Habitat is that location where a plant or animal lives. Also, habitat includes areas that are or may be occupied by a threatened or endangered species.

A halftone is an analog image, usually a photograph, composed oSf small spots of varied size, giving the illusion of a continuous tone (for example, a newspaper photograph examined under a magnifying glass).

Handicapped refers to people who have physical or mental impairments that substantially limit one or more major life activities. In the context of transportation, the term usually refers to people for whom the use of conventional transit facilities would be impossible or would create a hardship. These people are also known as transportation handicapped or as people who have a public transportation disability.

Handling Cylinders are cylinders used to determine when the concrete strength is adequate to remove nonstressed concrete members from the casting forms.

Hard coding is a method of eliminating the need for manually coding input data on source documents when the computer has permanently associated certain input data with specific accounting transactions.

A hash is a function that maps keys to integers, usually to get an even distribution on a smaller set of values.

Haul is the distance or route over which a load is transported.

hazardous atmosphere Hazardous atmosphere is an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness from one or more causes. The causes include flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL); airborne combustible dust at a concentration that meets or exceeds its LFL; atmospheric oxygen concentration below 19.5 percent or above 23.5 percent; atmospheric concentration of any substance for which a dose or a permissible exposure limit is published and, any other atmospheric condition that is immediately dangerous to life or health.

Hazardous materials are any solid, liquid, or gaseous material that, because of quantity, concentration or physical, chemical, or infectious characteristics, may (a) cause or significantly contribute to an increase in mortality or an increase in serious irreversible or incapacitating illness, or (b) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, disposed of or otherwise managed.

Hazardous waste, as defined in federal law, is a solid waste or combination of solid wastes that, because of quantity, concentration or physical, chemical or infectious characteristics, may: (a) cause or significantly contribute to an increase in mortality or an increase in serious irreversible or incapacitating illness; or (b) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, disposed of or otherwise managed.

Hazardous waste operations is an emergency response activity.

Head (static) is the height of water above any plane or point of reference. The energy possessed by each unit of weight of a liquid, expressed as the vertical height through which a unit of weight would have to fall to release the average energy possessed. The standard unit of measure shall be the foot.

The header bank is the embankment placed directly at the beginning or ending of a bridge structure.

A headwall is the supporting structures at the ends of drainage structures.

Headwater is that depth of flood water impounded upstream of a culvert due to the influence of the culvert restriction, friction, and configuration.

Heat or lot is the amount of material produced during a certain period of time determined by the producer.

Heat sink is a solid or liquid placed in the microwave oven to absorb energy after the moisture has been driven from a test specimen. The heat sink reduces the possibility of over-heating the specimen.

The height of cover is the distance from crown of a culvert or conduit to the finished road surface or the base of rail.

The hierarchy of Texas highways is: Interstate, US, SH, State Loops or Spurs, FM/RM, County Roads (CR), and Business Routes (BR).

Terms which define a condition in which a technological architecture has been constructed with redundant (or backup) systems, components and/or communication pathways such that it is highly resistant to failure.

Contained in the Traffic Operations Standard Plans.

High mast lighting is lighting fixtures mounted at heights of 100 feet or more.

A fee charged to vehicles using an HOV facility and carrying fewer than the required number of occupants.

High occupancy/toll (HOT) lanes serve both HOV users and those willing to pay a toll to use the restricted lane (typically during hours of peak demand).

A vehicle having more than one occupant. Examples include carpools, vanpools, buses, and mini-buses. Transportation systems may encourage HOV use by having designated HOV lanes and designating a minimum number of occupants required to use these lanes.

High occupancy vehicle (HOV) lanes provide preferential treatment to carpools, vanpools and buses carrying a minimum number of people in each vehicle. Dedicated lanes are restricted for this purpose, either on a part-time or full-time basis.

High pressure sodium vapor lamps are electric light sources in which light is generated by an arc discharge in an atmosphere containing sodium mercury and xenon vapors.

A high risk area is a room or location that contains information resources used to support critical department functions that, if lost, would cause a work stoppage crucial to department operations. The central mainframe computer room is a high risk area.

A rail service having the characteristics of intercity rail service which operates primarily on a dedicated guideway or track not used, for the most part, by freight, including, but not limited to, trains on welded rail, magnetically levitated (MAGLEV) vehicles on a special guideway, or other advanced technology vehicles, designed to travel at speeds in excess of those possible on other types of railroads. High Speed Rail has exclusive right of way and serves densely traveled corridors at speeds of 90 miles per hour and greater. High speed rail corridors/tracks may be shared with freight trains.

Highway is the entire width between the boundary lines of every way publicly maintained when any part thereof is open to the use of the public for purposes of vehicular travel.

A highway advisory radio refers to dedicated frequencies carrying traffic information.

The Highway Bridge Program is a federal-aid program. The program was once known as Highway Bridge Replacement and Rehabilitation Program (HBRRP).

Highway class is the rural/urban description of the lane characteristics.

The highway functional classification of routes according to use, such as arterial, collector, and local. This classification is for transportation planning and design purposes.

The highway cost index is a measure of the effect of inflation on the highway dollar. Used until 1985 to determine the amount of transfer from the General Fund.

Highway maintenance and service equipment includes both on-road and off-road equipment.

A highway-overpass is a grade separation where the subject highway passes over intersecting highway.

A highway safety plan documents top priority highway safety problems and the strategies to address them. The plan is submitted to and approved by the National Highway Traffic Safety Administration and the Federal Highway Administration for funding under the federal 402 program.

Highway structure is a general term to refer to various highway design features which are of particular concern to utility installations, i.e., bridges.

Highway system designation is the description of highways, from point "A" to point "B," including highway system (i.e., FM, IH), highway number, direction, mileage, and counties affected.

The Highway Trust Fund is a federal account established by law to hold receipts collected by the government and earmarked for highway programs and a portion of the federal mass transit program. It is supported by the federal gasoline tax and other user taxes.

A highway-underpass is a grade separation where the subject highway passes under an intersecting highway.

A highway voucher is TxDOT’s voucher number.

Historic is Native American and Euro-American archaeological sites in North America dating after A.D. 1492.

A Historic Bridge Team is an interdisciplinary team organized by the Bridge Division project manager to handle historic bridge projects.

Buildings, structures, objects, sites or districts with historical or archeological significance that are listed in, or eligible for listing in, the National Register of Historic Places.

A historic sign is a sign that is attached to and is a contributing feature of a historic building or structure.

Home-based work trips are trips between a person’s home and place of employment for the purpose of working.

Home-based non-work trips are trips between a person’s home and other destinations which are not for the purpose of working.

Host-based is information, such as audit data from a single host, which may be used to detect intrusions.

Horizontal alignment is the positioning of a roadway, as shown in the plan view, using a series of straight lines called tangents connected by circular curves.

A horizontal curve is a simple, circular arc joining two straight lines known as tangents.

The horizontal (eye) gaze nystagmus is an involuntary jerking of the eyes that occurs as a person moves his or her eyes to the side when under the influence of alcohol or certain other drugs. HGN is one of the indicators used in the Standardized Field Sobriety Test.

Horizontal entrance angle is the angle, in a plane parallel to the base of the tile, between a line in the direction of the incident light and a line perpendicular to the leading edge of the reflective surface.

Hot bins are aggregate bins that feed directly into the weight-box or the proportioning mechanism.

Hot mix applies to a paving mixture of asphalt cement and aggregate which have been combined while hot. It is also placed and compacted above 175º F. Temperature is a critical factor in the workability of the mix, as well as the durability of the finished pavement.

Hot soak emissions are evaporated gasoline emissions occurring after the end of a vehicle trip due to the heating of the fuel, fuel lines and fuel vapors.

A household is an occupied dwelling unit in which occupants form a single economic unit regarding housing.

The household size is the number of persons living in one household. In travel demand modeling household size is generally referred to as 1, 2, 3, 4, or 5or more person households.

The Houston automatic spooling program is a control system for submitting jobs to a large scale computer that allows the operators to control the flow of jobs through the system.

The Houston District is a TxDOT district office including the following counties: Brazoria, Fort Bend, Galveston, Harris, Montgomery, and Waller. Area offices are located in Brazoria; Fort Bend; Galveston; East, northeast, northwest, and south Harris County, Montgomery and Waller. The Houston district also operates the Galveston/Port Bolivar ferries and houses a Vehicle Titles and Registration Regional Office.

A hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind.

A Historically Underutilized Business (HUB) Subcontracting Plan is a requirement placed on vendors to encourage their utilization of historically underutilized businesses where subcontracting is practical. Applies to all delegated purchases with an estimated total cost of $100,000 or more where there are subcontracting opportunities for the procurement. [TGC §2161.181-182, 1 TAC §111.11]

Human environment means interpreted comprehensively to include the natural and physical environment and the relationship of people with that environment.

The Human Resources Division manages employee services, oversees employee performance planning and evaluation, and administers the department’s recruitment and training program.

Human Resources Management is one of TxDOT’s seven functional areas. The goal of the Human Resources Management is to provide comprehensive human resources services to all TxDOT employees, prospective employees and other users.

Hydraulics is a branch of engineering dealing with liquids in motion.

Hydric soils are wetland soils. These soils favor the production and regeneration of hydrophytic vegetation. A hydric soil is either saturated with water and virtually free of oxygen at or near the surface during significant periods of the growing season or the soil is flooded for significant periods when the soil temperature is above 5 degrees centigrade. Field indicators may include gray color or mottling with chrome, manganese or iron concentrations, an organic horizon, free water within the root zone and a sulfur odor in the soil.

Hydrogen ion refers to acidity or alkalinity of water or soil. An ion is a charged atom or group of atoms in solution or in a gas. Solutions contain equivalent numbers of positive and negative ions.

Hydrology is the study of the occurrence and distribution of the natural waters of the earth.

Hydrophytic vegetation refers to wetland plant species. Plants adapted for life within habitats that have permanent or alternating dry and inundated and/or saturated soil conditions.

Hydroseeding is a method of broadcasting seed and sometimes lime, fertilizer, and mulch together in a mixture of water.

Hyperlinks are informational pathways that users of an online document can select to summon new topics, or more detailed information by clicking a mouse. Hyperlinks can unite different topics and show their relationships through the retrieval of information from an existing Web site or page, a specific file, or document.

Hypertext is usually a word or term that is linked to a definition, file or document.

Hypertext Markup Language is the language used to publish documents on the Word Wide Web portion of the Internet.

Hypertext Transport Protocol is an information-serving protocol used to transfer files on the World Wide Web. Graphics, text and sounds can be transmitted.