@@ -112,15 +112,7 @@ defmodule Dotcom.TripPlan.Helpers do
   def route_line_name(route) do
     route
     |> mbta_id()
-    |> case do
-      "Mattapan" -> "mattapan-line"
-      "Red" -> "red-line"
-      "Green" -> "green-line"
-      "Green-" <> branch -> "green-line-#{String.downcase(branch)}"
-      "Blue" -> "blue-line"
-      "Orange" -> "orange-line"
-      _ -> nil
-    end
+    |> Routes.Route.subway_line_name()
   end
 
   # Icons we know we have SVGs for, modify if new icons are added/removed
 
@@ -33,7 +33,7 @@ defmodule DotcomWeb.RouteComponents do
   end
 
   def route_icon(%{route: %Route{id: route_id}} = assigns) do
-    case line_name(route_id) do
+    case Route.subway_line_name(route_id) do
       nil ->
         ~H"""
         <SystemIcons.route_icon name={@route.name} size={@size} {@rest} />
@@ -48,18 +48,6 @@ defmodule DotcomWeb.RouteComponents do
     end
   end
 
-  defp line_name(route_id) do
-    case route_id do
-      "Mattapan" -> "mattapan-line"
-      "Red" -> "red-line"
-      "Green" -> "green-line"
-      "Green-" <> branch -> "green-line-#{String.downcase(branch)}"
-      "Blue" -> "blue-line"
-      "Orange" -> "orange-line"
-      _ -> nil
-    end
-  end
-
   slot :inner_block
 
   @doc """
 
@@ -72,7 +72,7 @@ defmodule DotcomWeb.Components.SearchHits do
   end
 
   defp hit_icon(%{hit: %{"index" => "routes", "route" => route}} = assigns) do
-    line_name = hit_route_line_name(route)
+    line_name = Routes.Route.subway_line_name(route["id"])
 
     cond do
       not is_nil(line_name) ->
@@ -221,18 +221,6 @@ defmodule DotcomWeb.Components.SearchHits do
 
   defp hit_highlight(_), do: nil
 
-  defp hit_route_line_name(%{"id" => route_id}) do
-    case route_id do
-      "Mattapan" -> "mattapan-line"
-      "Red" -> "red-line"
-      "Green" -> "green-line"
-      "Green-" <> branch -> "green-line-#{String.downcase(branch)}"
-      "Blue" -> "blue-line"
-      "Orange" -> "orange-line"
-      _ -> nil
-    end
-  end
-
   defp transit_name("CR-" <> _), do: "commuter-rail"
   defp transit_name("local_bus"), do: "bus"
 
 
@@ -185,10 +185,6 @@ defmodule DotcomWeb.ProjectsPageLive do
     Enum.uniq_by(routes, &route_to_mode_name/1)
   end
 
-  def bus_name(id) do
-    if Routes.Route.silver_line?(id), do: "silver-line", else: "bus"
-  end
-
   def route_to_mode_name(%{mode: "subway", id: id}) do
     cond do
       Regex.run(~r/^green/i, id) ->
@@ -207,7 +203,7 @@ defmodule DotcomWeb.ProjectsPageLive do
 
   def route_to_mode_name(%{mode: "commuter_rail"}), do: "commuter-rail"
   def route_to_mode_name(%{mode: "ferry"}), do: "ferry"
-  def route_to_mode_name(%{id: id}), do: bus_name(id)
+  def route_to_mode_name(%{id: id}), do: Routes.Route.line_name(id) || "bus"
 
   attr :route, :any, required: true
   attr :size, :string, default: "default"
 
@@ -139,6 +139,32 @@ defmodule Routes.Route do
   def types_for_mode(:mattapan_line), do: [0]
   def types_for_mode(:silver_line), do: [3]
 
+  @doc """
+  The `MbtaMetro` route icon line name (e.g. `"green-line-b"`) for a subway line
+  route ID, or `nil` if the ID is not a subway line.
+  """
+  @spec subway_line_name(id_t() | nil) :: String.t() | nil
+  def subway_line_name("Mattapan"), do: "mattapan-line"
+  def subway_line_name("Red"), do: "red-line"
+  def subway_line_name("Green"), do: "green-line"
+  def subway_line_name("Green-" <> branch), do: "green-line-#{String.downcase(branch)}"
+  def subway_line_name("Blue"), do: "blue-line"
+  def subway_line_name("Orange"), do: "orange-line"
+  def subway_line_name(_), do: nil
+
+  @doc """
+  Like `subway_line_name/1`, but also returns `"silver-line"` for Silver Line
+  route IDs.
+  """
+  @spec line_name(id_t() | nil) :: String.t() | nil
+  def line_name(id) do
+    if silver_line?(id) do
+      "silver-line"
+    else
+      subway_line_name(id)
+    end
+  end
+
   @spec icon_atom(t) :: gtfs_route_type | subway_lines_type
   def icon_atom(%__MODULE__{external_agency_name: "Massport"}), do: :massport_shuttle
   def icon_atom(%__MODULE__{external_agency_name: "Logan Express"}), do: :logan_express
 
@@ -238,6 +238,51 @@ defmodule Routes.RouteTest do
     end
   end
 
+  describe "subway_line_name/1" do
+    test "returns the icon name for each subway line" do
+      for {id, name} <- [
+            {"Red", "red-line"},
+            {"Orange", "orange-line"},
+            {"Blue", "blue-line"},
+            {"Mattapan", "mattapan-line"},
+            {"Green", "green-line"}
+          ] do
+        assert subway_line_name(id) == name
+      end
+    end
+
+    test "returns the icon name for each Green Line branch" do
+      for branch <- ~w(B C D E) do
+        assert subway_line_name("Green-#{branch}") == "green-line-#{String.downcase(branch)}"
+      end
+    end
+
+    test "returns nil for routes that aren't subway lines" do
+      for id <- ["1", "741", "CR-Providence", "Boat-F1", "", nil] do
+        assert subway_line_name(id) == nil
+      end
+    end
+  end
+
+  describe "line_name/1" do
+    test "returns subway line icon names" do
+      assert line_name("Red") == "red-line"
+      assert line_name("Green-C") == "green-line-c"
+    end
+
+    test "returns silver-line for Silver Line routes" do
+      for id <- Route.silver_line() do
+        assert line_name(id) == "silver-line"
+      end
+    end
+
+    test "returns nil for other routes" do
+      for id <- ["1", "CR-Providence", "Boat-F1", nil] do
+        assert line_name(id) == nil
+      end
+    end
+  end
+
   describe "hidden?/1" do
     test "Returns true for hidden routes" do
       hidden_routes = [