Hi,
Please note that, in arcgis network analyst, when you are building a network. It is possible to define a separate penalty for each direction of travel on the same link (line segment). Therefore, for each link you can make a FT_penalty (from_node-to-to_node penalty) and a TF_penalty (to_node-to-from_node penalty). In your case you could give a penalty to direction from street to bus, but not from bus to street.
You must have two separate fields, one for each direction, in your attribute table. You can then define them into the model when you are defining 'evaluators' while building the network.
regards,