### structure | barrier | rail:

Light rail
* is able to run in tunnels, along hills, elevated tracks and at street level.
* is an awkward way to move people
  - efficient and cost-effective form of mass transit
  - electrically powered transit system
  - built mainly on ground-level
  - characterized by short headways, frequent stops, and service within an urban area
  - only a trolley system, and trolleys died out a half a century ago
  - significantly more expensive per mile than monorail
  - touted as a means of reducing urban traffic congestion
* means business.
* medium-capacity train that is powered by electric motors fed by overhead wires.
* modern version of old-time street cars.
* operates on special tracks on or along streets and is powered by overhead electric power.
* wastes energy.

Regional rail
* helps conserve energy.
* improves opportunities for access to jobs.

Railing
* are barriers.
* are located in decks
  - houses
  - parks
  - porchs
  - railway stations
  - ships
  - stairwells
  - materials
* are used for guidance
  - protection
* includes bases
  - sections

Reproductive barrier
* Most reproductive barriers lead to speciation.
* prevent interbreeding between closely related species.

Root barrier
* Most root barriers are made of metal.
* are great tools to prevent tree-root colonization and damage
* block tree roots from colonizing soil in and around structures.

Seawall
* also eliminate and obstruct natural bluff erosion and beach nourishment.
* are piles of rock and debris that are piled in front of the cliff.
* have a different but equally destructive effect
  - the biggest impact on everyone else
* now sit where once there was beach.
* protect buildings but destroy beaches.

### structure | barrier:

Ticket barrier
+ Amersham station: Metropolitan Line stations :: Buckinghamshire :: 1892 establishments
  * Ticket barriers are in operation.
+ Charing Cross railway station: Railway stations in London
  * The station takes its name from the central London road junction of Charing Cross. The front of the rail station faces The Strand. The other end is the northern end of Hungerford Bridge, which is crossed by all trains serving the station. Ticket barriers control access to all platforms, although the bridge entrance has no barriers.

Vapor barrier
* are important in controlling moisture in insulation.
* control the flow of moisture through the building envelope
  - moisture from entering or exiting an interior wall
* help prevent moisture from getting into the insulation.
* keep moisture from penetrating and condensing in the insulation.
* prevent moisture vapor from moving from one area to another.
* slow the movement of water vapor through building materials.

### structure:

Barrow
* achieve their maximum lean growth rate at lighter weights than gilts.
* are burial mounds
  - male pigs who have been castrated
* eat more feed and grow faster than gilts.
* generally have similar lean growth rates, but higher feed intakes than gilts.
* grow faster, eat more and have higher nutrient requirements than gilts.
* have both higher daily growth rates and feed intakes than gilts
  - higher rates of mortality due to ulcers
  - more energy available for fat deposition from their higher feed intakes