Well if you have the bridge module, Define your lanes, then add your vehicles, add a vehicle class, add an Analysis case for moving load type case and specify the vehicle class (usually take the default). This will give you your influence lines, surfaces, min/max load envelopes, etc.
Also, there is another type of moving load option called multi-step static load which you can use by going to Define menu> Load cases> then add a load case 'Moving load' type and you will be prompted to input additional data..Make sure you then add an Analysis case for Multi-step static.. this multi-step static lets you to march across several permit vehicles or whatever you want going in both directions