diff --git a/src/components/root/app-router.test.tsx b/src/components/root/app-router.test.tsx
index 4824ea7c8..8cc1fd715 100644
--- a/src/components/root/app-router.test.tsx
+++ b/src/components/root/app-router.test.tsx
@@ -2,8 +2,9 @@ import React from 'react';
 import { render } from '../../test-utils';
 import AppRouter from './app-router';
 import rootReducer from '../../redux';
-import { createMockAppStore } from '../../setupTests';
+import { createMockAppStore, createParamInLocalStorage } from '../../setupTests';
 import { screen } from '@testing-library/react';
+import rmgRuntime, { RmgEnv } from '@railmapgen/rmg-runtime';
 
 jest.mock('./app-view', () => {
     return () => (
@@ -27,36 +28,140 @@ const mockStore = createMockAppStore({
 });
 
 describe('AppRouter', () => {
-    afterEach(() => {
-        mockStore.clearActions();
-    });
+    describe('AppRouter - UAT toggle on', () => {
+        beforeEach(() => {
+            jest.spyOn(rmgRuntime, 'getEnv').mockReturnValue(RmgEnv.UAT);
+        });
 
-    it('Can render param selector view if param id is not specified', () => {
-        render(<AppRouter />, { store: mockStore, route: '/' });
+        afterEach(() => {
+            mockStore.clearActions();
+        });
 
-        const actions = mockStore.getActions();
-        expect(actions).toHaveLength(0);
+        it('Can render param selector view if param id is not specified', () => {
+            render(<AppRouter />, { store: mockStore, route: '/' });
 
-        expect(screen.getByRole('presentation', { name: 'Mock Param Selector View' })).toBeInTheDocument();
-    });
+            const actions = mockStore.getActions();
+            expect(actions).toHaveLength(0);
+
+            expect(screen.getByRole('presentation', { name: 'Mock Param Selector View' })).toBeInTheDocument();
+        });
+
+        it('Can read param from localStorage and render app view if param is not loaded', () => {
+            createParamInLocalStorage('test-id');
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
+
+            const actions = mockStore.getActions();
+            expect(actions).toContainEqual({ type: 'app/setCurrentParamId', payload: 'test-id' });
+            expect(actions).toContainEqual(expect.objectContaining({ type: 'SET_FULL_PARAM' }));
+
+            expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+        });
+
+        it('Can render param selector view if no param in localStorage matches URL param ID', () => {
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id-2' });
 
-    it('Can read param from localStorage and render app view if param is not loaded', () => {
-        render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
+            // TODO
+            // expect(screen.getByRole('presentation', { name: 'Mock Param Selector View' })).toBeInTheDocument();
+        });
 
-        const actions = mockStore.getActions();
-        expect(actions).toContainEqual({ type: 'app/setCurrentParamId', payload: 'test-id' });
-        expect(actions).toContainEqual(expect.objectContaining({ type: 'SET_FULL_PARAM' }));
+        it('Can render app view if param is loaded', async () => {
+            const mockStore = createMockAppStore({
+                ...realStore,
+                app: { ...realStore.app, currentParamId: 'test-id' },
+            });
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
 
-        expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+            const actions = mockStore.getActions();
+            expect(actions).toHaveLength(0);
+
+            await screen.findByRole('presentation', { name: 'Mock App View' });
+        });
     });
 
-    it('Can render app view if param is loaded', async () => {
-        const mockStore = createMockAppStore({ ...realStore, app: { ...realStore.app, currentParamId: 'test-id' } });
-        render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
+    describe('AppRouter - PRD toggle off', () => {
+        beforeEach(() => {
+            jest.spyOn(rmgRuntime, 'getEnv').mockReturnValue(RmgEnv.PRD);
+        });
+
+        afterEach(() => {
+            mockStore.clearActions();
+            window.localStorage.clear();
+        });
+
+        it('Can generate param and render app view if param id is not specified and no param in localStorage', () => {
+            render(<AppRouter />, { store: mockStore, route: '/' });
+
+            // update redux store
+            const actions = mockStore.getActions();
+            expect(actions).toContainEqual(expect.objectContaining({ type: 'app/setCurrentParamId' }));
+            expect(actions).toContainEqual(expect.objectContaining({ type: 'SET_FULL_PARAM' }));
+
+            // route to new param id
+            const currentParamId = actions.find(action => action.type === 'app/setCurrentParamId').payload;
+            // TODO: URL search param?
+
+            expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+        });
+
+        it('Can read first param from localStorage and render app view if param id is not specified', () => {
+            createParamInLocalStorage('test-id');
+            render(<AppRouter />, { store: mockStore, route: '/' });
+
+            // update redux store
+            const actions = mockStore.getActions();
+            expect(actions).toContainEqual({ type: 'app/setCurrentParamId', payload: 'test-id' });
+            expect(actions).toContainEqual({
+                type: 'SET_FULL_PARAM',
+                fullParam: expect.objectContaining({ line_num: 'test-id' }),
+            });
+
+            // route to new param id
+            // TODO: URL search param?
+
+            expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+        });
+
+        it('Can read param from localStorage and render app view if param is not loaded', () => {
+            createParamInLocalStorage('test-id');
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
+
+            const actions = mockStore.getActions();
+            expect(actions).toContainEqual({ type: 'app/setCurrentParamId', payload: 'test-id' });
+            expect(actions).toContainEqual(expect.objectContaining({ type: 'SET_FULL_PARAM' }));
+
+            // TODO: URL search param?
+
+            expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+        });
+
+        it('Can read first param from localStorage and render app selector view if no param in localStorage matches URL param ID', () => {
+            createParamInLocalStorage('test-id-1');
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id-2' });
+
+            // update redux store
+            const actions = mockStore.getActions();
+            expect(actions).toContainEqual({ type: 'app/setCurrentParamId', payload: 'test-id-1' });
+            expect(actions).toContainEqual({
+                type: 'SET_FULL_PARAM',
+                fullParam: expect.objectContaining({ line_num: 'test-id-1' }),
+            });
+
+            // TODO: URL search param?
+
+            expect(screen.getByRole('presentation', { name: 'Mock App View' })).toBeInTheDocument();
+        });
+
+        it('Can render app view if param is loaded', async () => {
+            const mockStore = createMockAppStore({
+                ...realStore,
+                app: { ...realStore.app, currentParamId: 'test-id' },
+            });
+            render(<AppRouter />, { store: mockStore, route: '/?project=test-id' });
 
-        const actions = mockStore.getActions();
-        expect(actions).toHaveLength(0);
+            const actions = mockStore.getActions();
+            expect(actions).toHaveLength(0);
 
-        await screen.findByRole('presentation', { name: 'Mock App View' });
+            await screen.findByRole('presentation', { name: 'Mock App View' });
+        });
     });
 });
diff --git a/src/components/root/app-router.tsx b/src/components/root/app-router.tsx
index a01ee29a5..82e343f01 100644
--- a/src/components/root/app-router.tsx
+++ b/src/components/root/app-router.tsx
@@ -2,16 +2,18 @@ import React, { useEffect, useState } from 'react';
 import { useSearchParams } from 'react-router-dom';
 import AppView from './app-view';
 import { useRootDispatch, useRootSelector } from '../../redux';
-import rmgRuntime from '@railmapgen/rmg-runtime';
+import rmgRuntime, { RmgEnv } from '@railmapgen/rmg-runtime';
 import { LanguageCode } from '@railmapgen/rmg-translate';
 import ParamSelectorView from './param-selector-view';
 import { readParam } from '../../redux/app/action';
+import { getParamMap } from '../../util/param-manager-utils';
+import { nanoid } from 'nanoid';
 
 export default function AppRouter() {
     const dispatch = useRootDispatch();
 
     const { currentParamId } = useRootSelector(state => state.app);
-    const [searchParams] = useSearchParams();
+    const [searchParams, setSearchParams] = useSearchParams();
     const paramId = searchParams.get('project');
 
     const [isLoaded, setIsLoaded] = useState(false);
@@ -20,16 +22,34 @@ export default function AppRouter() {
         console.log('searchParam: project=' + paramId);
         if (paramId) {
             if (paramId === currentParamId) {
+                console.log('AppRouter:: Store param ID matches URL param ID. Rendering app view...');
                 setIsLoaded(true);
             } else {
-                console.warn(
-                    'AppRouter:: URL param ID does not match store param ID. Reading param with ID=' + paramId
-                );
+                if (rmgRuntime.getEnv() === RmgEnv.PRD) {
+                    const paramMap = getParamMap();
+                    const paramIds = Object.keys(paramMap);
+                    if (paramIds.length && !paramIds.includes(paramId)) {
+                        console.warn(
+                            'AppRouter:: URL param ID does not exist in localStorage. Reset to first param in localStorage in PRD env.'
+                        );
+                        const paramMap = getParamMap();
+                        setSearchParams({ project: Object.keys(paramMap)[0] });
+                        return;
+                    }
+                }
+
+                console.log(`AppRouter:: Reading param (ID=${paramId}) from localStorage`);
                 dispatch(readParam(paramId, rmgRuntime.getLanguage() as LanguageCode));
                 setIsLoaded(true);
             }
         } else {
-            console.log('AppRouter:: Render param selector');
+            if (rmgRuntime.getEnv() === RmgEnv.PRD) {
+                console.log('AppRouter:: Redirect to first param in localStorage in PRD env');
+                const paramMap = getParamMap();
+                setSearchParams({ project: Object.keys(paramMap)[0] ?? nanoid() });
+            } else {
+                console.log('AppRouter:: No URL param ID provided. Rendering param selector view...');
+            }
         }
     }, [paramId]);
 
diff --git a/src/components/root/param-selector-view.test.tsx b/src/components/root/param-selector-view.test.tsx
index cc3bb3034..9af8dc18e 100644
--- a/src/components/root/param-selector-view.test.tsx
+++ b/src/components/root/param-selector-view.test.tsx
@@ -2,25 +2,16 @@ import React from 'react';
 import { render } from '../../test-utils';
 import ParamSelectorView from './param-selector-view';
 import rootReducer from '../../redux';
-import { createMockAppStore } from '../../setupTests';
-import { initParam } from '../../redux/param/util';
-import { LocalStorageKey, RmgStyle } from '../../constants/constants';
-import { LanguageCode } from '@railmapgen/rmg-translate';
+import { createMockAppStore, createParamInLocalStorage } from '../../setupTests';
 import { fireEvent, screen } from '@testing-library/react';
 
 const realStore = rootReducer.getState();
 const mockStore = createMockAppStore({ ...realStore });
 
-const generateParamInLocalStorage = (id: string) => {
-    const rmgParam = initParam(RmgStyle.MTR, LanguageCode.English);
-    rmgParam.line_num = id;
-    window.localStorage.setItem(LocalStorageKey.PARAM_BY_ID + id, JSON.stringify(rmgParam));
-};
-
 describe('ParamSelectorView', () => {
     it('Can render view with list of projects as expected', () => {
-        generateParamInLocalStorage('test-1');
-        generateParamInLocalStorage('test-2');
+        createParamInLocalStorage('test-1');
+        createParamInLocalStorage('test-2');
 
         render(<ParamSelectorView />, { store: mockStore, route: '/' });
 
diff --git a/src/setupProxy.js b/src/setupProxy.js
index 922afb52a..9fb65fece 100644
--- a/src/setupProxy.js
+++ b/src/setupProxy.js
@@ -3,7 +3,7 @@ module.exports = app => {
         res.send({
             component: 'rmg',
             version: '9.9.9',
-            environment: 'DEV',
+            environment: 'PRD',
             instance: 'localhost',
         });
     });
diff --git a/src/setupTests.ts b/src/setupTests.ts
index d38e341e1..e2d0bc420 100644
--- a/src/setupTests.ts
+++ b/src/setupTests.ts
@@ -1,7 +1,9 @@
 import createMockStore from 'redux-mock-store';
-import { BranchStyle, StationDict } from './constants/constants';
+import { BranchStyle, LocalStorageKey, RmgStyle, StationDict } from './constants/constants';
 import rootReducer, { RootState } from './redux';
 import { getDefaultMiddleware, ThunkDispatch } from '@reduxjs/toolkit';
+import { initParam } from './redux/param/util';
+import { LanguageCode } from '@railmapgen/rmg-translate';
 
 // FIXME: any -> AnyAction?
 type DispatchExts = ThunkDispatch<RootState, void, any>;
@@ -89,3 +91,9 @@ global.fetch = (...args) => {
         return originalFetch(...args);
     }
 };
+
+export const createParamInLocalStorage = (id: string) => {
+    const rmgParam = initParam(RmgStyle.MTR, LanguageCode.English);
+    rmgParam.line_num = id;
+    window.localStorage.setItem(LocalStorageKey.PARAM_BY_ID + id, JSON.stringify(rmgParam));
+};