roadway is one with access points only at interchanges or intersections. No private driveways or business entrances are permitted on controlled access roadways. These roads are often regarded as expressways, though controlled access arterials exist as well such as Maryland 24 in Harford County.

  • County Road / County Highway - A routed highway that is maintained at the county level. These roads are mostly signed on a pentagon shield with yellow text on blue background. Variations exist such as where Wisconsin uses lettered rectangles for county trunk highways, West Virginia with circle shields for their county routes and Missouri's lettered routes posted on square markers.
    County routes originated in 1958 with the formation of the California County Route Marker Program. Signs were designed to display the county and route number in a blue and gold color scheme for California. Routes were established to mark routes of major importance that were of general public interest, built to sufficient standards and with a logical beginning and end point. The success of the program in California led its adoption as the National Uniform County Route Marker Program by the National Association of Counties (NACO) in 1967. The blue and gold sign style remained the same and continues through today. More on the origins of the County Road pentagon and the source for our description is found here.

  • County State Aid Highway (CSAH) - County level roads in Minnesota that are eligible for funding from the County State Aid Highway Fund. Some variation in signage for CSAH and County Roads in Minnesota may be found where CSAH routes use the standard blue and gold pentagon and County Roads use the white square.

  • Decommissioned - 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 or replaced with a new alignment using a different route number.

  • 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 (DOT) - Each state has its own department of transportation that manages its system of highways and roadways, usually in addition to airports and seaports. Not all agencies use DOT as an acronym. For instance, Arkansas is the Arkansas Highway Departmant (AHTD) and Vermont is the Agceny of Transportation (VTrans). A complete list of all organizations is available at the FHWA web site.

  • 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 off-ramps and two on-ramps). 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. More modern diamond interchanges incorporate roundabouts at the ramp ends. The type of roundabout gives the nickname of a dog bone or dumbbell interchange. See Kurumi's Diamond Interchanges for more.

  • Directional-T Interchange - An interchange where two routes, generally expressways or freeways, come together with directional ramps forming the shape of a T when viewed from above.

  • Diverging Diamond Interchange (DDI) - A new type of interchange appearing throughout the United States starting in 2009 with the opening of the DDI between Interstate 44 and Missouri 13. This interchange sees the carriageways of an intersecting road switch sides above or below the parent freeway, removing the need to clear opposing traffic for all left-hand turn movements.

  • Divided Highway - Any highway with a physical barrier (such as concrete 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.

  • Dog Bone Interchange - A diamond interchange where the ramp ends at the intersecting road meet at incomplete roundabouts. Coupled with the connecting road, these roundabouts from above resemble the shape of a dog bone. This exchange differs only from dumbbell interchanges in that traffic cannot travel 360 degrees around the respective roundabouts.

  • Draw Bridge - A draw bridge is a bridge that has a deck or double leaf bascule 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.

  • Dumbbell Interchange - a diamond interchange where full roundabouts facilitate traffic movements at the ramp ends. The design appears to form a dumbbell when viewed from above.

  • Dynamic Message Sign - an electronic sign with a changeable board displaying travel conditions, travel times or highway safety message along a highway. See also Variable Message Sign.

  • Egress Point - the exit ramp or departure point where motorists may leave a managed lane or reversible roadway. Egress Points are used when lane changes are otherwise prohibited between the general purpose lanes and HOV or tolled express lanes.

  • 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 preferred since it both allows motorists to easily reference the distance between two exits by calculating the difference between the two exits while also not upsetting the preexisting interchange numbers when a new interchange is constructed. 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 implement geographical lettering patterns, such as E/W or N/S to identify specific exits, but that convention is mostly phased out with some exceptions in the Northeast. FHWA mandates that all states use mileage based exit numbers by 2020, so eventually sequential based systems will be of historical nature only.

  • Exit-Only Lane - any lane that is forcibly exiting the freeway may be referred to 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 generally another term for a controlled access, divided highway. Controlled 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 and New York, "expressway" is used synonymously with a road built to full freeway (limited access) standards.

  • Express Lanes - express lanes were originally used for dual freeway segments where the inside carriageways provided limited ingress and egress points, allowing for higher speeds and better traffic flow due to the lack of merging traffic. A six mile segment of Interstate 96 from Livonia to Detroit, Michigan and Interstate 80 through Patterson, New Jersey include examples of this type of express lanes. Express lanes nowadays referred to toll lanes or tolled carriageways incorporated into a toll free freeway. Interstate 595 (Port Everglades Expressway) in Broward County and Interstate 95 east of Baltimore incorporate Express Lanes where motorists may use the high speed lanes for a variable toll rate. Express Lanes differ from High Occupancy Toll (HO/T) lanes in that all motorists are levied a fee regardless of the number of passengers present.
    Projects in 2016 and beyond add Express Lanes to overall toll roads, allowing commuters on the Homestead Extension of Florida's Turnpike, the Beachline Expressway (SR 528) at Orlando and Veterans Expressway (SR 589) at Tampa, Florida to pay a higher rate to bypass the toll road mainlines.

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

  • Flashing Yellow Arrow (FYA) - A vertically orientated four-head signal where the bottom lens flashes with a yellow arrow, indicating that turning traffic may proceed with caution. This type of signal generally replaces "dog house " traffic lights where green and yellow arrow lens are orientated next to green and yellow ball lens. It permits left-hand turns after yields made for opposing traffic and pedestrians.

  • Freeway - a freeway is a limited access divided highway with no at-grade intersections or railroad crossings. Freeways incorporate interchanges for all movements with intersecting roads. Speed limits are generally high (55 miles per hour or more) while pedestrian, farm machinery (with exceptions), and other slow speed traffic such as bicycles and mopeds are prohibited. Shoulders on freeways are reserved for emergency stopping only.

  • Freeway Entrance - a freeway entrance is the place where motorists may access a limited access highway. Some of the Western states, Illinois (in select locations) and West Virginia formally mark the on-ramps to freeways with green "Freeway Entrance" signs. These assemblies are often coupled with a route marker and signs prohibiting pedestrians and bicyclists.

  • Future Interstate Corridor - due to the high priority corridor system and acts of Congress, some routes have been identified as future interstate highway corridors. These corridors are not to receive a formal Interstate designation until they meet Interstate construction standards. They are often signed with sporadically placed green signs touting the route as a Future Interstate.

  • 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.
    The term is also used formally for all electronic toll (AET) collection points, where an array of transponder readers and cameras are used to levy tolls from a metal truss based structure.

  • General Purpose Lanes - the term used for the toll free lanes of a limited access highway that incorporates Express, HOV, or HO/T lanes. For instance, Interstate 95 through Miami-Dade County is 12 lanes wide with four general purpose lanes per direction and four overall SunPass-only HO/T lanes.

  • Geonova Road Atlas - road atlases using the Geonova base were a competitor to the long-running Rand McNally Road Atlas. It was published under the National Geographic Atlas banner between 1998 and 2001, and later as the Mapquest.com Road Atlas, Michelin Road Atlas, American Map Company Atlas, and the Barnes & Noble Road Atlas. The artwork base for these atlases was eventually discontinued.

  • Ghost Ramp - a ghost ramp consists of a closed on or off-ramp that was partially built in anticipation of a future or scuttled highway project or permanently closed due to safety reasons, alignment changes, or to reduce a conflict point.

  • Gore Point the triangular shaped paved (usually painted with chevrons) and grassy area where an off-ramp separates from a freeway or other highway. A gore point sign constitutes a nondescript sign with the word "Exit", a diagonal arrow and usually an exit number.

  • 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 and retired the art work. For years prior, Gousha was commonly used for many oil companies in addition to its own collection of folding 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 concrete barriers, plastic pylons, painted medians 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 prohibited 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, with many more routes added since then.

  • High Occupancy Vehicle (HOV) - In an effort to ease traffic density, some metropolitan areas or states 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 indicate the restriction times and changes. Interstate 66 between Washington D.C. and the Capital Beltway was once completely signed as HOV-4. That meant that anyone driving on any lane of the Interstate with less than four passengers (driver include) would be in violation. Many HOV facilities were converted to High Occupancy Toll (HO/T) or Express toll lanes.

  • High Occupancy Toll Lanes (HOT or HO/T) - these lanes function similar to Express Lanes or conventional HOV lanes on Interstates and other commuter freeways in metropolitan areas. HOV eligible motorists may use these lanes free of charge, either through a preregistered account (such as with Peach Pass in Georgia), with an E-ZPass Flex transponder (such as in Northern Virginia), or simply by having the necessary number of passengers (Fastrak Lanes on I-15 in San Diego). Single occupent motorists are charged a variable rate depending upon time of day and traffic congestion. Tolls are paid electronically through transponders or toll-by-plate technology at AET gantries.

  • Ingress Point - the entry point or access ramp allowing drivers on a freeway general purpose lanes to move onto a managed lane (HOV, HO/T, Express Lane).

  • 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 interchange types.

  • Interchange Sequence Sign - are guide signs that are typically used along urban freeways with closely spaced interchanges. As per Federal guidelines, the installation of these signs is optional. When used, this type of sign should be used over the entire length of a route in an urban area. Signs should also be used in place of Advance Guide signs if there is less than 800 feet between exits. Additional information on their use can be found on page 223 of the 2009 Manual on Uniform Traffic Control Devices (MUTCD).

  • 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 was completed, and much work today involves maintaining and upgrading the existing system. However, as population has increased, the need for additional high-capacity routes resulted in additions to the network. Many of these routes, such as the Interstate 69 extension to the Rio Grande Valley and the Interstates 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. The name was derived from New Jersey, where they were first used.

  • 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. It also may be used to provide a sufficient turning radius for semi truck traffic. The state of New Jersey is well known for its use of jughandle intersections.

  • Lane Control Signal - a set of electronic signs displaying either a green down arrow or a red letter X indicating whether a travel lane is open or closed. These are generally found on major bridges in the Northeast, where lanes may be adjusted during the respective peak hours to allow for an additional lane in one direction at the expense of the other. Additional uses include commuter based arterial routes, such as U.S. 19 through north Atlanta and U.S. 6 (Dodge Street) through Omaha, Nebraska.

  • 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.

  • Lexus Lanes - a nickname given to Express Lanes or HO/T lanes where the general public regards the toll rates as so excessive that only drivers that can afford a luxury vehicle (like a Lexus) can afford to drive on them. This term is used by news and television media routinely when covering stories on Express Lane projects or expansion.

  • License Plate - a license plate is affixed to the front and back of a vehicle to verify that the vehicle is registered in a state. A wide variety of designs for license plates are available in each state to support an array of organizations and charities. 19 states currently only require a rear facing plate.

  • 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.

  • Limited Access - a limited access highway is a freeway where access is only provided at grade separated interchanges. These are high speed routes that are generally restricted to vehicular traffic.

  • 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. Georgia and Texas both incorporates Loops as auxiliary state routees / highways. A prime example is Georgia Loop 10 encircling Athens as a freeway.

  • Main Lanes / Main Line - 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 main line of a freeway or highway on AARoads. The main line is also the main route of a highway. Alternate, business, bypass and truck routes are considered auxiliaries of the main line.

  • Managed Lanes - travel lanes associated with a freeway or arterial controlled by lane control signals, electronic toll collection or gates allowing for reversible operation.

  • 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 FHWA MUTCD.

  • Mast Arm Traffic Light Assembly - these traffic light assemblies are more wind resistant and expensive than their span wire assembly counterparts. Mast arm assemblies support traffic lights on a metal pole and mast. Western states used these historically because of their durability to withstand an earthquake, but now their use extends nationwide.

  • 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 or when leaving an urban area.

  • Milepost - a milepost, or mile marker, 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. California and Nevada use white paddles (postmile markers) referencing the zero milepost at a county line or the starting point of a route.

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

  • 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 c/d lane carries much less traffic than the main lanes, so traffic impacts 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, traffic information, and roadside services (such as gas, food, lodging, and attractions). The signs advertising local businesses are also referred to as "Logo Signs".

  • Multiplex - a multiplex is a roadgeek term 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 utilizes the term overlap in these instances. Additionally some states referenced shared alignments as braided routes.

  • 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 design included the state name between the red area and the highway number. However, as the specifications were refined and number sizes increased, the state name was removed from the Interstate Shield design. Ohio was the first state to formally drop the state name. Other states followed from 1970 onwards. However Louisiana, Mississippi and Texas readopted the state name on Interstate shields after 2009. Those shields that do not carry the state name are sometimes referred to as "neutered shields" on AARoads and by road enthusiasts in general.

  • Not In My Back Yard (NIMBY) - sometimes business or property owners along or close to a proposed new highway facility or future road construction oppose a project due to eminent domain issues, access changes, quality of life reasons or other disruptive impacts. Individuals sometimes organize with others to form citizens groups in an effort to obstruct land acquisition or construction of a freeway or highway. Oftentimes, these local efforts are successful, such as the case with the Citizens to Preserve Overton Park group that halted Interstate 40 construction through Memphis.

  • 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 is the Number Two Lane on a four-lane freeway, and 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. Old alignments may also consist of a frontage road or residential street that was bypassed by a newer or wider alignment later.

  • Open Road Tolling - terminology used by Illinois and Oklahoma to refer to all electronic tolling (AET) operations. Open road tolling refers to paying tolls electronically without having to slow down from freeway speeds or stop at a toll booth.

  • 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. Optional lanes are signed with Overhead Arrow Per Lane (OAPL) signs on expressways and freeways.

  • Over Crossing / Overpass - an over crossing is a bridge that carries a road, railroad, or pedestrian walkway across a freeway or other highway.

  • Overlap - an overlap is where two or more numbered routes share the same alignment. These may also be referred to as a concurrency or cosigned route.

  • Partial Cloverleaf (Parclo) Interchange - some interchanges utilize features of both a diamond and a cloverleaf interchange. These interchanges may feature one or more loop ramps in addition to diamond ramps. 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. Types include the parclo A2, where the loop ramps form on-ramps, parclo B2 where the loop ramps are off-ramps, and parclo B4, which utilizes six ramps with multiple on-ramps but a single off-ramp. See Kurumi's Diamond/Cloverleaf Interchanges for more.

  • 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.

  • Ramp Meters - some on-ramps are governed with a traffic control device to regulate the flow of merging traffic onto a freeway. Ramp meters are commonly found in urban and metropolitan areas and are used to aid in maintaining travel speeds on freeway mainlines. Queues from the ramp signals may result in traffic back ups onto nearby surface streets.

  • 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 indicates both the route traveled upon and cardinal direction. The FHWA MUTCD specifies reassurance markers as shields posted between intersections in urban areas and beyond the built-up area of a municipality. Confirming markers are the shields used beyond junctions with numbered routes, though the term reassurance markers is often used for these assemblies as well.

  • Recommission - a recommissioned highway is one that has changed numbers, street names, or route designations. The roadway might remain unchanged, but it has been given a new name. An example is Interstate 84 through northeastern Connecticut. It was redesignated as I-86 in 1969 but recommissioned as I-84 in 1984.

  • Recreation Signage - recreation signage is usually colored brown with white lettering, and it identifies any recreational or historical sites accessible by a certain exit or roadway. States such as Texas use a separate class of route for parks and recreation areas.

  • Reflective Sign - a reflective sign is a sign that has retro-reflective sheeting to allow for easy visibility at night under the illumination of headlights. Nationally, older, non-reflective signs, including the bulk of button copy based signs, were mostly replaced with highly reflective signs. As a side effect of this transition, many states coupled replacements with the removal of sign lights to offset electricity and maintenance costs as newer reflectivity standards provide ample legibility in low lighting.

  • 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 traffic laws. Stop and yield signs fall under the category of regulatory signs as well.

  • Reversible Roadway - one to three lane carriageways that flow one direction during the morning or inbound commute hours and the opposite during the evening or outbound peak travel times. These are separated from the general travel lanes by a physical barrier, with entry points closed by barricades or movable gates to prevent wrong-way crashes. Interstate 64 in Norfolk and Virginia Beach and the Express Lanes for I-5 in Seattle, Washington both incorporate reversible roadways.

  • Right of Way (Rights of Way) - thhe land set aside for use as a street or highway corridor. Rights of way are purchased prior to the construction of a new road, and usually sufficient extra land is purchased for the purpose of building sound walls, retaining walls, storm water sewer systems 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, photographing highways, collecting road maps and/or clinching routes for the love of the road.

  • Roundabout - a roundabout replaces a conventional intersection managed by traffic signals or stop signs with a one or more lane wide rotary around a center island median. Roundabout construction has accelerated nationwide, especially in neighborhood areas and with new developments. States such as Wisconsin converted a number of intersections to roundabouts to reduce crash rate numbers. The state also uses roundabouts routinely for interchange redesign, implementing the dumbbell and dog bone design in place of conventional diamonds.

  • Unsigned Route - unsigned routes can be one of two things: first, a highway may be primarily signed with one designation (such as a U.S. highway) but also carry another designation (such as a state route). These hidden designations include 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 the unsigned counterpart running alongside Interstate 25 in Colorado.
    A second definition of an unsigned route is a route that may be maintained by the state and has a state route number but is not signed in the field. An example is the stretch of California 1 near Emma Wood State Beach, which is an unmarked state route.

  • Semi-Directional "T" Interchange - the semi-directional "T" interchange is just like the Directional T 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. Texas maintains a far reaching system of service roads along the majority of the freeway system.

  • Shield - a shield is a numbered 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. Other shields found include those for toll roads (turnpikes), parkways, cultural and historic auto trail routes.

  • Sign Bridge - a sign bridge is any structure that supports overhead guide signs independent of an overpass or flyover ramp.

  • Signal Backplate - A traffic signal backplate surrounds a light to help it stand out against the sky or background. An option in the MUTCD allows departments of transportation to add a yellow retroreflective borders. A 1998 study conducted by the Insurance Corp. of British Columbia and the Canadian National Committee on Uniform Traffic Control, investigated the effectiveness of applying retroreflective tape around the borders of traffic signal backplates. The investigation concluded that the enhancement was effective at reducing crashes.
    Following the Canadian study, yellow backplates were installed at three intersections in Columbia, South Carolina. An intersection safety case study revealed that the three locations experienced a 28.6 percent reduction in total crashes during a 25 month period.
    An added benefit is that the retroreflective borders add visibility to signal heads during power outages. This draws extra attention for motorists to treat the dark signals as a four-way stop.
    Source: "Traffic signals on Clairemont Avenue get shiny new look." Leader-Telegram (Eau Claire, WI), December 28, 2013.

  • Single-Point Urban Interchange (SPUI) - A single-point urban interchange (also known as an 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, but require a larger, more expensive bridge structure. For more, see Kurumi's Single-Point Urban Interchanges.

  • Slip Ramp - a short connector ramp that is generally situated between a freeway mainline and adjacent frontage road or c/d roadway. 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 the dual freeway portion of Interstate 270 in Montgomery County, Maryland.

  • 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 and suburban 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. Most new sound barriers feature a motif that reflects a city's culture or history.

  • Span Wire Traffic Light Assembly - refers to a traffic light assembly where the signal 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. Georgia, Arkansas, Missouri, TExas and Virginia sign spur routes for U.S. and/or State Routes as local connectors between a parent route and another roadway or a community. South Carolina also incorporates spur routes, but those are not signed in the field.

  • Stack Interchange - another name for a multi-level interchange where high-speed flyovers cross over one another or another bridge. These ramps may have one or more lanes, and the flyovers may rise over each other to an impressive height. Stack interchanges are generally found in where freeways were built later in less developed areas, where ample right of way was available. California, Arizona and Texas are home to numerous stack interchanges. See Kurumi's Stack Interchanges for more.

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

  • State Highway - term used for a state-maintained road in Arkansas, Colorado, Idaho, Iowa, Kansas, Louisiana, Michigan, Mississippi, Montana, Nebraska, North Carolina, North Dakota, Oklahoma, South Carolina, South Dakota, Texas, Wyoming.

  • State Trunk Highway - term used for a state-maintained road in Wisconsin. Minnesota uses the simpler nomenclature of Trunk Highway. Michigan's state highway network is formally referred to as the State Trunkline Highway System.

  • State Official Map - most states offer some kind of tourist information map, and the state tourism office, the state department of transportation (DOT), or a contracted private vendor may produce these maps. Normally, these maps are available at state tourist information (welcome) centers found near state lines or are available by request on line or as part of a tourist packet. The quality of official state maps varies by state, depending upon the organization that created the map.

  • State Road - term used for a state-maintained road in Florida, Indiana and New Mexico. Indiana uses the term interchangeably with state highway.

  • State Route - term used for a state-maintained road in most of the United States.

  • Stub End - this term is used interchangeably with ghost ramp where the pavement prematurely ends as a stub of the main roadway. The southern terminus of Interstate 310 in Louisiana and the north end of Interstate 990 near Lockport, New York both conclude with stub ends. The final interchanges for both freeways included provisions for once planned extensions.

  • Suffixed Routes - all four route classes utilize letter suffixes in some form across the United States. Cases for suffixed routes include the scenario where a highway divides into two alternative routes and neither route is considered to be the "main" route. U.S. 49E (east) and 49W (west) in Mississippi, where the east branch serves Greenwood and the west branch serves Indianola, is an example of this.
    Another instance occurs along state and county roads when a route separates into multiple segments. Mississippi 9W provides a west branch of SR 9 to Oxford for instance, while three respective branches of Santa Rosa County 191 in Florida are signed as 191A, 191B and 191C.
    Most suffixed routes in the Interstate Highway System were eliminated due to motorist confusion as advocated by AASHTO starting in 1973. Exceptions until 2012 included the two partitions of Interstate 35 at Minneapolis/St. Paul and Dallas/Fort Worth. The Congressionally designated IH 69 corridor in South Texas designated three new suffixed routes.

  • Super Two - a Super Two roadway has the design features of a conventional four-lane expressway or freeway, but with only two lanes separated by striping instead of a median. 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 travels at-grade with intersections and or driveways and business entrances. 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, or an assortment of 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 George Washington Bridge along Interstate 95 across the Hudson River.

  • 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. There are few of these left along vehicular roads, but several remain along railroad lines.

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

  • Three-Digit Interstate (3DI) - 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, who originally cataloged them all at Kurumi.com.

  • Three-Wye Interchange - a high speed interchange joining two routes where ramps come together as a series of three-wye interchanges. This varies from a Directional-T interchange in that the two routes intersecting do not do so at a 90 degree angle.

  • 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).

  • Toll-by-Plate - an electronic collection system were cameras capture imagery of a motorist's vehicle and license plate for the purposes of processing a toll invoice to be mailed to the registrant's address later. These fees are typically higher than transponder based tolls. They alsod include an administration fee.

  • Traffic Circle - a traffic circle 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, and were found throughout New England and the state of New Jersey. These differ from roundabouts in that they are larger radius and usually multi lane in width. Somerville Circle in New Jersey, where U.S. 202, U.S. 206 and NJ 28 come together, is a good example of one.

  • Traffic Light / Signal - a traffic light is a device used to control movements at an intersection or at-grade crossing between two roads. Standard signals use three lens orientated from top to bottom or left to right with red, amber and green. Signals vary in housing styles based upon manufacturer and color schemes from state to state, and in municipalities throughout the country.
    Variations of signals include the five-lens doghouse signal with left or right turn arrows, the four or five signal stacked signals, with amber and yellow turn arrows at the bottom, and upside down T signals with a green arrow positioned along side a green ball lens.
    Backplates are added to signals to add visibility against the sky or background. Visors vary between full tunnel or cutout assemblies.

  • Trailblazer shield - a trailblazer shield indicates the direction a motorist should take to reach a particular route. Trailblazers are often associated with toll roads and Interstate highways.

  • Transponder - an electronic device that processes tolls from a prepaid account. A set of readers at AET gantries and other toll collection communicates with the transponder to automatically deduct fees from motorist's accounts. Transponders are usually referred to as a toll pass or toll tag. There are a number of toll systems in use across the country with some interoperability between agencies. The long term goal is to have all systems interoperable, so that a driver using an E-ZPass from Pennsylvania can drive on a GeauxPass based toll road in Louisiana and vice versa.

  • 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 was reauthorized again in 2003.

  • Truck Route - These are auxiliary routes of a U.S. or state route 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 a 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. When viewed from above, the interchange resembles the musical instrument. See Kurumi's Trumpet Interchanges for more.

  • Tunnel - a tunnel carries a roadway through a mountain or under a river instead of around or over those obstacles. Tunnels are very expensive to construct and maintain due to drilling, ventilation and maintenance 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 [Robin Williams] Tunnel (U.S. 101) north of San Francisco.

  • Turnpike - a road name generally used in the Northeast dating back to original toll roads used for horse and carts and later for mid-20th century superhighways. The name originates from the barrier used at toll booths during the early automobile era. Turnpikes today represent high speed toll highways.

  • Under Crossing / Underpass - an under crossing takes a road, multi use path or railroad under a freeway or other highway

  • U.S. Highway - the U.S. Highway System was created in 1926 to replace the inconsistently marked and maintained auto trail system. It assigned a standardized marking system for routes that crossed state lines. The route numbering system was 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 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 Sign - variable message signs (known as VMS) are electronic signs that can be modified to inform motorists of changing conditions. These are commonly used for displaying travel times to the next exit(s), alerting motorists of forthcoming traffic accidents and congestion, advising the public about ongoing Amber and Silver Alerts, indicating construction related closures and lane shifts and warning of severe weather. They are usually operated by a traffic operations center.

  • Volleyball Interchange - a multilevel interchange where two multi lane highways are connected with intersecting diamond interchanges. Interstate 476 and U.S. 1 at Media, Pennsylvania and Interstate 240 at U.S. 70 at Asheville, North Carolina are two uses of this exchange. Hat tip to Kurumi for the terminology.

  • Weigh Station - also known as a port of entry or check station out west, a weigh station constitutes a set of scales located alongside a freeway that verifies that trucks and buses are within the legal weight limit. Hours of operation and limits vary from state to state. Weigh stations are commonly located near state lines, but they may be found scattered throughout the highway system within the state.

  • Wye Interchange - a partial interchange where two roads come together in the shape of a "Y", with a single on-ramp in one direction and off-ramp in the other. These are generally located where one route splits with another and where reverse access is counter intuitive or accomplished by another connection.

  • 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.

  • Zipper Barrier - a moveable section of concrete barriers used to separate traffic on multi lane highways. Zipper barriers are used along Interstate H1 on Oahu and Interstate 66 across the Potomac River, among other locations. Use of these barriers reallocates a westbound lane for the eastbound / morning commute and vice versa during the evening. A barrier transfer machine moves the barriers.

Page Updated September 11, 2016.

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