Per the answers here we know that four-wheel steering is a mainstream (even if uncommon) feature in commercial autos. Generally it appears that at high speeds and for small turning rates it will turn the rear wheels in the same direction as the front wheels, causing the car to "snake" or "crab" sideways without introducing a yaw moment. (I can't find a canonical term for this type of steering. So I'll stick with "snake" for now.)
It suspect that snaking is preferable to turning for emergency lane-change maneuvers for two reasons:
- It is less demanding of traction: It loads the outside two wheels equally and doesn't introduce a yaw moment. In contrast, a turning lane-change first loads the front outside, then the rear outside, and then does the same sequence on the other side as it tries to straighten out in its new lane. As speed increases this is the perfect recipe for inducing a spin (or, with a high center of gravity, a rollover) when one approaches the limit of traction. I would expect that a vehicle can execute an emergency lane-change by snaking at significantly higher speeds and rates than it can by turning.
- I think a snaking lane-change can be performed in a shorter distance, because both outside tires are loaded simultaneously, and the translational moment is always less than that translation plus a rotational moment.
Are either or both of these suspicions correct? And if so, can anyone provide numbers to indicate how much faster and/or shorter snaking can maneuver than turning?
(Note that, if correct, these features mean that a car that can execute a snaking lane-change would be able to avoid obstacles that it could not in the same situation using a turning lane-change.)