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The product of centerline-miles and number of lanes. Example: A four-lane road, 2 miles long, has eight lane-miles.
Legibility Index (LI)
Used to describe the relative legibility of different letter styles; it is calculated from the distance at which a character, word or message is legible divided by the size of the letters on the sign.
less-than-truckload (LTL)
The quantity of freight that is less than that is required for application of a trailer load rate.
The process by which the Iowa DOT requests and decides on bids from competing companies for work on transportation projects.
level of service
A description of the quality of service that can be expected by users of transportation facilities.
level of service (LOS)
A qualitative measure describing operational conditions within a traffic stream, based upon service measures, such as speed and travel time, freedom to maneuver, traffic interruptions, comfort and convenience; LOS A represents completely free flow of traffic allowing traffic to maneuver unimpeded; LOS F represents a complete breakdown in traffic flow resulting in stop and go travel; LOS is typically calculated based upon peak-hour conditions.
light rail transit
A type of electric rail system with a "light" total passenger carrying capacity compared to the capacity of heavy rail transit.
limited access highway
Highway designated for through traffic with very few entrances and exits.
limited sight distance
A restricted preview of the traveled way downstream due to a crest vertical curvature or horizontal curvature of the roadway, or to blockage or obstruction by a natural or constructed roadway feature or by (an)other vehicle(s).
line capacity
The maximum number of trains that can operate safely and reliably over a given segment of track during a given period of time.
line-haul service
The movement over the tracks of a carrier from one city to another, not including the switching service.
liquefied natural gas (LNG)
An alternative fuel; a natural gas cooled to below its boiling point of -260 degrees Fahrenheit so that it becomes a liquid; stored in a vacuum bottle-type container at very low temperatures and under moderate pressure; LNG vapor is lighter than air.
longer combination vehicles (LCV)
Commercial motor vehicles with two or more trailers.
lower chord
The bottom horizontal member of a truss.
A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and to connect the lamps to the power supply.
The luminous intensity or brightness of any surface in a given direction, per unit of projected area of the surface as viewed from that direction, independent of viewing distance; the International System of Units is the candela per square meter.
luminance contrast
The difference between the luminance of a target area and a surrounding background area, divided by the background luminance alone (e.g., lane marking minus lane pavement surface, divided by pavement surface).