"It requires sensors that see a long dis- tance and very high- performance computers, which are very expensive," said Ken Koibuchi, Toyota's executive general manager for autonomous driving.
But another reason is Toyota sees wider safety benefits from prioritizing the proliferation of more basic technologies such as lane-trace assist and systems that prevent pedal misapplication.
The more advanced Lexus technologies, such as automatic lane-change, are also arriving late in the U.S. — after being offered in Japan.
The reason, again, is safety. In the U.S., it takes longer to verify the systems for the diverse driving conditions, patchwork of traffic laws, faster speeds and divergent driving habits.
"Many U.S. roads have blurred lane markers or a variety of different lines drawn on the road. It's very difficult," Koibuchi said. "We have not done sufficient verification yet."
Toyota Motor has traditionally developed such self-driving technology in Japan and then tried to tweak it for U.S. driving conditions. But increasingly, the company will develop the technology for both markets in parallel, Koibuchi said.
The just-redesigned Lexus LS flagship sedan, for example, gets several self-driving functions in Japan that won't be initially available in the U.S.
One is lane-change assist. Another is a lane tracing feature that automatically steers the car through highway bends.
It does so by automatically slowing the car when a curve is coming so that the LS can keep automatically tracking the lane.
That function relies on highly detailed GPS mapping, which is widely available in Japan.