Recently, I wasted about an hour late one night on detours and traffic jams because a three-mile stretch of Interstate 5 is shut down for widening every night from 11pm to 4am. It illustrates a lot of the unpleasant tradeoffs on the horizon in Obama's Daleyesque ideas for "infrastructure stimulus" spending.
This is the main West Coast highway from San Diego to Seattle, so it's a crucial artery for trucks, but the long stretch just south of downtown LA, the old Golden State Freeway, is only three lanes each way. For some number of years now, CALTRANS has been adding a fourth lane each way for a stretch at the southern end of the bottleneck in northern Orange County. I have no idea if this will do much good for northbound drivers heading to downtown LA since they still must squeeze down to 3 lanes eventually. For southbound drivers, it will mean traffic speeds up three miles earlier as they go from 3 to 4 lanes.
Notice, however, that because I-5 is such an important part of the nation's infrastructure, it is only being shut down 5 hours per day: 11pm to 4am. That's barely half a shift -- not much of a job creator and not much of a quick stimulus either. Or Obama could pay to run two shifts a day, creating lots more construction jobs ... and completely snarl Southern California traffic.
I suspect a lot of similar tradeoffs will emerge in transportation stimulus spending.
One thing that was readily apparent that night was that there's a fairly low maximum tolerable density for simultaneous infrastructure projects, which limits how fast you can spend money on infrastructure stimulus. Shutting I-5 was tolerable to me because I-91, which I used for a long detour because it crosses I-5 at a 45 degree angle, wasn't also shut for upgrading. If they'd both been closed for work, I'd still be out there.
That means that the optimal pace of spending on infrastructure is slow. SoCal freeways, for instance, can aborb a lot of taxpayer money, but they can't absorb them all that fast without making traffic much worse than it is now.