BIke script error

I have a bike and i want to make it move forward with and augmenting velocity My script is this:

 var velocity = 0.0;

    function Update () 
    {
        if(Input.GetButton("W"))
        {
            velocitat = velocity + 0.1;
            transform.position.forward * velocity;
        }
    }

The console don't tell me any errors so I don't know what to do. Can someone help me please?

Not at my Unity machine atm but... What is the 'velocitat" variable used for. Mebe it should be this:

var velocity = 0.0;

    function Update () 
    {
        if(Input.GetButton("W"))
        {
            velocitat = velocity + 0.1;
            transform.position.forward * velocitat ;
        }
    }