diff --git a/src/entities/entities.ts b/src/entities/entities.ts
index 4f1f1dc..1feef84 100644
--- a/src/entities/entities.ts
+++ b/src/entities/entities.ts
@@ -1,9 +1,12 @@
-export interface IEntityWithIdAndOptionalTimestamp {
-  id: string;
+export interface IEntityWithOptionalTimestamp {
   millisecondsSinceEpoch?: number;
 }
 
-export interface ISystem extends IEntityWithIdAndOptionalTimestamp {
+export interface IEntityWithId {
+  id: string;
+}
+
+export interface ISystem extends IEntityWithId, IEntityWithOptionalTimestamp {
   name: string;
 }
 
@@ -12,33 +15,33 @@ export interface ICoordinates {
   longitude: number;
 }
 
-export interface IRoute extends IEntityWithIdAndOptionalTimestamp {
+export interface IRoute extends IEntityWithId, IEntityWithOptionalTimestamp {
   name: string;
   color: string;
   polylineCoordinates: ICoordinates[];
   systemId: string;
 }
 
-export interface IStop extends IEntityWithIdAndOptionalTimestamp {
+export interface IStop extends IEntityWithId, IEntityWithOptionalTimestamp {
   name: string;
   systemId: string;
   coordinates: ICoordinates;
 }
 
-export interface IShuttle extends IEntityWithIdAndOptionalTimestamp {
+export interface IShuttle extends IEntityWithId, IEntityWithOptionalTimestamp {
   coordinates: ICoordinates;
   name: string;
   routeId: string;
   systemId: string;
 }
 
-export interface IEta {
+export interface IEta extends IEntityWithOptionalTimestamp {
   secondsRemaining: number;
   shuttleId: string;
   stopId: string;
 }
 
-export interface IOrderedStop {
+export interface IOrderedStop extends IEntityWithId, IEntityWithOptionalTimestamp {
   nextStop?: IOrderedStop;
   previousStop?: IOrderedStop;
   routeId: string;