Traffic Forecasting – Past Performance Does Not Guarantee Future Results

Traffic Forecasting - Past Performance Does Not Guarantee Future Results :
Traffic Forecasting – Past Performance Does Not Guarantee Future Results :

Mike on Traffic finds Peak Travel and supports Fix-It-First: Traffic Forecasting – Past Performance Does Not Guarantee Future Results :

“Based on national and local trends, my conclusion is that it is very reasonable to think traffic growth has plateaued. The punchline for traffic impact studies: the “no-build” traffic forecasts should be the same as the existing traffic volumes. We don’t need to do opening day forecasts and 20 year forecasts because they can reasonably be expected to be similar.
And given our huge budget shortfalls, this should also mean a policy of fixing the infrastructure we have. NOT expanding our transportation system to add capacity.”

Linklist: December 13, 2011

There is a Stack Exchange Q&A site proposal for: Transportation (Stack Exchange is a topical Q&A site)

Marginal Revolution: Should speed limits be higher?

Arthur van Benthem, who is on the job market from Stanford, says no:

When choosing his speed, a driver faces a trade-off between private benefits (time savings) and private costs (fuel cost and own damage and injury). Driving faster also has external costs (pollution, adverse health impacts and injury to other drivers). This paper uses large-scale speed limit increases in the western United States in 1987 and 1996 to address three related questions. First, do the social benefits of raising speed limits exceed the social (private plus external) costs? Second, do the private benefits of driving faster as a result of higher speed limits exceed the private costs? Third, could completely eliminating speed limits improve efficiency? I find that a 10 mph speed limit increase on highways leads to a 3-4 mph increase in travel speed, 9-15% more accidents, 34-60% more fatal accidents, and elevated pollutant concentrations of 14-25% (carbon monoxide), 9-16% (nitrogen oxides), 1-11% (ozone) and 9% higher fetal death rates around the affected freeways. I use these estimates to calculate private and external benefits and costs, and find that the social costs of speed limit increases are three to ten times larger than the social benefits. In contrast, many individual drivers would enjoy a net private benefit from driving faster. Privately, a value of a statistical life (VSL) of $6.0 million or less justifies driving faster, but the social planner’s VSL would have to be below $0.9 million to justify higher speed limits. The substantial difference between private and social optimal speed choices provides a strong rationale for having speed limits. Although speed limits are blunt instruments that differ from an ideal Pigovian tax on speed, it is highly unlikely that any hidden administrative costs or unforeseen behavioral adjustments could make eliminating speed limits an efficiency-improving proposition.

[I have not read the thesis, but the key safety gains from raising speed limits come from attracting traffic off the affected roads, see Lave and Elias (1994), who say “We find that the 65 mph limit reduced statewide fatality rates by 3.4% to 5.1%, holding constant the effects of long-term trend, driving exposure, seat belt laws, and economic factors.”]

io9: New map imposes New York City grid system on the world: “If the Manhattan grid system was extended beyond the island, the Prime Minister of the United Kingdom would live at the intersection of 63,709th Street and East 10,894th Avenue. A wild interactive map by Harold Cooper, called ExtendNY, imagines an entire globe laid out according to the New York City grid of the Commissioners’ Plan of 1811.”

BBC News: Every death on every road in Great Britain 1999-2010