And many do. But some automakers only fit equipment to meet the minimum requirement, especially if a model is going to be replaced shortly.
And a carmaker's right to do that--to meet not the "best" safety standard, but simply what's required by law--will be decided this year by the U.S. Supreme Court.
The case involves a 1993 Mazda MPV minivan, which was fitted only with lap belts in the rear. A Federal standard requiring three-point shoulder harnesses in all forward-facing seats didn't take effect until the 2007 model year.
1997 Mazda MPV ES
In a 2002 accident--during which the Mazda MPV hit a Jeep Wrangler that had come loose from the motorhome that was towing it--a rear-seat passenger died.
The victim's family is suing Mazda, arguing that the company should have fitted three-point harnesses even though the lap belt met all Federal requirements.
A California appeals court denied the claim, saying that Federal law preempted state court judgments. The Supreme Court will decide on the family's suit to overturn that ruling.
In general, states may make their own laws, but when they conflict with or exceed Federal requirements, lawsuits like this one frequently occur.
The automakers argue that it would impose huge costs on them to have to meet up to 50 different sets of standards if states were allowed to set their own safety regulations, higher than the Federal rules.
President Obama proved sympathetic to a similar plea in the case of stricter standards set by the California Air Resource Board (CARB) on automotive emissions of greenhouse gases, primarily carbon dioxide.
In that case, a Presidential directive required the EPA, the NHTSA, and CARB to work together to come up with a single set of gas-mileage and emissions standards, released in April.
A similar group recently proposed the first emissions standards for medium and heavy-duty trucks.