We　restudy　the　master-equation　approach　applied　to　aggregation　in　a　one-dimensional　freeway,　where　the　decay　transition　probabilities　for　the　jump　processes　are　reconstructed　based　on　a　car-following　model.　According　to　the　reconstructed　transition　probabilities,　the　clustering　behaviours　and　the　stochastic　properties　of　the　master　equation　in　a　one-lane　freeway　traffic　model　are　investigated　in　detail.　The　numerical　results　show　that　the　size　of　the　clusters　initially　below　the　critical　size　of　the　unstable　cluster　and　initially　above　that　of　the　unstable　cluster　all　enter　the　same　stable　state,　which　also　accords　with　the　nucleation　theory　and　is　known　from　the　result　in　earlier　work.　Moreover,　we　have　obtained　more　reasonable　parameters　of　the　master　equation　based　on　some　results　of　cellular　automata　models.