The seatbelt law can be repealed, IMO, everyone has the right to endanger his own life, as long as it does not endanger anyone else.
Speeding and driving drunk endangers other people.
By the way, most people do not drive too fast and most people do not drive drunk, only a minority does it. I think that if those laws were repealed, the number of people who do that would increase, but not that much.
Speaking of fuel efficiency - if only a tiny minority would choose inefficient cars, there would be no profit in manufacturing them, the companies would not do that (or there may be one company that would cater to that market). In fact, when the fuel efficiency was mandated, but SUVs and light trucks were exempted, more people chose to buy those cars, so, I guess most people really do not care about fuel efficiency that much.
Sure, fuel costs money, but it does not make sense for most people to buy a car that is more expensive and less reliable just to save 1% on fuel costs, because there may be no ROI on that.
In comparison, the government did not need to ban horses, most people chose to buy and drive cars when they became affordable, because they thought cars were better than horses.
The government also did not need to force everyone to get electricity instead of continuing to use candles or kerosene lamps. The government had to force everyone to switch to more efficient lightbulbs.