I've been in the same situation for about five years, but haven't the budget to buy a new car with driver assist features -- it was all I could do to buy one with high enough fuel economy not to break me at the gas pump.
There is no lifehack to replace getting adequate sleep. There are a few basic things you can do to help ensure that you're rested each morning (which will, in turn, contribute to avoiding issues with alertness when you drive home).
First, either completely avoid caffeine, or else cut yourself off at least five hours before you expect to need to sleep (six or seven hours is better). This will both make it easier to fall asleep at night, and improve the quality of your sleep, so you'll be more rested after the same number of hours asleep.
Second, avoid "screen time" for at least an hour before bedtime. That includes TV, computer, tablets, phones, even digital camera viewscreens. If you can't avoid screen time (really?), there are applications for most operating systems that will filter the screen color to reduce the blue light that tells your brain it's time to be awake, but avoiding the screen also lets your mind relax, letting go of the stresses that go with using the computer or phone, or the stimulus that TV brings.
Third, ensure you have at least seven hours uninterrupted to sleep. Nearly every adult requires between seven and nine hours of actual sleep (not counting time in bed reading before sleep, etc.).
Fourth, avoid sleep aids of any kind. Even alcohol, though it may make it easier to fall asleep, degrades the quality of sleep by disrupting dream cycles and increasing the tendency to wake through the night. Most other sleep aids have similar, but greater effects: you'll sleep, but you won't rest as effectively.
If all of this still doesn't let you remain awake and alert for fifteen or sixteen consecutive hours, see if you can't work in a snort nap after lunch. This is a common social practice in a number of countries, though it's fallen out of favor in America.
If you're still having trouble staying awake for your drive home, see your doctor. There are a number of sleep disorders that you might have without knowing, ranging from the commonest (sleep apnea) to some really off the wall ones that, honestly, your doctor and a sleep specialist may still discount. Sleep apnea, however, is so common that modern medicine tends to assume everyone has it to some degree. There are non-drug treatments (usually involving either oral appliances to prevent airway collapse or a pressure breathing mask called CPAP) that will alleviate sleep apnea well enough to make a world of difference in sleep quality.