The InterBus is one of the more successful joint ventures the empires have undertaken. It was formed some 30 years ago to act as a neutral passenger transportation company that would span the entire known world. Since then it has evolved a bit, especially when it started to ferry goods too.
The InterBus is used by the SCC to ferry goods between stations, as they are reliable and operate in every station in the world. As InterBus has to operate not only in empire stations, but also in pirate havens and other stations associated with organized crime, the company has to uphold a very strict policy regarding neutrality and secrecy.
Even if the company is owned by the empires, no information regarding to shipments or station locations is ever given out. The strict adherence to these rules has allowed InterBus to operate without harassment in every corner of the world of EVE, making them one of the pillars of the inter-stellar community.