Guardrails are typically installed such that a head on is almost impossible - they are designed for more of a glancing blow that redirects you back to the road. In that application I've seen them keep a fully loaded semi from crossing a medium into oncoming traffic.
To get a head on at speed you would need to going across the road - maybe in the desert it is flat enough to get your car up to speed when going perpendicular to the road, but I'm not sure why you would try that.
The other option is hit the start of the guard rail - while this can happen, the start of guardrails are generally angled so this is still a redirecting blow not head on. Where they cannot be the start is covered by rubber dumpers to slow you down before you hit it.
This is true, but they are also designed with a maximum deflection for a worst case head-on crash.
Typical one-rail guard rails should not deflect more than 2-4ft, while the cable style you see in interstate medians are designed for something like 5-12 ft.
For those comparing this (EVs) to trucks, the difference is center of gravity. Even if a rail is only designed for a given weight, much effort went into containing trucks and other high center of gravity vehicles. The rail catches the vehicle and holds it down, redirecting excess energy into the ground. (Its why cable-styled rails have a gap below the top cable. Others have similar features.)
But what they are not designed for is excess weight with a low center of gravity, where the excess energy just blows through the rail and can't easily be redirected in a more safe direction.
To get a head on at speed you would need to going across the road - maybe in the desert it is flat enough to get your car up to speed when going perpendicular to the road, but I'm not sure why you would try that.
The other option is hit the start of the guard rail - while this can happen, the start of guardrails are generally angled so this is still a redirecting blow not head on. Where they cannot be the start is covered by rubber dumpers to slow you down before you hit it.