diff --git a/client/src/components/Map/valhallaRoute.test.ts b/client/src/components/Map/valhallaRoute.test.ts
index c4e760f26..64f63f013 100644
--- a/client/src/components/Map/valhallaRoute.test.ts
+++ b/client/src/components/Map/valhallaRoute.test.ts
@@ -793,4 +793,56 @@ describe('through the TREK services (routing relay)', () => {
     expect(bodies[0]).not.toHaveProperty('shape')
     expect(bodies[0]).toMatchObject({ encoded_polyline: expect.any(String), costing: 'bicycle', shape_match: 'map_snap' })
   })
+
+  it('VALHALLA-RELAY-006: reads a 400 without error_code, and a route the server does not have, as the relay unable to answer', async () => {
+    const refusals = [
+      () => HttpResponse.json({ error: 'Expected number, received string' }, { status: 400 }),
+      () => new HttpResponse('Not Found', { status: 404 }),
+      () => HttpResponse.json({ error: 'Method Not Allowed' }, { status: 405 }),
+    ]
+    for (const refusal of refusals) {
+      resetValhallaTurns()
+      let fossgis = 0
+      server.use(
+        http.post(RELAY, refusal),
+        http.post(FOSSGIS_VALHALLA, () => { fossgis++; return HttpResponse.json(answer()) }),
+      )
+      await expect(valhallaRouteAvoiding(HAMBURG, BERLIN, 'driving', 'toll')).resolves.not.toBeNull()
+      expect(fossgis).toBe(1)
+      expect(valhallaBase()).toBe('https://valhalla1.openstreetmap.de')
+    }
+  })
+
+  it('VALHALLA-RELAY-007: rests the relay as long as its Retry-After says, at most an hour', async () => {
+    for (const [retryAfter, restMs] of [['30', 30_000], ['86400', 60 * 60_000]] as const) {
+      resetValhallaTurns()
+      server.use(
+        http.post(RELAY, () => HttpResponse.json({ error: 'spent' }, { status: 429, headers: { 'Retry-After': retryAfter } })),
+        http.post(FOSSGIS_VALHALLA, () => HttpResponse.json(answer())),
+      )
+      await valhallaRouteAvoiding(HAMBURG, BERLIN, 'driving', 'toll')
+      vi.useFakeTimers({ toFake: ['Date'] })
+      vi.setSystemTime(Date.now() + restMs - 1000)
+      expect(valhallaBase()).toBe('https://valhalla1.openstreetmap.de')
+      vi.setSystemTime(Date.now() + 2000)
+      expect(valhallaBase()).toBe(TREK_VALHALLA)
+      vi.useRealTimers()
+    }
+  })
+
+  it('VALHALLA-RELAY-008: gives up on a relay that does not answer in time and asks FOSSGIS', async () => {
+    const timeout = AbortSignal.timeout.bind(AbortSignal)
+    const spy = vi.spyOn(AbortSignal, 'timeout').mockImplementation(ms =>
+      ms === 12_000 ? AbortSignal.abort(new DOMException('signal timed out', 'TimeoutError')) : timeout(ms))
+    let fossgis = 0
+    server.use(
+      http.post(RELAY, () => HttpResponse.json(answer())),
+      http.post(FOSSGIS_VALHALLA, () => { fossgis++; return HttpResponse.json(answer()) }),
+    )
+    await expect(valhallaRouteAvoiding(HAMBURG, BERLIN, 'driving', 'toll')).resolves.not.toBeNull()
+    expect(spy).toHaveBeenCalledWith(12_000)
+    expect(fossgis).toBe(1)
+    expect(valhallaBase()).toBe('https://valhalla1.openstreetmap.de')
+    spy.mockRestore()
+  })
 })
diff --git a/client/src/components/Map/valhallaRoute.ts b/client/src/components/Map/valhallaRoute.ts
index 57934fc61..d9180a5b7 100644
--- a/client/src/components/Map/valhallaRoute.ts
+++ b/client/src/components/Map/valhallaRoute.ts
@@ -52,6 +52,16 @@ const TREK_VALHALLA = '/api/routing/valhalla'
  */
 const RELAY_REST_MS = 10 * 60_000
 
+/** The longest Retry-After of the relay this tab follows; a longer one is asked about again after it. */
+const RELAY_MAX_WAIT_MS = 60 * 60_000
+
+/**
+ * How long a route or a height question may take through the relay. The server gives the
+ * TREK Valhalla ten seconds; this leaves room for its 502 to arrive first, and where the
+ * relay itself hangs, FOSSGIS answers soon after.
+ */
+const RELAY_TIMEOUT_MS = 12_000
+
 /**
  * How far Valhalla may look for a road under a point, in metres.
  *
@@ -388,22 +398,45 @@ export function resetValhallaTurns(): void {
 }
 
 /**
- * The relay's statuses that say it cannot answer for the TREK services right now: no
- * session (a shared page), no key, a body it does not take, an allowance spent, a host
- * that is down. A 400 is Valhalla's own refusal of the way and is read as such.
+ * Whether the relay's answer says it cannot answer for the TREK services right now: no
+ * session (a shared page), no key, a body it does not take, a route this server does not
+ * have yet, an allowance spent, a host that is down. A 400 that carries Valhalla's
+ * `error_code` is its own refusal of the way and is read as such; one without is the
+ * relay refusing the body.
  */
-function relayCannotAnswer(status: number): boolean {
-  return status === 401 || status === 403 || status === 413 || status === 429 || status >= 500
+async function relayCannotAnswer(response: Response): Promise<boolean> {
+  if (response.status === 400) {
+    const data: unknown = await response.clone().json().catch(() => null)
+    return typeof (data as { error_code?: unknown } | null)?.error_code !== 'number'
+  }
+  return [401, 403, 404, 405, 413, 429].includes(response.status) || response.status >= 500
+}
+
+/** The relay's Retry-After in milliseconds, as seconds or an HTTP date, or null without one. */
+function relayWait(response: Response): number | null {
+  const value = response.headers.get('Retry-After')?.trim()
+  if (!value) return null
+  if (/^\d+$/.test(value)) return Number(value) * 1000
+  const at = Date.parse(value)
+  return Number.isNaN(at) ? null : Math.max(0, at - Date.now())
 }
 
 async function askRelay(action: ValhallaRelayAction, body: object, signal?: AbortSignal): Promise<Response | null> {
+  let bounded = signal
+  // A description brings its own deadline; a route or a height gets the relay's.
+  if (action !== 'trace_attributes') {
+    const deadline = AbortSignal.timeout(RELAY_TIMEOUT_MS)
+    bounded = signal ? AbortSignal.any([signal, deadline]) : deadline
+  }
+  let wait = RELAY_REST_MS
   try {
-    const response = await valhallaRelayRepo.ask(action, body, signal)
-    if (!relayCannotAnswer(response.status)) return response
+    const response = await valhallaRelayRepo.ask(action, body, bounded)
+    if (!(await relayCannotAnswer(response))) return response
+    wait = Math.min(relayWait(response) ?? RELAY_REST_MS, RELAY_MAX_WAIT_MS)
   } catch (err) {
     if (signal?.aborted) throw err
   }
-  relayRestingUntil = Date.now() + RELAY_REST_MS
+  relayRestingUntil = Date.now() + wait
   return null
 }