I used my own rain file for this low res animation plus a little warping to make it a bit more natural. 
The splashes are actually a population of tiny little white grass clumps. The seed is animated so that each frame has a different seed. "Repopulate every frame" is checked.
I had to cheat a little bit: I used some frame blending in AE to make the appearance of the "splashes" look a bit less chaotic, and there's a bit of tinting the whole scene. 
After I had finished the clip, I realized that each car I picked is blue. I didn't notice that before...
			
			
			
				Ha! Brilliant!
Awesome work Hannes, sorry for the superficial reply, but this is just cool use of TG :)
			
			
			
				Very clever Hannes. Surprisingly great result!
- Oshyan
			
			
			
				Seen a lot of that lately.............frog strangler rain. Great job............... :) 
			
			
			
				
Smart use of Terragen and nice animation Hannes :)
			
			
			
				He looks to be not having a good day. Good stuff on the rain effects.
			
			
			
				Awesome, and really smart, Hannes. Congrats, as some might say  ;)
			
			
			
				Really, really great again, Hannes! And absolutely clever solution with the splashes!  :)
			
			
			
				Thanks a lot, guys! Although it would be great to have a sophisticated particle system in TG, it was great fun to find out how to simulate a particle simulation.
			
			
			
				Yeah, particle system would be too easy. Finding out how to simulate simulations is much more fun  ;D
			
			
			
				 ;D Absolutely cool!
			
			
			
				Indeed! very cool!
			
			
			
				This is great! :)
Matt
			
			
			
				That's so good and surprising it made me laugh...well done Hannes.
			
			
			
				 ;D ;D ;D 8) 8) 8)
Really fun to see that!
			
			
			
				 8) 8) 8)
most excellent dude!
 :)
i want to know what is going on here... my mind is wandering!
:)
			
			
			
				Well Blue is the most popular colour...great trick with the animated grass clumps...will remember that for the future; awesome animation over all..
			
			
			
				Brilliant work Hannes!