Federal regulators shut down 26 curbside bus operators on Thursday, including three in Philadelphia and eight elsewhere in Pennsylvania, in the largest bus safety crackdown in U.S. history.

A Philadelphia-based firm, New Century Travel, Inc., operated 10 of the lines.

The bus operation, which carried about 1,800 passengers a day along I-95 between New York and Florida, were cited for a variety of safety hazards, including drivers without valid licenses or medical certifications, buses with uninspected brakes, tires and lights, and drivers who did not get mandatory rest periods. Many of the operations are so-called Chinatown buses, which offer inexpensive rides between Asian communities in Northeast cities.

The crackdown came in a yearlong investigation after three bus accidents last year killed 21 people.

Altogether, three bus operators, with 26 subsidiaries, were ordered to cease operations immediately because they posed an "imminent hazard" to the traveling public.

By targeting companies with multiple bus operations, investigators for the Federal Motor Carrier Safety Administration were attempting to stop bus companies from simply switching names to dodge regulators, said federal Transportation Secretary Ray LaHood.

Besides New Century, Apex Bus, Inc., and I-95 Coach, Inc., both based in New York City with 16 subsidiaries, were ordered shut down.

New Century is based in Chinatown at 55 N. 11th St., according to federal safety records. A subsidiary firm, Wahoo Tour and Charter Inc., is based nearby, at 913 Wood St.

The third Philadelphia company is Universe Bus Inc., with operations at 2300 S. 9th St.

Eight other companies were closed in Pennsylvania, including New Egg Bus Inc., in State College; Asia Tours Inc., State College; All State Travel Bus Inc., ; RA Transportation Inc., Lancaster; Antai Tours Inc., Wilkes-Barre; Super Luxury Tours Inc., Wilkes-Barre; 2003 Coach Inc., Wilkes-Barre, and Fujian Tourism Co. Ltd., of Springfield, Delaware County.

Several of the operators had been ordered to cease operations before, including Super Luxury Tours, which was ordered closed last March after one of its buses crashed on the New Jersey Turnpike, killing Troy Nguyen, 21, of Royersford, and the bus driver.

Super Luxury continued to operate through New Century Travel, whose operating authority was revoked in 2010 and never reinstated.

There was no answer Thursday at the phone number listed for New Century.

A new federal rule enacted in April expands regulators' abilities to go after such "reincarnated" companies by linking all companies that are owned by the same operators.

LaHood called for Congress to approve tougher bus-safety rules in pending legislation to give regulators greater authority to pursue "reincarnated" operators and increasing the maximum penalty for violations from $2,200 a day to $25,000 a day.

Contact Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com