diff --git a/src/saveload/tunnel_sl.cpp b/src/saveload/tunnel_sl.cpp
index 310b25a0b2..470de84590 100644
--- a/src/saveload/tunnel_sl.cpp
+++ b/src/saveload/tunnel_sl.cpp
@@ -41,6 +41,7 @@ static void Load_TUNN()
 	while ((index = SlIterateArray()) != -1) {
 		Tunnel *tunnel = new (index) Tunnel();
 		SlObject(tunnel, _tunnel_desc);
+		tunnel->UpdateIndexes();
 	}
 }
 
diff --git a/src/tunnel_base.h b/src/tunnel_base.h
index 6d088bb8f3..92408abde8 100644
--- a/src/tunnel_base.h
+++ b/src/tunnel_base.h
@@ -17,7 +17,7 @@
 
 struct Tunnel;
 
-typedef Pool<Tunnel, TunnelID, 64, 64000> TunnelPool;
+typedef Pool<Tunnel, TunnelID, 64, 1048576> TunnelPool;
 extern TunnelPool _tunnel_pool;
 
 struct Tunnel : TunnelPool::PoolItem<&_tunnel_pool> {
@@ -27,13 +27,21 @@ struct Tunnel : TunnelPool::PoolItem<&_tunnel_pool> {
 	bool is_chunnel;
 
 	Tunnel() {}
-	Tunnel(TileIndex tile_n, TileIndex tile_s, bool is_chunnel) : tile_n(tile_n), tile_s(tile_s), is_chunnel(is_chunnel) {}
 	~Tunnel();
 
+	Tunnel(TileIndex tile_n, TileIndex tile_s, bool is_chunnel) : tile_n(tile_n), tile_s(tile_s), is_chunnel(is_chunnel)
+	{
+		this->UpdateIndexes();
+	}
+
+	void UpdateIndexes();
+
 	static inline Tunnel *GetByTile(TileIndex tile)
 	{
 		return Tunnel::Get(GetTunnelIndex(tile));
 	}
+
+	static void PreCleanPool();
 };
 
 #define FOR_ALL_TUNNELS_FROM(var, start) FOR_ALL_ITEMS_FROM(Tunnel, tunnel_index, var, start)
diff --git a/src/tunnel_map.cpp b/src/tunnel_map.cpp
index 5ffb409c47..cd049f7397 100644
--- a/src/tunnel_map.cpp
+++ b/src/tunnel_map.cpp
@@ -13,6 +13,7 @@
 #include "tunnelbridge_map.h"
 
 #include "core/pool_func.hpp"
+#include <unordered_map>
 
 #include "safeguards.h"
 
@@ -20,12 +21,45 @@
 TunnelPool _tunnel_pool("Tunnel");
 INSTANTIATE_POOL_METHODS(Tunnel)
 
+static std::unordered_map<TileIndex, TunnelID> tunnel_tile_index_map;
+
 /**
  * Clean up a tunnel tile
  */
 Tunnel::~Tunnel()
 {
 	if (CleaningPool()) return;
+
+	if (this->index >= TUNNEL_ID_MAP_LOOKUP) {
+		tunnel_tile_index_map.erase(this->tile_n);
+		tunnel_tile_index_map.erase(this->tile_s);
+	}
+}
+
+/**
+ * Update tunnel indexes
+ */
+void Tunnel::UpdateIndexes()
+{
+	if (this->index >= TUNNEL_ID_MAP_LOOKUP) {
+		tunnel_tile_index_map[this->tile_n] = this->index;
+		tunnel_tile_index_map[this->tile_s] = this->index;
+	}
+}
+
+/**
+ * Tunnel pool is about to be cleaned
+ */
+void Tunnel::PreCleanPool()
+{
+	tunnel_tile_index_map.clear();
+}
+
+TunnelID GetTunnelIndexByLookup(TileIndex t)
+{
+	auto iter = tunnel_tile_index_map.find(t);
+	assert_msg(iter != tunnel_tile_index_map.end(), "tile: 0x%X", t);
+	return iter->second;
 }
 
 /**
diff --git a/src/tunnel_map.h b/src/tunnel_map.h
index b684437057..55f6ce7eea 100644
--- a/src/tunnel_map.h
+++ b/src/tunnel_map.h
@@ -14,7 +14,9 @@
 
 #include "road_map.h"
 
-typedef uint16 TunnelID; ///< Type for the unique identifier of tunnels.
+typedef uint32 TunnelID; ///< Type for the unique identifier of tunnels.
+
+static const TunnelID TUNNEL_ID_MAP_LOOKUP = 0xFFFF; ///< Sentinel ID value to store in m2 to indiciate that the ID should be looked up instead
 
 /**
  * Is this a tunnel (entrance)?
@@ -46,8 +48,11 @@ static inline bool IsTunnelTile(TileIndex t)
  */
 static inline TunnelID GetTunnelIndex(TileIndex t)
 {
+	extern TunnelID GetTunnelIndexByLookup(TileIndex t);
+
 	assert(IsTunnelTile(t));
-	return _m[t].m2;
+	TunnelID map_id = _m[t].m2;
+	return map_id == TUNNEL_ID_MAP_LOOKUP ? GetTunnelIndexByLookup(t) : map_id;
 }
 
 TileIndex GetOtherTunnelEnd(TileIndex);
@@ -65,7 +70,7 @@ static inline void MakeRoadTunnel(TileIndex t, Owner o, TunnelID id, DiagDirecti
 {
 	SetTileType(t, MP_TUNNELBRIDGE);
 	SetTileOwner(t, o);
-	_m[t].m2 = id;
+	_m[t].m2 = (id >= TUNNEL_ID_MAP_LOOKUP) ? TUNNEL_ID_MAP_LOOKUP : id;
 	_m[t].m3 = 0;
 	_m[t].m4 = 0;
 	_m[t].m5 = TRANSPORT_ROAD << 2 | d;
@@ -88,7 +93,7 @@ static inline void MakeRailTunnel(TileIndex t, Owner o, TunnelID id, DiagDirecti
 {
 	SetTileType(t, MP_TUNNELBRIDGE);
 	SetTileOwner(t, o);
-	_m[t].m2 = id;
+	_m[t].m2 = (id >= TUNNEL_ID_MAP_LOOKUP) ? TUNNEL_ID_MAP_LOOKUP : id;
 	SB(_m[t].m1, 7, 1, GB(r, 4, 1));
 	SB(_m[t].m3, 0, 4, GB(r, 0, 4));
 	SB(_m[t].m3, 4, 4, 0);