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G



gap acceptance
The decision by a driver that there is sufficient time and/or distance ahead of an approaching vehicle to allow safe performance of a desired crossing or merging maneuver.
gap judgments
The judgment of a driver of the time and/or distance ahead of an approaching vehicle traveling in a lane that the driver wishes to turn across or merge into.
gap search and acceptance (GSA) zone
Used with interchange/ramp entry traffic models, it is the zone in which the driver searches, evaluates and accepts or rejects the available lags or gaps in the traffic stream for execution of a merging maneuver.
General Accountability Office (GAO)
Conducts analysis of federal programs.
general aviation airport
An airport that serves corporate aviation, flight schools, air charter operations, light cargo or private pilots flying for business or recreation.
girder
A main support member for the bridge structure that usually receives loads from floor beams and stringers; also, any large beam, especially if built up.
geographic information system (GIS)
Computerized mapping and planning tool.
global positioning system (GPS)
A navigation system that uses satellites to provide a receiver on earth with extremely accurate measurements of its three-dimensional position, velocity and time.
grade
The slope (ratio of change in elevation to change in distance) of a roadway typically given in percent; for example, a 2 percent grade represents 2 feet of elevation change over a 100-foot distance.
grade crossing
The point at which a roadway intersects a rail line.
"Green Book"
The official title of this book is: "A Policy on Geometric Design of Highways and Streets." This book is published by AASHTO and contains accepted practices for designing the physical features of a roadway. Examples of these features are sight distance, design speeds, lane width, horizontal and vertical curves, etc.
gross ton-mile
The movement of the combined weight of railroad cars and their contents a distance of one mile.
gross tonnage
The overall volume of a ship's hull, including crew cabins, storerooms and machinery spaces; a ton equals 100 cubic feet.
guardrail
Protective barrier along a roadway to prevent vehicles from leaving the roadway or crossing the centerline.