I built a full velomobile "fairing" around my recumbent trike with brake lights, turn signals and (not in the picture below) running lights and a great headlight. It tops out around 45mph and will go 50-60 miles on a charge in good weather without pedaling. Some thoughts:
The velo shell keeps me mostly warm, but poking my head out the top at speed when it's below 10F is brutal. Today it was -10F when I woke up, -35 with windchill, so I said "screw it" and drove in to work. 20-32F isn't bad, but the roads are often bad here when it warms up that much; it's usually snowing, everything is slick and visibility is poor. I would not ride in traffic in these conditions, but luckily I work the early shift and the roads are mostly empty.
With a full fairing, my velo very susceptible to cross-winds. I have to keep it below maybe 20mph on days with gusts of 10-20, and it's near unridable on days with more wind.
My trike doesn't have suspension. The roads get torn up in winter, and potholes can ruin your day if you're traveling at 30-45mph, even in a low trike. If it doesn't damage the trike, you might still lose control (especially in slick conditions) and crash. I've wrecked my velo once and while the body protected me, it's not something I want to repeat. I continue to ride but I'm extremely cautious.
I don't want to drive my car any more than I have to, but sometimes it's just not worth it.