         return model
     }
     
-    private static func factoryMinutes(
-        duration:TimeInterval) -> DPlanTravelDuration
+    private static func factoryMinutes(duration:TimeInterval) -> DPlanTravelDuration
     {
-        let minutes:TimeInterval = duration / kSecondsInMinute
+        let minutes:TimeInterval = duration / DPlanTravelDuration.Constants.secondsInMinute
+        
         let model:DPlanTravelDuration = DPlanTravelDuration(
             type:DPlanTravelDurationType.minutes,
             amount:minutes)

        return model
    }
    
    private static func factorySeconds(
        duration:TimeInterval) -> DPlanTravelDuration
    {
        let model:DPlanTravelDuration = DPlanTravelDuration(
            type:DPlanTravelDurationType.seconds,


extension DPlanTravelDuration
{
    //MARK: private
    
    private static func factoryTotalDuration(travels:[DPlanTravel]) -> TimeInterval
    {
        var duration:TimeInterval = 0
        
