United has awarded 36 EMB 145 aircraft to Trans States. It is expected that these aircraft will arrive February of 2015 through 1st quarter 2016. These aircraft fleet numbers have been reflected in the Trans States Pilot Demand projections. For obvious reasons Trans States will see significant hiring this next year, which hiring is likely to start immediately to prepare for the aircraft arriving in Feb. It is likely pilots will be able to plan on a 1 to 2 year upgrade due to this addition which will effectively double the Trans States fleet in a years time.
Since the aircraft being removed from ExpressJet are owned by United, it is possible that these aircraft will be coming from that group of retiring aircraft. For now though where the aircraft are coming from is unknown.