Interstate truck and bus drivers are prohibited from using handheld cell phones while driving as of today, Jan. 3, under a final rule posted by the Federal Motor Carrier Safety Administration and the Pipeline and Hazardous Materials Safety Administration.

Drivers will face federal civil penalties of up to $2,750 for each offense and disqualification for multiple offenses. States may suspend a driver's commercial license for multiple convictions of state or local cell phone violations.

In addition, companies that allow their drivers to use hand-held cell phones while driving will face a maximum penalty of $11,000.

Some 4 million commercial drivers are affected by this final rule, according to the agencies.

FMCSA said research shows that using a handheld cell phone while driving requires a commercial driver to take several risky steps beyond what is required for using a hands-free phone, such as reaching for the phone. Drivers reaching for an object are three times more likely to be involved in a safety-critical event, the data shows. And dialing a cell phone increases the risk to six times.

The agency said it will work with the enforcement community to develop procedures to ensure uniform application of the rule. "Enforcement programs can be successful," the agency said. "Since our texting rule was implemented (last year), FMCSA has had over 300 violations at roadside."