Glossary of Terms

AASHTO - American Association of State Highway and Transportation Officials


Acceleration Lane - The portion of the roadway adjoining the main traveled way consisting of tapers, widened areas, or auxiliary lanes which function as speed change lanes, turning lanes or segments of traffic interchange directions.


American with Disability Act (ADA) - A Federal regulation requiring the implementation of accessibility design criteria for highway elements that affect the accessibility and mobility of disabled individuals.  These include sidewalks, parking lots and buildings at transportation facilities, overpasses and underpasses.


Arterials - Functionally classified highway that is characterized by a high degree of continuity and a capacity to quickly move relatively large volumes of traffic but often provide limited access to abutting properties.  The arterial system typically provides for high travel speeds and the longest trip movements.


Auxiliary Lane - The portion of the roadway adjoining the through traveled way fir purposes supplementary to through traffic movement including parking, speed change, turning, storage for turning, weaving or truck climbing.


Average Annual Daily Traffic (AADT) - The total volume of traffic passing a point or segment of a highway facility, in both directions, for one year, divided by the number of days in the year.


Average Daily Traffic (ADT) - A general unit of measure for traffic expressed as the total volume during a given time period, greater than one day and less that one year, divided by the number of days in that time period.


Bicycle Lane - A portion of a roadway, which has been designated by striping, signing and pavement markings for the exclusive use of bicyclists.


Bicycle Path - A bikeway physically separated from motorized vehicular traffic by an open space or barrier.


Capacity - The maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic and control conditions.  Capacity is usually expressed as vehicles per hour or persons per hour.


Categorical Exclusion (CE) - A category of actions that do not individually or cumulatively have a significant effect on the human environment for which, therefore, neither an Environmental Assessment nor an Environmental Impact Statement is required.


Conceptual drawing - An idea that is drawn over an aerial photo of a project area to give an overview of the project and its footprint usually used for presentation purposes. A conceptual drawing does not show the exact limits of a project.  A concept drawing of a project does not necessarily mean that is the way it will be designed or that it will be designed.


Cross Section - A graphical representation of a transverse section of the roadway showing existing ground, roadway template, right of way line and all structures normally plotted at 50-foot intervals on curves and 100-foot intervals (i.e., tangent sections) plotted to scale.


Culvert - A structure that is usually a closed conduit designed hydraulically to take advantage of submergence to increase hydraulic capacity and convey surface runoff through a highway or railroad embankment.  AASHTO classifies a culvert as a structure less than 20-foot span as measured along the roadway centerline.  A culvert is a structure, as distinguished from a bridge, that is usually covered with embankment and is composed of structural material around the entire perimeter.


Curb - A raised or vertical element to provide drainage control, pavement edge delineation, right of way reduction, aesthetics, delineation of pedestrian walkways, reduction of maintenance operations and assistance in orderly roadside development.


Curb and Gutter - A curb element combination with a gutter section to provide an improved longitude drainage system.


Deceleration Lane - The portion of the roadway adjoining the main traveled way consisting of tapers, widened areas, or auxiliary lanes which function as speed change lanes, turning lanes or segments of traffic interchanged directions.


Dedicated Right of Way - Property conveyed to a public-governmental entity, by a private source, for public use and benefit.  For the dedicated property to be valid, a public body must accept the property.


Design Hourly Volume (DHV) - The 30th highest hourly volume of the future year traffic assigned for the design, expressed in vehicles per hour.


Design Speed - The maximum safe speed that can be maintained over a specified section of highway.


Design Vehicle - The vehicle used to design turning radii, off-tracking characteristics, pavement designs, etc.


Design Year - The year for which design hourly volumes are derived to determine the design features required for the proposed improvements, usually 20 years from the date of construction completion.


Eminent Domain - The right of a government to obtain private property for public use by virtue of the superior dominion of the government over all lands within its jurisdiction.


Encroachment - Items placed within the existing right of way by persons other than the Department's staff or authorized agents.


Environmental Assessment (EA) - A concise public document, for which a Federal agency is responsible, that serves to briefly provide sufficient evidence and analyses for determining whether to prepare an Environmental Impact Statement or a Finding of No Signification Impact.


Environmental Impact Statement (EIS) - A detailed written statement, prepared for major Federal actions significantly affecting the quality of the human environment, which discusses the environmental impact of the proposed action; any adverse environmental effects which cannot be avoided should the proposal be implemented; alternatives to the proposed action; the relationship between local short-term uses of man's environment and the maintenance and enhancement of long-term productivity; and any irreversible and irretrievable commitments of resources that would by involved in the proposed action should it be implemented.


Erosion Control - The mitigation measures used to reduce (or decelerate) erosion, which is a natural or geologic process whereby soil materials are detached and transported from one location and deposited elsewhere, primarily due to rainfall, runoff and wind.


FHWA - Federal Highway Administration


Finding of No Significant Impact (FONSI) - A document by a Federal agency briefly presenting the reasons why an action, not otherwise excluded, will not have a significant impact on the human environment and for which an Environmental Impact Statement therefore will not be prepared.


Fiscal Year (FY) - the year starts is July of current year and ends in July of the following year.


Fly-over - A grade separation structure used to accommodate a major left-turning movement.


Freeway - The highest level of arterial.  This facility is characterized by full control of access, high design speeds and high level of driver comfort and safety.


Free-flow - A flow of traffic unaffected by upstream or downstream conditions.


Grade - The rate of slope expressed as a percent between two adjacent Vertical Points of Intersection (VPI).  The numerical value for the grade is the vertical rise or fall in feet for each foot of horizontal distance.  The numerical value is multiplied by 100 and is expressed as a percent.  Upgrades in the direction of stationing are identified as positive (+).  Downgrades are identified as negatives (-).


Gutter - The paved area adjacent to a curb or flume formed in asphalt pavement, used for longitudinal pavement drainage.


Highway, Street or Road - A general term denoting a public way for purposes of vehicular travel, including the entire area within the right of way. (Recommended usage: in urban areas - highway or street, in rural areas - highway or road).


Highway Capacity - The existing and design year (normally 20 years from the end of the proposed construction) traffic volumes are used with the highway capacity calculations to determine the highway design on the desired level of service.


Hydrology - The science that explores the interrelationship between water on the earth and in the atmosphere.  In hydraulic practice for highways, hydrology is used to calculate discharges for a given site based on the site characteristics.


Interchange - A system of ramps in conjunction with one or more grade separations, providing for the movement of traffic between two or more roadways on different levels.


Intersection - The general area where two or more highways join or cross, within which are included the roadway and roadside facilities for traffic movements in that area.


Intersection Sight Distance (ISD) - The sight distance required within the corners of intersections to safely allow a variety of vehicular access or crossing maneuvers based on the type of traffic control at the intersection.


Level of Service (LOS) - A set of criteria that describes the degree to which an intersection, roadway, weaving section or ramp can effectively serve peak-hour and/or daily traffic.


Loop ramp - The free flow loop consists of compounded circular arcs that turn through approximately 270 degrees. This is a standard component of the cloverleaf interchange.


MUTCD - Manual on Uniform Traffic Control Devices


National Environmental Policy Act (NEPA) - NEPA, as amended, is a Federal environmental statute that  requires the consideration of environmental factors through a systematic, interdisciplinary approach before committing to a course of action, the procedures are set forth in CEQ regulations and 23 CFR Part 771.


National Pollutant Discharge Elimination System (NPDES) - Areas determined at risk for erosion due to the construction of a highway facility.  It requires the construction and maintenance of erosion control items during construction.  All NPDES areas to be maintained after completion of a project are to be secured by permanent right or way.


National Register of Historic Places - The National Register is a database of properties that are considered historic and otherwise preserved by Section 106 historic preservation regulations.  The Secretary of the US Department of the Interior maintains and establishes the criteria by which properties are evaluated for the National Register of Historic Places.


Overpass - A grade separation where the subject highway passes over an intersecting highway or railroad.


Queue - A line of vehicles, bicycles, or persons waiting to be served by the system in which the flow rate from the front of the queue determines the average speed within the queue. 


Posted Speed - The maximum legal speed permitted along a given section of highway.


Resurfacing- is the placement of new asphalt pavement on an existing road and is typically performed on roads which show wear such as rutting, pot-holes, cracking, and general failure of the asphalt riding surface.   This process improves the safety of the road to the traveling public and extends the life of the existing and new pavement structure.


Right of Way - The land secured and reserved for the construction and maintenance of a highway/road, sidewalk/bike path and drainage features.


Roundabout - An unsignalized intersection with a circulatory roadway around a central island with all entering vehicles yielding to the circulating traffic.


Shoulder - The portion of the roadway contiguous to the traveled way for the accommodation of stopped vehicles, for emergency use, and for lateral support of base and surface courses.  On sections with curb and gutter, the shoulder extends to the gutter line.


Sidewalk - The portion of the highway section constructed for the use of pedestrians used in combination with curb and gutter.


Spread - The transverse encroachment of stormwater onto a street where flow has accumulated in and next to the roadway gutter.  This water may represent an interruption to traffic flow, splash-related problems and a source of hydroplaning during rainstorms.


State Highway - Any public highway planned, laid out, altered, constructed, reconstructed, improved, repaired, maintained or abandoned by the South Carolina Department of Transportation.


Stopping Sight Distance - The available sight distance on a roadway that is sufficiently long to enable a vehicle traveling at or near the design speed to stop before reaching a stationary object.


Superelevation (e) - The amount of cross slope or "bank" provided on a horizontal curve to counterbalance, in combination with the side friction, the centrifugal force of a vehicle traversing the curve.


Traffic Control Device - Pavement markings, delineation devices regulatory/warning/ route guidance signing and traffic signals to provide a motorist guidance, navigation information and warning.


Traveled way - The portion of the roadway for the movement of vehicles, exclusive of shoulders and auxiliary lanes.


Turn Lane - An auxiliary lane adjoining the through traveled way for speed change, storage and turning.


Two-Way, Left-Turn Lane (TWLTL) - A lane in the median area that extends continuously along a street or highway and is marked to provide a deceleration and storage area, out of the through traffic stream, for vehicles traveling in either direction to use in making left turns.


Underpass - A grade separation where the subject highway passes under an intersecting highway or railroad.


Urban Areas - Those places within boundaries set by the responsible State and local officials having a population of 5000 or more.


Utility Coordination - During the preconstruction stage the utility coordinator will meet with water, electric, gas, telephone, sanitation sewer and cable companies to determine the possible utility impacts to the proposed roadway design.  The utility coordinator acts as a mediator between the design consultant and the utility companies to determine the best design to reduce or eliminate utility conflicts with the roadway.  If a conflict can not be avoided the utility owner will be required to relocate or adjust the facilities before or during the roadway construction activities.


Valley Gutter - A paved longitudinal element placed at the roadway edge to control drainage. 


Value Engineering - A concept that encourages the design of cost effective projects and may include the substitution of alternative designs, materials and/or innovative construction methods.


Warrant - The criteria by which the need for a safety treatment or improvement can be determined.


Weaving - The vehicular maneuvers where the pattern of traffic entering and leaving a highway segment at contiguous points of access results in vehicle paths crossing each other.


Wetlands - Area inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.  Wetlands generally include swamps, marshes, bogs and similar areas.