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half-diamond interchange
An interchange with a one-way, diagonal-type ramp in two adjacent quadrants; this type of interchange is appropriate to situations in which traffic demand is predominantly in one direction.
hanger
A tension member serving to suspend an attached member on a bridge.
A facility where airplanes are stored.
haulage rights
Rights obtained by one railroad to have its trains operated by another railroad over that railroad's tracks.
high-occupancy vehicle (HOV)
Any passenger vehicle that meets or exceeds a certain, predetermined minimum of passengers, generally two or more.
high-occupancy vehicle lane
A highway or street lane reserved for one or more specified category of vehicle, usually buses, carpools and vanpools.
high-mast lighting
Illumination of a large area by means of a cluster of luminaries, which are designed to be mounted in fixed orientation at the top of a high mast (generally 80 feet or higher).
high-spatial-frequency stimulus
A visual target characterized by fine detail.
highway advisory radio (HAR)
A radio station which broadcasts highway conditions and traffic information.
highway-railroad
The point at which a roadway and railway intersect.
highway sufficiency rating
A 0-100 rating representing the relative condition of the highway segment (0 worst 100 best); this measure takes into account the structural adequacy, safety and service of each segment; the rating is used as a performance measure and as a tool to identify reconstruction needs; per Code of Iowa requirements, department staff calculates ratings annually for all state highway segments.
Highway Trust Fund
The federal trust fund established by the Highway Revenue Act of 1956; this fund has two accounts — the Highway Account and the Mass Transit Account; trust fund revenues are derived from federal highway-user taxes and fees such as motor fuel taxes; trust fund uses and expenditures are determined by law.
hinge
A point in a structure at which a member is free to rotate.
hopper
An open-top railroad car with pockets or hoppers, opening on the underside of the railcar for unloading bulk commodities.
horizontal alignment
The linear (tangent) character or specific degree of curvature describing the geometry of a defined section of highway in plain view.