When traffic is very heavy, congestion also builds at the entry to the toll plaza because of the time required for each vehicle to pay the toll. 當交通量非常大的時候，因為每車輛付通行費的時間要求，阻塞也會出現在收費區的入口處。
Make a model to help you determine the optimal number of tollbooths to deploy in a barrier-toll plaza. 建立一個模型來確定在一個容易造成阻塞的收費區中應該設置的收費亭的最優數量。
It can be in a vending or gumball machine, pay phone or toll plaza. 地點可以是自動販賣機或是糖果機，，投幣電話機或收費廣場。
