In 1978, De Simon together with Breda Costruzioni Ferroviarie formed a new consortium called Inbus, which in the 1980s achieved a 30% share of the national bus market.

During this time, De Simon built a new construction plant in Palermo, Sicily, called IMEA, that would be the main supplier of the island for urban and interurban buses.

After the disbanding of the consortium in 1990, De Simon continued producing buses in collaboration with Iveco and Renault, introducing for the first time in Italy the bodies built from stainless steel.

Starting in 1993, De Simon focussed mainly on intercity buses built entirely from stainless steel, using chassis from European manufacturers Scania and later Mercedes-Benz.

In the urban sector, De Simon held a franchise to sell in Italy the buses of the Belgian manufacturer Van Hool, between 8 and 18 meters in length, and available even with a natural gas-powered engine.