A road network is modeled as a directed graph. Nodes $A$, $B$, $C$, $D$, and $E$ represent intersections, and the edges represent roads with maximum capacities (in vehicles per hour): $AB = 800$, $AC = 600$, $BC = 200$, $BD = 500$, $CD = 300$, $CE = 700$, and $DE = 400$. Flow conservation holds at intermediate nodes $B, C, D$. What is the maximum traffic flow (in vehicles per hour) that can travel from source node $A$ to sink node $E$?