It may be a little better for people who actually have employees.
The main options are a Solo 401(k) if you have no employees, a SEP IRA (Simplified Employee Pension), usually if you have no employees, and a SIMPLE IRA, a Savings Incentive Match for Employees of Small Employers.
The link for this report is on "Next Avenue", here.
There is a last piece of advise: don't count on selling your business to retire.
Remember. most taxi drivers are self-employed.