Presentation on theme: "Fourth Annual Preserving the American Dream Conference Atlanta September 16, 2006 Reforming Public Transit – Transit and Congestion Relief Thomas A. Rubin."— Presentation transcript:
Fourth Annual Preserving the American Dream Conference Atlanta September 16, 2006 Reforming Public Transit – Transit and Congestion Relief Thomas A. Rubin
Reason Foundation Galvin Mobility Project A series of professional papers on mobility First ones have been published, available at: http://www.reason.org/transportation/ Many more now in works I’m doing one on the relationship between transit and traffic congestion
Process Test hypothesis: Transit has a Significant Positive Impact on Traffic Congestion (as transit usage goes up, congestion decreases) Study Population is U.S. Urbanized Areas Transit Usage data from National Transit Database (NTDB) (independent variable) Traffic Congestion data from Texas Transportation Institute (dependent variable)
Transit Usage Data NTDB data from Florida Transit Information System (FTIS) Allows single inquiries for multiple data items for multiple years Data elements selected: –UZA Total Unlinked Passenger Trips –UZA Total Passenger-Miles –UZA Total Light Rail Unlinked Passenger Trips –UZA Total Light Rail Passenger Miles
Traffic Congestion Data Texas Transportation Institute (Texas A&M), Transportation “Travel Time Index” (TTI) (Schrank and Lomax) TTI is ratio of time required to travel at peak hours:time required to travel with free-flow conditions
Data Data available from both sources for years, 1984 to 2003, inclusive – 20 sets of data for each UZA TTI UZA’s – 69 Total: –13 Very Large (3,000,000 < population) –26 Large (1,000,000 < population < 3,000,000) –30 Medium (500,000 < population < 1,000,000)
Data Quality/Quantity Both NTDB and TTI are generally good, not perfect In general, quality of data improves as present day is approached 69 UZA’s with 20 years of data each; 1,380 sets of data
Process: Run various simple and multiple regressions to test alternative relationships Test for each UZA individually and for entire population of 69 UZA’s To do test for all 69 UZA’s, data had to be “normed”
Issues with TTI See Cox & O’Toole, The Contribution of Highways and Transit to Congestion Relief: A Realistic View, Heritage Foundation, Backgrounder #1721, January 27,2007: http:// www.heritage.org/Research/UrbanIssues/bg1721.cfm Relatively low correlation with actual Travel Time (ACS)
Interim Report I had my associate do the analysis for two UZA’s to test the data Figured, what-the-heck, do the regressions and see what we get Overall expection? Not much connection – congestion is basically a supply-and-demand thing and transit is just a small percentage of total transportation in most UZA’s. So, here’s the results – for Portland, Oregon
Well, Why Not? Rule 1: “Correlation is not causation.” 20 data points for one UZA is just a bit thin for drawing this type of conclusion. Most important, what possible direct causation could there be between, all else equal, an increase in transit usage – presumably, taking vehicles off the streets – and congestion getting worse?
But, All Else Isn’t Equal in Portland First Portland Light Rail Line was largely funded with Federal “Interstate Transfer” funds – Portland (or, more properly, the Mayor of Portland, with assistance from other officials) decided to give up an urban Interstate that had already been approved and funded to build this line. An urban freeway has several times the “transportation work” capacity than any light rail
But, All Else Isn’t Equal in Portland II Building this light rail line required taking out a pre-existing HOV lane from a freeway that had higher transportation work values than the light rail line Building light rail on surface streets has reduced road capacity on these arterials and made crossing movements more difficult
But, All Else Isn’t Equal in Portland III Portland (Metro, Tri-Met, State, et al) have largely decided to not implement road capacity improvements – as demand increases Portland et al have adopted LOS “F” as the official target – while this is the result in many UZA’s, at least the others are officially trying to do better, not worse
So, can transit actually cause congestion to increase? No, not by itself. But, as a component of an officially adopted program of “interesting” transportation decisions, a case can be made.