Hi Cindy,
Purchase info records create Transportation lanes in SNC system.
Transportation Lanes are required for SNC and SNC understands it as a relation ship between plant & Supplier.
You can also check if External procurement relationship is created after you send PIR to SNC through CIF. T-code for ext. procurement relation ship is /SAPAPO/PWBSRC1 - Maintain Ext. Proc. Relationships.
As mentioned by Selim, other source of creating T-lanes in SNC are Contracts & scheduling agreements.
Regards,
Rahul Sharma