Make look ahead distance vaiable with speed, within a reasonable range

src/train_cmd.cpp

@@ -99,8 +99,8 @@ static bool CheckTrainStayInWormHolePathReserve(Train *t, TileIndex tile);
  *  at the current position of the train is going to be invalid */
 static DateTicksScaled GetSpeedRestrictionTimeout(const Train *t)
 {
-	const int64 look_ahead_distance = 16; // In tiles
 	const int64 velocity = std::max<int64>(25, t->cur_speed);
+	const int64 look_ahead_distance = Clamp(t->cur_speed / 8, 6, 16); // In tiles, varying between 6 and 16 depending on current speed
 
 	// This assumes travel along the X or Y map axis, not diagonally. See GetAdvanceDistance, GetAdvanceSpeed.
 	const int64 ticks_per_tile = (192 * 16 * 4 / 3) / velocity;