- tra ffic incidents,
- special events,
- holiday tra ffic and
- work zones.
As I see it, the above list doesn't address the root cause -- too many private vehicles, not enough public transit.
Source: Federal Highway Administration
And here's what I see as the biggest roadblock to a sustainable solution.
Source: Driving Alone Dominates 2007-2012 Commuting Trend. (New Geography, 10/9/2013)
As we have seen for decades, more highways and additional lanes and exits only serve to encourage more auto traffic, more driving alone. Until serious efforts are made to change people's long-ingrained driving habits and to provide sufficient funding for public transit, the orange and red lines on the above map are not going to change. In fact, there will likely be a need to increase their width.