A runaway is like being in a vehicle that's out of control. If the vehicle is going 100 mph and you turn the wheel sharply, you'll likely roll it. However, if you turn the wheel a little bit, that will slow it down a bit. Then turn it a different direction and that will slow it down a little bit more.
Pretty much by definition, something unexpected happened to make a horse a runaway, so you have to look for the best scenario in a bad situation. You might have to actively remind yourself to keep your head and remember that the faster your ground speed becomes, the more slowly you must make your own actions. You pick up the rein little by little and bring your horse down to a stop little by little. Don't just rip his head around.
You can use the hindquarters of the horse to gradually bring him to a stop. Pulling on both reins is not as effective as pulling on one, but you might have to alternate sides to be effective.
If you pick up on the right rein, start a slow pull, and that horse just keeps going, he has probably braced his neck. It's really hard for a rider to do, but you have to let go of that right rein and pick up on the left rein. Pull. Hold it for 3 seconds. Release. Go back to the other side. Pull. Hold. Release.
If you get the horse to change directions, he will slow down and eventually stop. Turn the horse to the right for half a circle (or as much of a circle as you have room for) and then turn the horse to the left for another half circle and then turn the horse to the right and then turn the horse to the left.
When you get home, realize that the mistake that caused your horse to bolt was made two or three days earlier. The problem in the training was created before the day your horse ran away, not the day that he ran away. It wasn't created by the object or the situation that scared him. It was created by what training was not done the day before with the horse, or the last time the horse was ridden. When that situation happens, don't blame your horse, don't look at the situation or look at that day. Look at what you didn't do the prior days to get this horse ready for it.
Don't work on problems with horses. Focus strictly on what it is you want the horse to do, the cues you want the horse to respond to. Get the horse better always at responding to your cues. Don't work on don'ts. Work only on do's to get the horse to do what you want.
Then go have fun together.