diff --git a/src/repositories/ApiBasedRepository.ts b/src/repositories/ApiBasedRepository.ts
index 18a562e..dda591a 100644
--- a/src/repositories/ApiBasedRepository.ts
+++ b/src/repositories/ApiBasedRepository.ts
@@ -8,11 +8,11 @@ export interface ApiBasedRepositoryCache {
   etasForStopId?: {
     [stopId: string]: IEta[],
   },
-  stopsBySystemId?: {
-    [systemId: string]: IStop[],
+  stopsByStopId?: {
+    [stopId: string]: IStop,
   },
-  shuttlesByShuttleId?: {
-    [shuttleId: string]: IShuttle[],
+  shuttleByShuttleId?: {
+    [shuttleId: string]: IShuttle,
   },
   // To speed things up, implement caches for other data later
 }
@@ -34,6 +34,7 @@ const defaultTtls: ApiBasedRepositoryMillisecondTTLs = {
 
 export class ApiBasedRepository implements GetterRepository {
   constructor(
+    private systemId: string,
     private initialCache: ApiBasedRepositoryCache | undefined = emptyCache,
     private ttls: ApiBasedRepositoryMillisecondTTLs = defaultTtls,
   ) {
diff --git a/test/repositories/ApiBasedRepositoryTests.test.ts b/test/repositories/ApiBasedRepositoryTests.test.ts
index 26e749e..52947a7 100644
--- a/test/repositories/ApiBasedRepositoryTests.test.ts
+++ b/test/repositories/ApiBasedRepositoryTests.test.ts
@@ -149,7 +149,7 @@ describe("getEtaForShuttleAndStopId", () => {
   test("getEtaForShuttleAndStopId returns correct ETA data", async () => {
     updateGlobalFetchMockJson(genericEtaDataByStopId);
 
-    const repository = new ApiBasedRepository();
+    const repository = new ApiBasedRepository("1");
     const result = await repository.getEtaForShuttleAndStopId("5577", "177666");
 
     expect(result?.secondsRemaining).toEqual(587);
@@ -157,7 +157,7 @@ describe("getEtaForShuttleAndStopId", () => {
   });
 
   test("getEtaForShuttleAndStopId returns null if API call is invalid and cache is empty", async () => {
-    const repository = new ApiBasedRepository();
+    const repository = new ApiBasedRepository("1");
     const result = await repository.getEtaForShuttleAndStopId("5577", "177666");
 
     expect(result).toEqual(null);
@@ -190,7 +190,7 @@ describe("getEtasForShuttleId", () => {
       etasForStopId: 100000,
     };
 
-    const repository = new ApiBasedRepository(initialCache, ttls);
+    const repository = new ApiBasedRepository("1", initialCache, ttls);
     repository.updateEtasForSystemIfTTL = jest.fn(async () => {
     });
     const result = await repository.getEtasForShuttleId("5577");
@@ -199,7 +199,7 @@ describe("getEtasForShuttleId", () => {
   });
 
   test("getEtasForShuttleId returns empty array if no data available", async () => {
-    const repository = new ApiBasedRepository();
+    const repository = new ApiBasedRepository("1");
     repository.updateEtasForSystemIfTTL = jest.fn(async () => {
     });
     const result = await repository.getEtasForShuttleId("5577");
@@ -234,7 +234,7 @@ describe("getEtasForStopId", () => {
       etasForStopId: 100000,
     };
 
-    const repository = new ApiBasedRepository(initialCache, ttls);
+    const repository = new ApiBasedRepository("1", initialCache, ttls);
     repository.updateEtasForSystemIfTTL = jest.fn(async () => {
     });
     const result = await repository.getEtasForStopId("177666");
@@ -243,7 +243,7 @@ describe("getEtasForStopId", () => {
   });
 
   test("getEtasForStopId returns empty array if no data available", async () => {
-    const repository = new ApiBasedRepository();
+    const repository = new ApiBasedRepository("1");
     repository.updateEtasForSystemIfTTL = jest.fn(async () => {
     });
     const result = await repository.getEtasForShuttleId("5577");
@@ -275,20 +275,18 @@ describe("updateEtasForSystemIfTTL", () => {
           expectedEta,
         ],
       },
-      stopsBySystemId: {
-        "1": [
-          {
-            systemId: "1",
-            millisecondsSinceEpoch: Date.now() - 1000,
-            name: "Chapman Court",
-            id: "177666",
-            coordinates: {
-              latitude: 33.796796,
-              longitude: -117.889293
-            },
-          }
-        ],
-      },
+      stopsByStopId: {
+        "1": {
+          systemId: "1",
+          millisecondsSinceEpoch: Date.now() - 1000,
+          name: "Chapman Court",
+          id: "177666",
+          coordinates: {
+            latitude: 33.796796,
+            longitude: -117.889293
+          },
+        }
+      }
     };
 
     const ttls: ApiBasedRepositoryMillisecondTTLs = {
@@ -296,7 +294,7 @@ describe("updateEtasForSystemIfTTL", () => {
       etasForStopId: 100000,
     };
 
-    const repository = new ApiBasedRepository(initialCache, ttls);
+    const repository = new ApiBasedRepository("1", initialCache, ttls);
     await repository.updateEtasForSystemIfTTL("1");
 
     const updatedResult = await repository.getEtaForShuttleAndStopId(
@@ -309,7 +307,7 @@ describe("updateEtasForSystemIfTTL", () => {
   test("updateEtasForSystemIfTTL updates all ETA data if data is TTL", async () => {
     updateGlobalFetchMockJson(genericEtaDataByStopId);
 
-    const repository = new ApiBasedRepository();
+    const repository = new ApiBasedRepository("1");
     repository.getStopsBySystemId = jest.fn(async () => {
       return [
         {