1) The lake bottom is nothing but silt and mud and goes down thousands of feet. The engineering aspect of a bridge is on order of a major public works projects like the Hoover dam or I-80 over the Rockies
2) Where would a bridge connect? Surface roads of Orem/Provo? The already grid-locked I15? It's not going to alleviate traffic to feed more cars onto already packed roads and highways. You'd just sit on traffic on the bridge.
3) If this dumb idea did come to reality, dont expect EM or SS to see better traffic. Oh no, it would go to crazy town and back with development. That's whats going to happen in Tooele when they build the tunnel to West Jordan.
4) Who would this bridge benefit? jut two or three communities? This is a terrible ROI for the Utah taxpayer. And if you say use federal money you are the problem!
5) The environmental impact on the lake would be disastrous. Treating natural features like trash is how you get trash landscapes. This is why the ski community fought so hard against the gondola between Alta and Snowbird. It takes effort to keep things nice!
6) if you really want better road development, focus on building a urban bypass for I15. I would split at Mona go through Tooele and then build small bridge across the Great Salt Lake to the east side of Antelope Island to connect up in Syracuse back to I15/I84. That relives all N/S traffic and I80 traffic