Each year, Thailand plays host to several large scale music festivals.
Pattaya seems to be a popular destination for these events, as well as others like the annual Fireworks festival.
One of the issues with these large scale festivals is that if you are not staying there (Like Pattaya), getting to the festival is almost impossible.
100,000 people attend some of these festivals and the roads were just not meant for this much traffic.
Not only that, parking is near impossible.
If there is a must see festival for you, I recommend getting to the location a couple days early and staying in a nearby hotel where you can walk to the festival.
The stress of gridlocked, festival traffic will take all the fun out of it.
If you have to drive to get there, you will have a terrible experience, if you even end up getting that and not stuck in traffic for hours.