Statistically, distracted driving is one of the biggest risk factors on the road. In the past two years or so, traffic accidents have seen a significant rise, and many think that modern smartphones are at least partially, if not mostly, to blame. It doesn't take much these days to get drivers to take their eyes off of the road; a stray text message or even a wandering Pokemon is all it takes in some cases. The National Highway Traffic Safety Administration, among other US regulators, are calling for smartphone manufacturers to step in and do their part to buck this disturbing new trend.
Regulators are asking manufacturers of smartphone hardware and software to find a way to implement a safer mode of operation for driving, with features stripped out and only those that should be used for driving, such as navigation and music, left accessible. Such a mode would likely mirror the "driving mode" apps that can be found all over the Play Store right now, except that the driver would not have a choice in the matter; when the vehicle is in motion, they will be forced into using the mode. The kicker, of course, is that manufacturers have to figure out some way, besides making the driving mode voluntary, to place this restriction only on the driver of a vehicle, allowing passengers full use of their devices. There are any number of possible ways that such a system could be implemented, but they all have their flaws; it would be up to manufacturers to figure out the best way for their hardware.
Unlike drivers who would be making use of the driving mode that the NHTSA is asking for, manufacturers are not being forced to make this move. The NHTSA does not technically have the authority to force smartphone makers to implement a driving mode like what they're asking for, so regulators are hoping that they'll simply play ball without any arm-twisting. In the past, the NHTSA made a similar move in regards to in-car infotainment system rules, and companies that manufacture them adopted the suggested standards. There's no telling whether smartphone makers will actually do the same, but with petitions and suggested laws concerning distracted driving popping up all over the place, skipping out on such a move would likely garner the ire of some consumers.