Tuesday, May 10, 2005

Policy failures

The Texas Transportation Institute (TTI) garners headlines each year when they publish their "congestion index" and accompanying data. This morning's LA Times cites some of this in "LA Traffic Moving a Bit Faster", although the TTI results are usually bleak and make good news copy.

What do we know?

1. Roads and highways are generally not priced in the U.S. and this policy failure is the real problem. Congestion, as every Econ 1 student knows, is the default rationing mechanism.

2. Suburbanization and the general spreading out of origins and destinations is the safety valve that generally prevents overall "gridlock" -- in spite of the policy failure.

3. TTI typically uses a ratio of available lane-miles vs vehicle miles traveled, usually by county. Yet, for large counties, as origins and destinations move from the core to the periphery, the improvements cannot show up in the TTI index.

4. Survey-based commuting data for the three major national surveys (the decennial census, the NHTS or the American Housing Survey) all tell a different story. They do pick up these relocations and improvements -- explaining the fact that correlations between these (aggregated to counties and metros) and the TTI results are very low.

5. Some of the usual suspects will use the problematic TTI reports because they want to keep on building the usual projects. They will not use them to promote congestion pricing because there is more cash flow in pork projects.

One policy failure begets many others.