Bing maps: how to display "See best route based on traffic" after direction request?

Question regarding Bing Maps v7. How to display link "See best route based on traffic" after direction request. It seems to set some option in 'DirectionsRequestOptions' but I don't know what exactly. See example here http://www.bingmapsportal.com/isdk/ajaxv7#DirectionsMo开发者_Python百科dule2 Thank you

It displays automatically by Bing Maps, if "best route" is exist for entered address.