There are subsidies, which should primarily be offered to poor companies, to get them started.
The new stuff: offer the companies some "contract" or "missions". If you succeed in the given time, you get your money and everything is fine. But, even more important: if you don't succeed, you get a penalty for breaking the contract. Maybe this penalty depends on the companies' wealth.
Example: being owner of a rich company, you get a message during the game (not known to the other companies):
"New Contract Offered:
- Create an Airport in New York.
- Push LA to 15'000.
- employ 50 trains at least.
- transport 30'000 passengers
until Mai 1970. Your rewards will be:
- 10'000 cash in hand
If you break contract (that is, if you don't succeed in the given time), you will loose 50% off your liquid money." Accept Decline
Of course a company can have several missions running in parallel... if they want so ;)