[b]Density——[/b]thenumberofvehiclesoccupyingaroadlaneperunitlengthatagiveninstant
[b]Flow——[/b]thenumberofvehiclespassingapointperunitoftime;oftencalledvolumewhenthetimeunitisonehour
[b]Gap——[/b]thetimeintervalbetweenthepassageofconsecutivevehiclesmovinginthesamestream,measuredbetweentherearoftheleadvehicleandthefrontofthefollowingvehicle
[b]Headway——[/b]thetimeintervalbetweenpassageofconsecutivevehiclesmovinginthesamestream,measuredbetweencorrespondingpoints(e
frontbumper)onsuccessivevehicles
[b]InterruptedFlow——[/b]occurswhenflowisperiodicallyinterruptedbyexternalfixtures,primarilytrafficcontroldevices
[b]JamDensity——[/b]thedensitywhenspeedandflowarezero
[b]PHF(PeakHourFactor)——[/b]Thisdescribestherelationshipbetweenhourlyvolumeandthemaximumrateofflowwithinthehour:PHF=hourlyvolume/maxi