diff --git a/src/repositories/shuttle/RedisShuttleRepository.ts b/src/repositories/shuttle/RedisShuttleRepository.ts
index a18ca58..930b336 100644
--- a/src/repositories/shuttle/RedisShuttleRepository.ts
+++ b/src/repositories/shuttle/RedisShuttleRepository.ts
@@ -117,7 +117,7 @@ export class RedisShuttleRepository extends EventEmitter implements ShuttleGette
   private createEtaKey = (shuttleId: string, stopId: string) => `shuttle:eta:${shuttleId}:${stopId}`;
   private createOrderedStopKey = (routeId: string, stopId: string) => `shuttle:orderedstop:${routeId}:${stopId}`;
   private createShuttleLastStopKey = (shuttleId: string) => `shuttle:laststop:${shuttleId}`;
-  private createHistoricalEtaTimeSeriesKey =(routeId: string, fromStopId: string, toStopId: string) => {
+  private createHistoricalEtaTimeSeriesKey = (routeId: string, fromStopId: string, toStopId: string) => {
     return `shuttle:eta:historical:${routeId}:${fromStopId}:${toStopId}`;
   }
 
@@ -446,7 +446,7 @@ export class RedisShuttleRepository extends EventEmitter implements ShuttleGette
     const lastOrderedStop = await this.getOrderedStopByRouteAndStopId(shuttle.routeId, lastStopArrival.stopId);
     const nextStop = lastOrderedStop?.nextStop;
     if (nextStop == null) return;
-    
+
     const travelTimeSeconds = await this.getAverageTravelTimeSeconds({
       routeId: shuttle.routeId,
       fromStopId: lastStopArrival.stopId,
@@ -500,7 +500,7 @@ export class RedisShuttleRepository extends EventEmitter implements ShuttleGette
     const timeSeriesKey = this.createHistoricalEtaTimeSeriesKey(routeId, fromStopId, toStopId);
     const fromTimestamp = from.getTime();
     const toTimestamp = to.getTime();
-    const intervalMs = toTimestamp - fromTimestamp;
+    const intervalMs = toTimestamp - fromTimestamp + 1;
 
     try {
       const aggregationResult = await this.redisClient.sendCommand([
@@ -518,14 +518,14 @@ export class RedisShuttleRepository extends EventEmitter implements ShuttleGette
         return parseFloat(averageValue);
       }
 
-      throw new Error(`No historical data found for route ${routeId} from stop ${fromStopId} to stop ${toStopId}`);
+      return;
     } catch (error) {
       console.warn(`Failed to get average travel time: ${error instanceof Error ? error.message : String(error)}`);
       return;
     }
   }
 
-  private async addTravelTimeDataPoint(
+  public async addTravelTimeDataPoint(
     { routeId, fromStopId, toStopId }: ShuttleTravelTimeDataIdentifier,
     travelTimeSeconds: number,
     timestamp = Date.now(),
@@ -634,7 +634,7 @@ export class RedisShuttleRepository extends EventEmitter implements ShuttleGette
     });
   }
 
-   public async addOrUpdateStop(stop: IStop): Promise<void> {
+  public async addOrUpdateStop(stop: IStop): Promise<void> {
     const key = this.createStopKey(stop.id);
     await this.redisClient.hSet(key, this.createRedisHashFromStop(stop));
   }
diff --git a/src/repositories/shuttle/__tests__/RedisShuttleRepository.test.ts b/src/repositories/shuttle/__tests__/RedisShuttleRepository.test.ts
index 9cb2220..11314e2 100644
--- a/src/repositories/shuttle/__tests__/RedisShuttleRepository.test.ts
+++ b/src/repositories/shuttle/__tests__/RedisShuttleRepository.test.ts
@@ -253,4 +253,113 @@ describe("RedisShuttleRepository", () => {
       expect(result?.timestamp.getTime()).toBe(secondArrival.timestamp.getTime());
     });
   });
+
+  describe("getAverageTravelTimeSeconds", () => {
+    it("returns the average travel time when historical data exists", async () => {
+      const { route, stop2, stop1 } = await setupRouteAndOrderedStops();
+
+      // Add a single data point: 15 minutes travel time
+      const timestamp = new Date(2025, 0, 1, 12, 15, 0);
+      await repository.addTravelTimeDataPoint(
+        {
+          routeId: route.id,
+          fromStopId: stop1.id,
+          toStopId: stop2.id,
+        },
+        15 * 60, // 15 minutes in seconds
+        timestamp.getTime()
+      );
+
+      const travelTime = await repository.getAverageTravelTimeSeconds({
+        routeId: route.id,
+        fromStopId: stop1.id,
+        toStopId: stop2.id,
+      }, {
+        from: new Date(2025, 0, 1, 11, 0, 0),
+        to: new Date(2025, 0, 1, 13, 0, 0),
+      });
+
+      expect(travelTime).toEqual(15 * 60);
+    });
+
+    it("returns average of multiple data points", async () => {
+      const { route, stop2, stop1 } = await setupRouteAndOrderedStops();
+
+      // First trip: 10 minutes travel time
+      await repository.addTravelTimeDataPoint(
+        {
+          routeId: route.id,
+          fromStopId: stop1.id,
+          toStopId: stop2.id,
+        },
+        10 * 60, // 10 minutes
+        new Date(2025, 0, 1, 12, 0, 0).getTime()
+      );
+
+      // Second trip: 20 minutes travel time
+      await repository.addTravelTimeDataPoint(
+        {
+          routeId: route.id,
+          fromStopId: stop1.id,
+          toStopId: stop2.id,
+        },
+        20 * 60, // 20 minutes
+        new Date(2025, 0, 1, 13, 0, 0).getTime()
+      );
+
+      const averageTravelTime = await repository.getAverageTravelTimeSeconds({
+        routeId: route.id,
+        fromStopId: stop1.id,
+        toStopId: stop2.id,
+      }, {
+        from: new Date(2025, 0, 1, 11, 0, 0),
+        to: new Date(2025, 0, 1, 14, 0, 0),
+      });
+
+      // Average of 10 minutes and 20 minutes = 15 minutes = 900 seconds
+      expect(averageTravelTime).toEqual(15 * 60);
+    });
+
+    it("returns undefined when no data exists", async () => {
+      const { route, stop1, stop2 } = await setupRouteAndOrderedStops();
+
+      // Don't add any data points, just query for data that doesn't exist
+      const averageTravelTime = await repository.getAverageTravelTimeSeconds({
+        routeId: route.id,
+        fromStopId: stop1.id,
+        toStopId: stop2.id,
+      }, {
+        from: new Date(2025, 0, 1, 11, 0, 0),
+        to: new Date(2025, 0, 1, 14, 0, 0),
+      });
+
+      expect(averageTravelTime).toBeUndefined();
+    });
+
+    it("returns undefined when querying outside the time range of data", async () => {
+      const { route, stop2, stop1 } = await setupRouteAndOrderedStops();
+
+      // Add data on Jan 1
+      await repository.addTravelTimeDataPoint(
+        {
+          routeId: route.id,
+          fromStopId: stop1.id,
+          toStopId: stop2.id,
+        },
+        15 * 60, // 15 minutes
+        new Date(2025, 0, 1, 12, 15, 0).getTime()
+      );
+
+      // Query for Jan 2 (no data should exist in this range)
+      const averageTravelTime = await repository.getAverageTravelTimeSeconds({
+        routeId: route.id,
+        fromStopId: stop1.id,
+        toStopId: stop2.id,
+      }, {
+        from: new Date(2025, 0, 2, 11, 0, 0),
+        to: new Date(2025, 0, 2, 13, 0, 0),
+      });
+      expect(averageTravelTime).toBeUndefined();
+    });
+  });
 });