Almost all freight from Mexico to the US and vice versa gets offloaded at a warehouse on the border and then switched to a different driver/mode of transportation as having a driver eligible to do the whole trip is hard to come by and expensive.
That being said, the rail ramp in Laredo, TX (the crossing point of Nuevo Leon, MX and the US) is active and widely used. Issue is that rail is slow so if your shipment has any urgency, you just use a truck. I use both and while US rail companies suck to work with, they can be very effective cost wise and help keep our total carbon emissions down. But nothing beats a truck in terms of speed and availability in the US…
When I found out my cousin in Turkey who worked at a major car manufacturer as an engineer made less with a PHD then I did waiting tables in the US is when I realized how messed up it was for young people in Turkey.
He has since moved to Belgium and gets paid quite well.