A loud blaring horn is more likely to have the opposite of the desired affect, startling the driver and causing him/her to let off the throttle and hit the brake rather than to speed up. Making the situation even worse.
Better idea. Accept the fact that everyone drives differently, look far ahead and anticipate the slower drivers, let them go their way, and then go yours. Much better for your (and their) peace of mind, reduced stress, and overall happiness. Relax, slow down, and enjoy life to the fullest while you can for you too will be an old geezer before you know it.
Don't sweat the small stuff. And that definitely is small stuff.
