The　allocation　mechanism　of　carbon　abatement　quotas　is　a　vital　issue　in　the　carbon　emission　abatement　(CEA)　for　the　environment　and　sustainability.　The　conventional　CEA　allocation　focuses　on　the　imposition　of　carbon　quotas　but　hardly　considers　the　techniques　or　mechanisms　of　abatement.　The　neglect　of　the　abatement　mechanisms　may　cause　inapplicability　and　unavailability　in　the　practical　implementation　of　CEA　allocation.　To　fill　this　gap,　this　paper　firstly　recognizes　and　distinguishes　two　kinds　of　non-separable　relationships　among　energy　inputs,　capital　investments,　and　carbon　emission.　Thereafter,　three　carbon　abatement　mechanisms　are　formed　and　defined.　Then,　three　scenarios　of　carbon　abatement,　named　managerial,　technical,　and　hybrid　scenarios,　are　constructed　based　on　the　carbon　abatement　mechanism,　in　which　the　carbon　emission　is,　respectively,　abated　by　reducing　energy　inputs　and　increasing　capital　investment　and　the　hybrid　measure　of　energy　decrease　and　capital　investment　increase.　With　the　developed　carbon　abatement　mechanisms,　a　carbon　abatement　allocation　application　of　the　regional　highway　transportation　systems　in　China　is　illustrated.　It　finds　that　the　carbon　abatement　allocations　based　on　the　proposed　carbon　abatement　mechanisms　help　to　narrow　the　regional　highway　transportation　system　gaps　in　China,　and　the　outputs　perform　the　best　under　the　managerial　scenario.　The　Eastern　bears　more　carbon　abatement　burdens　than　the　Central　and　West　under　both　managerial　and　technical　scenarios.　The　Central　and　West　can　improve　their　outputs　and　bear　more　carbon　abatement　burden　under　hybrid　scenarios.　The　central　authority　can　choose　the　CEA　technique　and　allocation　scheme　in　line　with　its　preference　and　observation.