The correct bus types should now be spawned

HarmonyPatches/BuildingManagerPatches/GetDepotLevelsPatch.cs

@@ -0,0 +1,42 @@
+using ColossalFramework;
+using ImprovedPublicTransport2.HarmonyPatches.DepotAIPatches;
+using ImprovedPublicTransport2.Util;
+
+namespace ImprovedPublicTransport2.HarmonyPatches.BuildingManagerPatches
+{
+    public static class GetDepotLevelsPatch
+    {
+        public static void Apply()
+        {
+            PatchUtil.Patch(
+                new PatchUtil.MethodDefinition(typeof(BuildingManager), nameof(BuildingManager.GetDepotLevels)),
+                new PatchUtil.MethodDefinition(typeof(GetDepotLevelsPatch), nameof(Prefix)),
+                null
+            );
+        }
+
+        public static void Undo()
+        {
+            PatchUtil.Unpatch(
+                new PatchUtil.MethodDefinition(typeof(BuildingManager), nameof(BuildingManager.GetDepotLevels))
+            );
+        }
+
+        private static bool Prefix(ref TransportLine.DepotLevels __result, ushort lineID)
+        {
+            var info1 = Singleton<TransportManager>.instance.m_lines.m_buffer[lineID].Info;
+            if (info1 == null || info1.GetSubService() != ItemClass.SubService.PublicTransportBus ||
+                info1.GetClassLevel() != ItemClass.Level.Level1)
+            {
+                return true;
+            }
+            __result = new TransportLine.DepotLevels()
+            {
+                m_level1 = true,
+                m_level2 = true
+            };
+            return false;
+
+        }
+    }
+}

HarmonyPatches/DepotAIPatches/ClassMatchesPatch.cs

@@ -0,0 +1,36 @@
+using ImprovedPublicTransport2.Util;
+
+namespace ImprovedPublicTransport2.HarmonyPatches.DepotAIPatches
+{
+    public static class ClassMatchesPatch
+    {
+
+        public static void Apply()
+        {
+            PatchUtil.Patch(
+                new PatchUtil.MethodDefinition(typeof(DepotAI), "ClassMatches"),
+                new PatchUtil.MethodDefinition(typeof(ClassMatchesPatch),
+                    nameof(Prefix))
+            );
+        }
+
+        public static void Undo()
+        {
+            PatchUtil.Unpatch(
+                new PatchUtil.MethodDefinition(typeof(DepotAI), "ClassMatches")
+            );
+        }
+
+        private static bool Prefix(ref bool __result, ItemClass itemClass, ItemClass otherItemClass)
+        {
+            if (itemClass.m_subService == ItemClass.SubService.PublicTransportBus 
+                && (itemClass.m_level == ItemClass.Level.Level1 || itemClass.m_level == ItemClass.Level.Level2))    
+            {
+                __result = otherItemClass.m_subService == ItemClass.SubService.PublicTransportBus && (otherItemClass.m_level == ItemClass.Level.Level1 || otherItemClass.m_level == ItemClass.Level.Level2);
+                return false;
+            }
+
+            return true;
+        }
+    }
+}

HarmonyPatches/TransportManagerPatches/CheckTransportLineVehiclesPatch.cs

@@ -0,0 +1,31 @@
+using ImprovedPublicTransport2.Util;
+
+namespace ImprovedPublicTransport2.HarmonyPatches.TransportManagerPatches
+{
+    public static class CheckTransportLineVehiclesPatch
+    {
+        public static void Apply()
+        {
+            PatchUtil.Patch(
+                new PatchUtil.MethodDefinition(typeof(TransportManager),
+                    nameof(TransportManager.CheckTransportLineVehicles)),
+                new PatchUtil.MethodDefinition(typeof(CheckTransportLineVehiclesPatch),
+                    nameof(Prefix))
+            );
+        }
+
+        public static void Undo()
+        {
+            PatchUtil.Unpatch(
+                new PatchUtil.MethodDefinition(typeof(TransportManager),
+                    nameof(TransportManager.CheckTransportLineVehicles))
+            );
+        }
+
+        public static bool Prefix()
+        {
+
+            return false; //we don't want to despawn buses of the 'wrong type'
+        }
+    }
+}

ImprovedPublicTransport.csproj

@@ -87,11 +87,14 @@
     <Compile Include="Detour\Vehicles\TramAIDetour.cs" />
     <Compile Include="Detour\Vehicles\TrolleybusAIDetour.cs" />
     <Compile Include="GameDefault.cs" />
+    <Compile Include="HarmonyPatches\BuildingManagerPatches\GetDepotLevelsPatch.cs" />
+    <Compile Include="HarmonyPatches\DepotAIPatches\ClassMatchesPatch.cs" />
     <Compile Include="HarmonyPatches\DepotAIPatches\StartTransferPatch.cs" />
     <Compile Include="HarmonyPatches\NetManagerPatches\ReleaseNodePatch.cs" />
     <Compile Include="HarmonyPatches\PublicTransportLineVehicleSelectorPatches\GetVehicleInfoPatch.cs" />
     <Compile Include="HarmonyPatches\TransportLinePatches\GetLineVehiclePatch.cs" />
     <Compile Include="HarmonyPatches\TransportLinePatches\SimulationStepPatch.cs" />
+    <Compile Include="HarmonyPatches\TransportManagerPatches\CheckTransportLineVehiclesPatch.cs" />
     <Compile Include="HarmonyPatches\VehicleManagerPatches\ReleaseWaterSourcePatch.cs" />
     <Compile Include="HarmonyPatches\XYZVehicleAIPatches\LoadPassengersPatch.cs" />
     <Compile Include="HarmonyPatches\XYZVehicleAIPatches\UnloadPassengersPatch.cs" />

ImprovedPublicTransportMod.cs

@@ -6,10 +6,12 @@
 using ImprovedPublicTransport2.Detour;
 using ImprovedPublicTransport2.Detour.Vehicles;
 using ImprovedPublicTransport2.HarmonyPatches;
+using ImprovedPublicTransport2.HarmonyPatches.BuildingManagerPatches;
 using ImprovedPublicTransport2.HarmonyPatches.DepotAIPatches;
 using ImprovedPublicTransport2.HarmonyPatches.NetManagerPatches;
 using ImprovedPublicTransport2.HarmonyPatches.PublicTransportLineVehicleSelectorPatches;
 using ImprovedPublicTransport2.HarmonyPatches.TransportLinePatches;
+using ImprovedPublicTransport2.HarmonyPatches.TransportManagerPatches;
 using ImprovedPublicTransport2.HarmonyPatches.VehicleManagerPatches;
 using ImprovedPublicTransport2.HarmonyPatches.XYZVehicleAIPatches;
 using ImprovedPublicTransport2.OptionsFramework.Extensions;
@@ -91,6 +93,9 @@ public override void OnLevelLoaded(LoadMode mode)
           ReleaseNodePatch.Apply();
           ReleaseWaterSourcePatch.Apply();
           GetVehicleInfoPatch.Apply();
+          CheckTransportLineVehiclesPatch.Apply();
+          ClassMatchesPatch.Apply();
+          GetDepotLevelsPatch.Apply();
 
           Redirector<BusAIDetour>.Deploy();
           Redirector<TrolleybusAIDetour>.Deploy();
@@ -176,7 +181,10 @@ private void Deinit()
       ReleaseNodePatch.Undo();
       ReleaseWaterSourcePatch.Undo();
       GetVehicleInfoPatch.Undo();
-
+      ClassMatchesPatch.Undo();
+      CheckTransportLineVehiclesPatch.Undo();
+      GetDepotLevelsPatch.Undo();
+
       Redirector<TramAIDetour>.Revert();
       Redirector<PassengerTrainAIDetour>.Revert();
       Redirector<PassengerShipAIDetour>.Revert();