If you wants to enable to mention vehicle number in BUSY,To enable it you can follow given steps:
Step 1:Go to the Administration menu,
Step 2:Click on Configuration,
Step 3:Click Voucher series Configuration,
Step 4:Click sales and select series,
Step 5:Click voucher configuration,Here you can find an option is Input Transport Details,Specify Y,then save.
Step 6:Now you can go and add transaction,while saving a voucher the transport window will appear,here you can enter vehicle number and other transport Details.