General Motors is planning to launch a new belt assurance system, which does not allow the vehicle to shift out of park until the driver and front passenger are buckled in, on select vehicles later this year, the company said Monday.

This safety initiative comes in the wake of GM's expanding recall crisis, which today reached 29 recalls covering 13.6 million vehicles in the United States. The company is under multiple internal and external investigations, and it has agreed to a $35 million fine from federal regulators for failing to report safety defects in a timely fashion.

GM spokeswoman Jennifer Ecclestone said the new belt assurance system will be offered as an optional feature in select 2015 models, including the GMC Sierra and the Chevrolet Cruze, Colorado and Silverado. GM does not plan to charge extra for this feature.

Ecclestone said the company would like buyers who opt for the belt assurance system to provide feedback to help improve the technology before it becomes standard.

Last year, ignition interlocks resurfaced for the first time since the early 1970s. These interlocks require seat belts to be fastened before a vehicle can start. Car companies asked the National Highway Traffic Safety Administration to let them use ignition interlocks instead of crash tests for people who don't wear seat belts. NHSTA denied this request in 2013, but said it would study interlocks through 2015 to assess whether they are effective in saving lives.

GM's new belt assurance system does not use an interlock ignition, Ecclestone said. The new system taps into the sensing and diagnostic module used to detect passenger weights and turn airbags on and off. To apply it to seat belts, the SDM detects front seat passengers, and communicates with the brakes and transmission to prevent the driver from shifting the vehicle into gear before both front passengers are buckled up.

The company's OnStar system is included in its efforts to encourage more people to use their seat belts. Drivers who press the OnStar button for non-emergency requests will be reminded to "stay buckled up" during NHSTA's Click it or Ticket campaign, which runs through June 1.

"It is essential for the safety of our customers' and all drivers' safety to develop the habit of buckling up each and every time they get into their vehicles," Jeff Boyer, vice president of GM global vehicle safety said in the statement Monday.

You can reach Nora Naughton at [email protected].