How has safety in cars changed over the past 100 years?

Seat belts were added in all Tucker cars as standard equipment in 1948. Since Tucker Corporation only built 51 cars before folding they are not normally known as the first one to do so. In the 1950's Ford (and a few other manufacturers) offered seat belts as an option. 1964 Pontiac made them standard equipment and in 1968 the U.S. Federal government made seat belts mandatory in all new cars sold in the United States.

Laminated windshields came in (I think it was) the late 50's or early 60's. Laminated windshields are 2 pieces of tempered glass, normally .030 thick each, with a sheet of plastic normally .098 thick between them. They are pressed together under very high pressure and heat to make them bond to the plastic. The plastic between the glass helps the glass hold together during breakage so there is not as much flying glass in the passenger compartment. Tempering the glass makes the glass break into much smaller pieces so there are not large fragments flying in the passenger compartment in the event of an accident.

Tempered, laminated glass also assists the airbag in its job by restraining the bag and or passenger, keeping them in the passenger compartment.

Later 70's. They started adding crumple zones(parts of the vehicle were meant to fail to absorb the impact), the old Chevy trucks where one of the first to see these, when the truck was hit hard enough on the front end, the hood was a very solid part of the truck and what happend was the hood would hold its shape and everything else would fail, so the hood would go into the passenger compartment decapitating anyone inside. so if you look at the typical car hood now it has a series of indentions in the substructeur and heave steel hooks that keep it from entering the passenger compartment.

Also in the 70's, Uni-body construction allowed the engine to fall to the ground in the event of a severe front impact so the engine would not end up it the passenger compartment.

80's. They started reinforcing the bodies of cars with door cars and making the unibody a standard almost. The unibody is much different than a frame, a frame when it takes a hit, the force is applied directly to the frame which in turn transfers to the passengers. With the unibody the force of an impact is transfered throughout the entire vehicle which in turn leaves less of an impact for the passengers.

Mid 80's. self retracting shoulder belts were standard and replace the separate lap/shoulder belt. Also the Anti'Lock brakes were developed, and seat belt indicator lights(as norm as it may seem people still need a reminder to click it some times). Some cars had automatic shoulder restraints that would glide into place when closing the door.

70's Airbags were installed in some Ford and Chevrolet models as standard equipment. Both driver and passenger with some models having airbags on the passenger side for the knees also. They were discontinued because of engineering problems and were reintroduced in the late 1980's

Late 90's Curtain airbags, and super tough bodies with built in impact cages(smart car is a great example). Also traction control and stability control.

Future Cars will likely drive themselves and will greatly reduce accidents and the safety features will always get more advanced.