This is called induced demand, whereby something that is plentiful will be utilized since it was built. Commonly, people say "Build it and they will come!" which is all the more true for roads.
Building a freeway or expanding it actually creates more traffic, since it lowers the cost of driving (time & gas) and when building a new freeway you actually create new traffic flows in unexpected ways. Building extra lanes actually causes more cars than those lanes could ever conceivably handle to pour onto the roadway due to the latent demand [1], and the most viable path forward is to create other avenues for said latent demand for transport to be serviced.
Ideally, you will build better mass transit infrastructure, with a sizable light rail network and feeder bus lines in the suburbs. Traffic will not get better due to this in any way, shape or form, but it will lessen the number of additional cars that end up traversing the streets every year, and prevent some additional load.
What this will do though is prevent your local economy from strangling itself in its own traffic, since your community is now providing more than one transport option. The only enemy of transit is density in the US, where we require massive swaths of land be set aside for unused parking that ultimately severely disadvantages every mode of transport, since it forces cities to be more spread out and dense construction to be very costly (underground parking construction costs are insane vs building above ground sqft).
[1] - https://www.wired.com/2014/06/wuwt-traffic-induced-demand/