[Early_S_Man]

The dual-circuit brake systems came to the USA market for the 1967 models ...

The vast majority now( and for at least the first 10-15 years of all production models) are split front-rear, not dual-diagonal, as pioneered by Volvo or Saab -- I don't remember which! The reliability of the front/rear split dual-circuit brake systems has been so good that most car mfr's don't see the benefit/cost ratio as justifying the extra cost and complexity of dual brake lines to the rear of the car! They would need to equip with dual proportioning valves as well, remember, so those extremely rare situations in which the dual-diagonal design has merit and benefits ... don't justify the effort and cost to equip every vehicle!