Of course no one ever builds just one sawhorse, you need two, one to support the long end of the board you are cutting, right. When thinking of this it crossed my mind that nowadays when I build something outside or for framing, I use 2 X 6's as much as I use 2 X 4's especially for exterior framing and anything requiring superior strength. To this end, the second sawhorse should be made 2" wider than the above design so both sizes can be cut with the same degree of safety and accuracy and still have the long outboard end supported.
The design below has had the width measurements adjusted to accept 2 X 6's for safe crosscutting. I was too lazy to make a new drawing, ha ha.