It is/was an RX300, and looking at the pics, must have struck the post at a slight angle just in front of the passenger A pillar. The signpost then cutting diagonally across the car, exiting through the off side rear footwell

Not necessarily excessive speed, just no braking... a hefty gust of wind at 70mph will knock a car off course readily enough, let alone an suv or truck... (note the truck stopped on the hard shoulder a little way down the road).
Very lucky indeed... a side effect of platform based cars is that they will literally fall apart if impacted in just the wrong way. Youtube and the like are full of pictures of crashed VW group cars in two or more pieces... they all start with a Polo/Golf floor pan, with extension panels attached in the rear footwell and wider sill panels for the larger cars... catch them hard enough between the front wheel and A post, and the sill/door frames that side simply unzips along the weld, with the floor pan tearing across at either the cross beam just behind the frontseats or where the floor ends at the leading edge of the front seats. What happens to the roof depends on what was hit, but estates/hatchbacks seem to come off alot worse
