diff --git a/src/visit/traversal.rs b/src/visit/traversal.rs
index e37f359..88782fa 100644
--- a/src/visit/traversal.rs
+++ b/src/visit/traversal.rs
@@ -41,6 +41,18 @@
     pub discovered: VM,
 }
 
+impl<N, VM> Default for Dfs<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Dfs {
+            stack: Vec::new(),
+            discovered: VM::default(),
+        }
+    }
+}
+
 impl<N, VM> Dfs<N, VM>
 where
     N: Copy + PartialEq,
@@ -125,6 +137,19 @@
     pub finished: VM,
 }
 
+impl<N, VM> Default for DfsPostOrder<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        DfsPostOrder {
+            stack: Vec::new(),
+            discovered: VM::default(),
+            finished: VM::default(),
+        }
+    }
+}
+
 impl<N, VM> DfsPostOrder<N, VM>
 where
     N: Copy + PartialEq,
@@ -232,6 +257,18 @@
     pub discovered: VM,
 }
 
+impl<N, VM> Default for Bfs<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Bfs {
+            stack: VecDeque::new(),
+            discovered: VM::default(),
+        }
+    }
+}
+
 impl<N, VM> Bfs<N, VM>
 where
     N: Copy + PartialEq,
@@ -279,6 +316,18 @@
     ordered: VM,
 }
 
+impl<N, VM> Default for Topo<N, VM>
+where
+    VM: Default,
+{
+    fn default() -> Self {
+        Topo {
+            tovisit: Vec::new(),
+            ordered: VM::default(),
+        }
+    }
+}
+
 impl<N, VM> Topo<N, VM>
 where
     N: Copy + PartialEq,