Thanks for your interest with this effect.
It involves several layers in Photoshop. I apply each effect to a background copy, apply the effect in Topaz Studio and then change the opacity to suit and OK it and go back to photoshop and adjust the layer opacity if need be. I then flatten the image (to keep file sizes down) and start on the next effect - make a background copy, go back to TS, choose the next preset and adjust opacity, brightness etc and so on and then press OK, flatten the image again when happy with that step.
'3 truck merge' is a preset from the impression menu with an effect opacity of 0.59 on this occasion. The preset is in the public domain.
Hope that makes sense.