According to the Regional Transportation Council 2030 Mobility Plan, the eventual demand for this portion of LBJ is 500,000 vehicles per day by 2020. There is no way the facility can be built to handle this demand. Even upon completion, the roadway would be outdated.
However, in order to account for this massive increase in capacity, traffic must be managed by developing programs controlling the speeds of drivers through the corridor. Thus the reason it is necessary to have TEXpress Lanes to keep traffic moving through the corridor.