Roll-a-ball controller
First let us nitpick a little bit.  

MoveVehicle would be a nice name for a method but for a class it isn't choosen well. A class name should be made out of a noun or a noun phrase. So for instance VehicleMover or VehicleController would be a much better name for this class.  



The method in question  


public void FixedUpdate()
{
    foreach(KeyValuePair&lt;KeyCode, Vector3&gt; keyMapping in this.keyMappings)
    {
        if(Input.GetKey(keyMapping.Key) &amp;&amp; this.IsGrounded())
        {
            Vector3 objectForce = keyMapping.Value * this.accelerationForce;
            this.rigidBody.drag = objectForce.sqrMagnitude / this.dragDividend;
            this.rigidBody.AddForce(objectForce);
        }
    }
}  



here I would suggest to use var rather than KeyValuePair&lt;KeyCode, Vector3&gt; which would make your code a little bit cleaner and its obvious that it will be a KeyValuePair&lt;TKey,TValue.  

Otherwise your code looks nice and tidy. Good job.  

I don't know Unity3D at all, so I don't know if it is possible to switch the public float accelerationForce; to a public property. If this is possible, I would suggest inside the setter to change all the values of the Dictionary so they represent the objectforce. This would involve a second kind of collection or some constants to hold the currently predifined values of the current Dictionary.  

If it is likely that the accelerationForce is called less often than the FixedUpdate() method this will speed the whole thing up.