diff --git a/ortools/constraint_solver/samples/VrpPickupDelivery.cs b/ortools/constraint_solver/samples/VrpPickupDelivery.cs
index 4cc2da78d1..8999054fa6 100644
--- a/ortools/constraint_solver/samples/VrpPickupDelivery.cs
+++ b/ortools/constraint_solver/samples/VrpPickupDelivery.cs
@@ -118,18 +118,19 @@ public class VrpPickupDelivery {
 
     // Define cost of each arc.
     // [START arc_cost]
-    int transitCostIndex = routing.RegisterTransitCallback(
+    int transitCallbackIndex = routing.RegisterTransitCallback(
       (long fromIndex, long toIndex) => {
+        // Convert from routing variable Index to distance matrix NodeIndex.
         var fromNode = manager.IndexToNode(fromIndex);
         var toNode = manager.IndexToNode(toIndex);
         return data.GetDistanceMatrix()[fromNode, toNode]; }
     );
-    routing.SetArcCostEvaluatorOfAllVehicles(transitCostIndex);
+    routing.SetArcCostEvaluatorOfAllVehicles(transitCallbackIndex);
     // [END arc_cost]
 
     // Add Distance constraint.
     // [START distance_constraint]
-    routing.AddDimension(transitCostIndex, 0, 3000,
+    routing.AddDimension(transitCallbackIndex, 0, 3000,
                          true,  // start cumul to zero
                          "Distance");
     RoutingDimension distanceDimension = routing.GetMutableDimension("Distance");
diff --git a/ortools/constraint_solver/samples/VrpPickupDelivery.java b/ortools/constraint_solver/samples/VrpPickupDelivery.java
index 29574c691d..60cd2736af 100644
--- a/ortools/constraint_solver/samples/VrpPickupDelivery.java
+++ b/ortools/constraint_solver/samples/VrpPickupDelivery.java
@@ -82,18 +82,18 @@ public class VrpPickupDelivery {
   /// two different indices.
   static class ManhattanDistance extends LongLongToLong {
     public ManhattanDistance(DataModel data, RoutingIndexManager manager) {
-      // precompute distance between location to have distance callback in O(1)
-      distanceMatrix_ = data.distanceMatrix;
-      indexManager_ = manager;
+      distanceMatrix = data.distanceMatrix;
+      indexManager = manager;
     }
     @Override
     public long run(long fromIndex, long toIndex) {
-      int fromNode = indexManager_.indexToNode(fromIndex);
-      int toNode = indexManager_.indexToNode(toIndex);
-      return distanceMatrix_[fromNode][toNode];
+      // Convert from routing variable Index to distance matrix NodeIndex.
+      int fromNode = indexManager.indexToNode(fromIndex);
+      int toNode = indexManager.indexToNode(toIndex);
+      return distanceMatrix[fromNode][toNode];
     }
-    private final long[][] distanceMatrix_;
-    private final RoutingIndexManager indexManager_;
+    private final long[][] distanceMatrix;
+    private final RoutingIndexManager indexManager;
   }
   // [END manhattan_distance]
 
@@ -144,13 +144,13 @@ public class VrpPickupDelivery {
     // Define cost of each arc.
     // [START arc_cost]
     LongLongToLong distanceEvaluator = new ManhattanDistance(data, manager);
-    int transitCostIndex = routing.registerTransitCallback(distanceEvaluator);
-    routing.setArcCostEvaluatorOfAllVehicles(transitCostIndex);
+    int transitCallbackIndex = routing.registerTransitCallback(distanceEvaluator);
+    routing.setArcCostEvaluatorOfAllVehicles(transitCallbackIndex);
     // [END arc_cost]
 
     // Add Distance constraint.
     // [START distance_constraint]
-    routing.addDimension(transitCostIndex, 0, 3000,
+    routing.addDimension(transitCallbackIndex, 0, 3000,
         true, // start cumul to zero
         "Distance");
     RoutingDimension distanceDimension = routing.getMutableDimension("Distance");
diff --git a/ortools/constraint_solver/samples/vrp_pickup_delivery.cc b/ortools/constraint_solver/samples/vrp_pickup_delivery.cc
index 224ef1fa6d..ff94ab6ed0 100644
--- a/ortools/constraint_solver/samples/vrp_pickup_delivery.cc
+++ b/ortools/constraint_solver/samples/vrp_pickup_delivery.cc
@@ -140,17 +140,19 @@ void VrpGlobalSpan() {
 
   // Define cost of each arc.
   // [START arc_cost]
-  const int transit_cost_id = routing.RegisterTransitCallback(
+  const int transit_callback_index = routing.RegisterTransitCallback(
       [&data, &manager](int64 from_index, int64 to_index) -> int64 {
-        return data.distance_matrix[manager.IndexToNode(from_index).value()]
-                                   [manager.IndexToNode(to_index).value()];
+        // Convert from routing variable Index to distance matrix NodeIndex.
+        auto from_node = manager.IndexToNode(from_index).value();
+        auto to_node = manager.IndexToNode(to_index).value();
+        return data.distance_matrix[from_node][to_node];
       });
-  routing.SetArcCostEvaluatorOfAllVehicles(transit_cost_id);
+  routing.SetArcCostEvaluatorOfAllVehicles(transit_callback_index);
   // [END arc_cost]
 
   // Add Distance constraint.
   // [START distance_constraint]
-  routing.AddDimension(transit_cost_id,  // transit callback
+  routing.AddDimension(transit_callback_index,  // transit callback
                        0,                // no slack
                        3000,             // vehicle maximum travel distance
                        true,             // start cumul to zero
diff --git a/ortools/constraint_solver/samples/vrp_pickup_delivery.py b/ortools/constraint_solver/samples/vrp_pickup_delivery.py
index 07092bbe7f..d1854ce5e0 100755
--- a/ortools/constraint_solver/samples/vrp_pickup_delivery.py
+++ b/ortools/constraint_solver/samples/vrp_pickup_delivery.py
@@ -120,12 +120,12 @@ def print_solution(data, manager, routing, assignment):
         plan_output = 'Route for vehicle {}:\n'.format(vehicle_id)
         route_distance = 0
         while not routing.IsEnd(index):
-            plan_output += ' {} ->'.format(manager.IndexToNode(index))
+            plan_output += ' {} -> '.format(manager.IndexToNode(index))
             previous_index = index
             index = assignment.Value(routing.NextVar(index))
             route_distance += routing.GetArcCostForVehicle(
                 previous_index, index, vehicle_id)
-        plan_output += ' {}\n'.format(manager.IndexToNode(index))
+        plan_output += '{}\n'.format(manager.IndexToNode(index))
         plan_output += 'Distance of the route: {}m\n'.format(route_distance)
         print(plan_output)
         total_distance += route_distance
@@ -143,9 +143,7 @@ def main():
     # Create the routing index manager.
     # [START index_manager]
     manager = pywrapcp.RoutingIndexManager(
-        len(data['distance_matrix']),
-        data['num_vehicles'],
-        data['depot'])
+        len(data['distance_matrix']), data['num_vehicles'], data['depot'])
     # [END index_manager]
 
     # Create Routing Model.
@@ -158,19 +156,20 @@ def main():
     # [START arc_cost]
     def distance_callback(from_index, to_index):
         """Returns the manhattan distance between the two nodes."""
+        # Convert from routing variable Index to distance matrix NodeIndex.
         from_node = manager.IndexToNode(from_index)
         to_node = manager.IndexToNode(to_index)
         return data['distance_matrix'][from_node][to_node]
 
-    transit_cost_id = routing.RegisterTransitCallback(distance_callback)
-    routing.SetArcCostEvaluatorOfAllVehicles(transit_cost_id)
+    transit_callback_index = routing.RegisterTransitCallback(distance_callback)
+    routing.SetArcCostEvaluatorOfAllVehicles(transit_callback_index)
     # [END arc_cost]
 
     # Add Distance constraint.
     # [START distance_constraint]
     dimension_name = 'Distance'
     routing.AddDimension(
-        transit_cost_id,
+        transit_callback_index,
         0,  # no slack
         3000,  # vehicle maximum travel distance
         True,  # start cumul to zero
@@ -214,4 +213,4 @@ def main():
 
 if __name__ == '__main__':
     main()
-    # [END program]
+# [END program]