Why double piers at expansion joints on viaducts

[roadman65]

Always as a kid my parents used to drive NJ 21 through the double level section at the south end of the freeway. I always remembered the lower level on the NB side where I would watch the piers go by. I always remembered one pier at regular intervals with two piers occasionally.

Now as an adult I know those are the expansion points where the upper level allows for expansion and contraction based on air temperature. However why can one pier on both sides work like on many other bridges?

https://goo.gl/maps/DdViEMoLYX2qqruH7
The above GSV shows what I mean.

[Big John]

On older bridges, it was harder to design bridges as per the moments, so the double pier was a workaround.  There is modern software, so all bridge loads can be determined and the bridges can be designed without the double pier.

[SteveG1988]

Always as a kid my parents used to drive NJ 21 through the double level section at the south end of the freeway. I always remembered the lower level on the NB side where I would watch the piers go by. I always remembered one pier at regular intervals with two piers occasionally.

Now as an adult I know those are the expansion points where the upper level allows for expansion and contraction based on air temperature. However why can one pier on both sides work like on many other bridges?

https://goo.gl/maps/DdViEMoLYX2qqruH7
The above GSV shows what I mean.

I also thought it was there to help spread the load out more evenly across the piers, with the double piers being where loads were heavier