[aidenn0]

The advantages of four wheel steering at driving speeds are largely (completely?) negated by active traction control (supplying power and breaking to each wheel independently). You're not going to see a car turn its wheels 90 degrees because of both the large space needed (the cavity for the wheel to turn in) plus the complexity of linkages that can handle that amount of turning.

This idea might make more sense today than it did back in the day because you can put a small electric hub-motor on the fifth wheel. Downside is that cars are far heavier now than in the 30s so you'd need a beefier lift for the fifth wheel.

[edit]

Looks like Porsche and Renault offer 4-wheel steering in their high-end cars today, which suggest I am wrong about active traction control completely negating the advantages at high speeds.

[TylerE]

The interesting thing with the 4 wheel steering systems is that the behavior actually changed depending on speed.

At low speeds, the rears steered (a small amount) in the opposite direction, for a tighter turning radius.

At higher speeds the steered (again a small amount) in the SAME direction as the fronts, for more stability.

[Nick87633]

The 4-wheel steering on modern cars is typically to help with low speed turning circle size on longer wheelbase cars, not really for high-speed performance although they do put it to use at high speeds for some marginal benefits.

[Tagbert]

The Japanese cars (Mitsubishi and Acura) that had 4-wheel steering only used a very narrow range of deflection to the wheels. It was intended to adjust cornering but not designed for major off-axis motion.

[fomine3]

Toyota Mega Cruiser has 4WS for small turn radius https://global.toyota/en/detail/7882359

[whyenot]

Toyota also offers four wheel steering on the LC500 and of course GM will/does have it as a standard feature on the electric Hummer ('crab walk').