Look at routes instead of ID for SL.

lib/signs/bus.ex

@@ -9,6 +9,7 @@ defmodule Signs.Bus do
   @drawbridge_minutes_spanish "152"
   @drawbridge_soon_spanish "157"
   @alert_levels [:station_closure, :suspension_closed_station]
+  @sl_route_ids MapSet.new(["741", "742", "743", "746"])
 
   @enforce_keys [
     :id,
@@ -140,9 +141,10 @@ defmodule Signs.Bus do
     bridge_enabled? = config_engine.chelsea_bridge_config() == :auto
     bridge_status = bridge_engine.bridge_status()
     current_time = Timex.now()
+    all_route_ids = all_route_ids(state)
 
     route_alerts_lookup =
-      for route_id <- all_route_ids(state), into: %{} do
+      for route_id <- all_route_ids, into: %{} do
         {route_id, alerts_engine.route_status(route_id)}
       end
 
@@ -167,7 +169,7 @@ defmodule Signs.Bus do
     # Compute new sign text and audio
     {[top, bottom], audios} =
       cond do
-        config_off?(id, config) ->
+        config_off?(config, all_route_ids) ->
           {["", ""], []}
 
         match?({:static_text, _}, config) ->
@@ -843,7 +845,9 @@ defmodule Signs.Bus do
   end
 
   # If a Silver Line sign is in headway mode, SignsUI will flag its predictions but RTS needs to treat it as off
-  defp config_off?("Silver_Line." <> _, :headway), do: true
-  defp config_off?(_, :off), do: true
+  defp config_off?(:headway, route_ids),
+    do: route_ids |> MapSet.new() |> MapSet.subset?(@sl_route_ids)
+
+  defp config_off?(:off, _), do: true
   defp config_off?(_, _), do: false
 end