Driving is dangerous. Duh. Driving while trying to read or reply to a text message is suicidal -- and potentially homicidal as well, so please don't do it.
Of course, modern phones should be able to help out, right? When a new message comes in, why can't you just listen to it the way you listen to voice mail -- and fire off a reply just by dictating?
As it happens, iOS has offered those features for some time, and Android now does as well. Here's how to use hands-free messaging on both platforms.

Android

As you know, saying "OK, Google" to your phone leads the way to all kinds of voice-powered functions. Until recently, however, reading messages wasn't one of them.
Now, however, you can say this: "OK, Google, show me my last messages." You have to phrase it just like that; saying "read my messages" won't work.

Once your phone processes the sentence, it'll display your five most recent texts, announce who the first one is from, then ask if you want to hear it or skip it. If you answer the former, Google Now will read the contents of the message, then give you three options: reply, repeat it or go on to the next one.
And that's it. Assuming you have Google Now configured to work entirely hands-free (meaning you can invoke it without touching your phone), this gives you exactly what you need to listen and reply to messages while keeping both eyes on the road and both hands on the wheel.

iOS

Just like Google Now Lady, Siri can read your latest text messages.
All you do is say, "Hey, Siri" (assuming you've enabled that hands-free feature), then say, "read my text messages." After she reads the first one, she'll ask if you'd like to reply. Say "yes" if you would, or "no, read the next one" if there's another one.
By the way, Siri can also do this for email.
Just like Android users, now you can let your phone do the heavy lifting when it comes to texting and driving.