To provide maximum traction and stability on all roads, All-Wheel Drive is standard on the Navigator. But it costs extra on the TX.
Both the Navigator and the TX have standard driver and passenger frontal airbags, front side-impact airbags, side-impact head airbags, front and rear seatbelt pretensioners, height adjustable front shoulder belts, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, post-collision automatic braking systems, daytime running lights, lane departure warning systems, blind spot warning systems, rearview cameras, rear cross-path warning and driver alert monitors.
The Lincoln Navigator weighs 529 to 1596 pounds more than the Lexus TX. The NHTSA advises that heavier vehicles are much safer in collisions than their significantly lighter counterparts.

