USTN is the new traffic provider for all CBS Radio stations nationwide, including WBBM-AM in Chicago. They are not currently using traffic helicopters, but might in the future.
Bart Shore is still working, just not on WBBM-AM. He is under contract to Total Traffic/iHeartMedia. Even if Total Traffic were to release him or he were to quit, he still could not join USTN. There is an agreement in place that prevents USTN from poaching away any full-timers from Total Traffic for an undisclosed period of time. Also, the full-time Total Traffic employees have clauses in their contracts that prevent them from jumping to a direct competitor for a certain period of time. It is quite possible that in the future, Bart Shore and some of the other famous and familiar traffic voices from Total Traffic could once again be heard on WBBM-AM, but it simply is not possible for quite a while.