Modeling and Rendering of a Mercedes S600by Ali Ismail, Jordan Web: www.aliismail.com

Try to add object for your scene for reflections if you had the time and thought the HDRI wasn't enough at one area (or if you are sick like me :) )

I added few lowpoly cars I have from an old project as if they were traveling at the bridge scene to add tiny reflections.

When placing the HDRI I liked the lightning effect given by a particular one for my bridge scene , but the reflections wasn't as much as I wanted, so I made a plane object and given it a new Vray GI material (vraylightmtl), and the texture map for it was another HDRI I liked its reflection, just as the image, I was very careful where to place it so I can get it to reflect on the car body, (you can give it red material for example just to see how its reflecting then give it the texture back)

Unfortunately in max or vray its still not featured to get strong lights to reflect and show rays which would help increase the realism, but for now you can try to add it later in post work.

Although the principle for rendering a car in a scene or as studio render are simple but what makes the difference is each little parameter you need to just keep comparing the renders you have with a real photo with similar conditions to compare and fix what ever you think makes the image look unrealistic.