Guide rail in the context of "Rubber-tyred tram"

A gun is a device that propels a projectile using pressure or explosive force. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns or cannons), or gas (e.g. light-gas gun). Solid projectiles may be free-flying (as with bullets and artillery shells) or tethered (as with Tasers, spearguns and harpoon guns). A large-caliber gun is also called a cannon. Guns were designed as weapons for military use, and then found use in hunting. Now, there are guns, e.g., toy guns, water guns, paintball guns, etc., for many purposes.

The means of projectile propulsion vary according to designs, but are traditionally effected pneumatically by a high gas pressure contained within a barrel tube (gun barrel), produced either through the rapid exothermic combustion of propellants (as with firearms), or by mechanical compression (as with air guns). The high-pressure gas is introduced behind the projectile, pushing and accelerating it down the length of the tube, imparting sufficient launch velocity to sustain its further travel towards the target once the propelling gas ceases acting upon it after it exits the muzzle. Alternatively, new-concept linear motor weapons may employ an electromagnetic field to achieve acceleration, in which case the barrel may be substituted by guide rails (as in railguns) or wrapped with magnetic coils (as in coilguns).

A rubber-tyred metro or rubber-tired metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tires that run on a roll way inside guide bars for traction. Traditional, flanged steel wheels running on rail tracks provide guidance through switches and act as backup if tyres fail. Most rubber-tyred trains are purpose-built and designed for the system on which they operate. Guided buses are sometimes referred to as 'trams on tyres', and compared to rubber-tyred metros.

The rail profile is the cross-sectional shape of a rail as installed on a railway or railroad, perpendicular to its length.

Early rails were made of wood, cast iron or wrought iron. All modern rails are hot rolled steel with a cross section (profile) approximate to an I-beam, but asymmetric about a horizontal axis (however see grooved rail below). The head is profiled to resist wear and to give a good ride, and the foot profiled to suit the fixing system.

A roll way or running pad is the pad placed on a concrete slab or on the ties on the outside of the 1,435 mm (4 ft 8+1⁄2 in) conventional track along both running rails of a rubber-tyred metro or along the unconventional track of a tram. The rubber-tyred wheels roll directly on the roll ways.

• With a conventional track:
  • The ones of the Montreal Metro are precast concrete on a concrete slab.
  • The ones of the Paris Métro are H-steel on ties.
  • The ones of the Mexico City Metro are H-steel.
  • The ones of the Santiago Metro are precast concrete below ground and H-steel above ground.
  • The ones of the Lausanne Métro Line M2 are H-steel.
  • The ones of the Lyon Metro (lines A, B and D) are H-steel.
• Without a conventional track:
  • The ones of the Lille Metro are precast concrete.
  • The ones of the Toulouse Metro are precast concrete.
  • The ones of the Sapporo Municipal Subway are flat steel with a central guide rail.
  • Busan Subway Line 4 runs directly on a concrete slab between guide bars.
  • Many people mover systems, such as Crystal Mover, run directly on concrete slabs or other surfaces between guide bars.
  • Some guided buses, rubber-tyred trams, such as Translohr and Bombardier Guided Light Transit, use concrete slabs while being guided by a single central rail.