You need to upgrade your Flash Player
Download the most recent Flash plugin here.


machine control grading
Also called machine guidance.
main beam
A beam supporting the bridge spans and bearing directly onto a column or wall.
main line
Primary rail line over which trains operate between terminals; it excludes sidings, and yard and industry tracks.
main track
A railroad's primary track that usually extends great distances, it usually carries both freight and passenger trains.
The maintenance of railroad rights of way, it can include procedures from the initial grading of the right of way to its general upkeep and eventual dismantling.
major air carrier
An airline with annual revenue of more than $1 billion.
Manual on Uniform Traffic Control Devices (MUTCD)
This manual is published by the Federal Highway Administration and used by most departments of transportation across the country as the standard for traffic control devices. These devices include signals, signs and pavement striping.
Moving Ahead for Progress in the 21st Century (MAP-21)
Passed on June 29, 2012; signed on July 6, 2012 (Pub. L. 112-141)
marked pedestrian crossing
Any portion of a roadway at an intersection or elsewhere that is distinctly indicated for pedestrian crossing by lines or other markings on the surface of the roadway.
Mass Transit Account
The federal account, established by the Surface Transportation Assistance Act of 1982, into which a designated portion of the federal Highway Trust Fund revenue from motor fuel taxes is placed (1.5 cents in 1994); this account is used for federal mass transportation assistance.
mass transportation
Transportation by bus, rail, boat or other conveyance, either publicly or privately owned, that provides general or special service to the public on a regular and continuing basis (not including school bus, charter or sight-seeing service).
measures of effectiveness (MOEs)
Descriptions of driver or traffic behaviors that quantify the level of safety or service provided by facility or treatment to drivers, passengers or pedestrians; examples include vehicle speed, trajectory, delay and similar measures; MOEs are the dependent measures (e.g., the effects/behaviors resulting from introduction of a treatment or countermeasure).
An island in the center of a street or intersection to protect pedestrians and provide landscaping; medians prevent passing and left turns, separate opposing travel lanes, and provide visual enhancement.
median barriers
A longitudinal system of physical barriers used to prevent an errant vehicle from crossing the portion of the divided highway separating traffic moving in opposite directions.
An individual angle, beam, plate or built piece intended to become an integral part of an assembled frame or structure.
merge steering control (MSC) zone
Used with interchange/ramp entry traffic models, it is the zone in which the driver enters the freeway and positions the vehicle in the nearest lane on the mainline.
metropolitan planning organization (MPO)
The organization designated by local elected officials to be responsible for carrying out the region transportation planning process and other regional planning processes; the MPO must be in place in every urbanized area with a population greater than 50,000; the MPO's responsibilities include the 20-year long-range plan and transportation improvement program.
Metropolitan Transportation Improvement Program (MTIP)
A staged, multiyear, intermodal program of transportation projects that is consistent with the metropolitan transportation plan.
A thin surface treatment (about inch thick) used as a preventive maintenance tool to extend pavement life. It provides a new roadway wearing surface that helps to slow pavement deterioration caused by water and the environment. It also can correct minor surface profile irregularities.
A green paddle-shaped sign alongside roads and highways that indicates 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.
minimum required visibility distance (MRVD)
The distance necessary to permit detection and comprehension, plus driver decision making, response selection and completion of vehicle maneuver, if necessary.
minority business enterprise (MBE)
A business owned and operated by one or more individuals who are defined as minorities under U.S. Department of Transportation regulations; see also "disadvantaged business enterprise."
mitigation measures
Specific design commitments made during the environmental evaluation and study process that serve to moderate or lessen impacts deriving from the proposed action; these measures may include planning and development commitments, environmental measures, right-of-way improvements, and agreements with resource or other agencies to effect construction or post construction action.
The ability to move people and goods from place to place, or the potential for movement, mobility improves when the transportation network is refined or expanded to improve capacity of one or more modes, thus, allowing people and goods to move more quickly toward a particular destination.
A general term to describe a manner of transportation; walking, driving, taking a bus or train or bicycling are all modes of transportation.
multilevel car
A long railroad flatcar designed with one or more deck levels in addition to the car's main deck; used to haul new automobiles and trucks.
Concerning or involving more than one transportation mode.