using System;
using System.IO;
using System.Xml.Serialization;

public class Transportation
{
    public Car[] Cars;
}

public class Car
{
    public int ID;
}

public class Test
{
    public static void Main()
    {
        Test t = new Test();
        t.SerializeObject("XmlType.xml");
    }

    // Return an XmlSerializer used for overriding.
    public XmlSerializer CreateOverrider()
    {
        // Create the XmlAttributes and XmlAttributeOverrides objects.
        XmlAttributes attrs = new XmlAttributes();
        XmlAttributeOverrides xOver = new XmlAttributeOverrides();

        /* Create an XmlTypeAttribute and change the name of the 
           XML type. */
        XmlTypeAttribute xType = new XmlTypeAttribute();
        xType.TypeName = "Autos";

        // Set the XmlTypeAttribute to the XmlType property.
        attrs.XmlType = xType;

        /* Add the XmlAttributes to the XmlAttributeOverrides,
           specifying the member to override. */
        xOver.Add(typeof(Car), attrs);

        // Create the XmlSerializer, and return it.
        XmlSerializer xSer = new XmlSerializer
        (typeof(Transportation), xOver);
        return xSer;
    }

    public void SerializeObject(string filename)
    {
        // Create an XmlSerializer instance.
        XmlSerializer xSer = CreateOverrider();

        // Create object and serialize it.
        Transportation myTransportation =
        new Transportation();

        Car c1 = new Car();
        c1.ID = 12;

        Car c2 = new Car();
        c2.ID = 44;

        myTransportation.Cars = new Car[2] { c1, c2 };

        // To write the file, a TextWriter is required.
        TextWriter writer = new StreamWriter(filename);
        xSer.Serialize(writer, myTransportation);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<Transportation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> 
  <Cars>
    <Autos>
      <ID>12</ID>
    </Autos>
    <Autos>
      <ID>44</ID>
    </Autos>
  </Cars>
</Transportation>

<?xml version="1.0" encoding="utf-8"?>
<Transportation>
  <Cars>
    <Autos>
      <ID>12</ID>
    </Autos>
    <Autos>
      <ID>44</ID>
    </Autos>
  </Cars>
</Transportation>