Toll roads 36% safer than tax roads - IBTTA study

Tollroads are 36% safer than free roads according to data published by Jeff Campbell in an article "Toll vs Nontoll: Toll facilities are safer" which will appear in the next issue of the IBTTA journal TOLLWAYS. Campbell is the research manager at IBTTA. The 35% is our estimate based on a fatality rate of 8.1 per billion vehicle miles traveled on all the nation's expressways which we get from FHWA's Highway Statistics 2006 publication and on Campbell's survey result of 5.2 fatalities per billion miles traveled.

Campbell got data from 39 tollroads, 30 toll bridges and 6 toll tunnels in 20 states. Fatality rates were even lower per billion miles traveled on bridges (2.7) and tunnels (1.4) so that for all toll facilities the death rate was 5.0/bVMT.

Campbell in his report compares toll facilities' fatality rates with urban interstates which he says have a fatality rate of 5.5/bVMT and with rural interstates 12.1/bVMT. Our numbers from FHWA are marginally higher.

Since tollroads are a mix of urban and rural it seems to us the better comparison is with the nation's mix of urban and rural interstates plus the non-interstate urban expressways - that is with all expressways. The last category of non-interstate freeways/expressways contain some of the older expressways built before interstate grants and they tend to be of the same vintage as older tollroads.

Using the all expressways 8.1 fatalities/bVMT as the denominator the Campbell estimate for tollroads facilities of 5.2 gives 64% as the safety factor for being on a  tollroad as opposed to a tax road of the same general expressway class.

Toll bridges and tunnels don't really have any large counterpart sample on the tax side since there are very few untolled major bridges and tunnels, so we think they are better left out of the comparison.

All roads in the US had 43,896 fatalities for 3,009bVMT or a rate of 14.6/bVMT but since that includes a huge mileage of more dangerous undivided road with surface intersections and uncontrolled access it seems to us invalid to use in comparisons.

We've previously published the numbers for a few tollroads that published their fatalities and VMT data and they suggested that tollroads were clearly safer, but we couldn't say by how much. The sample was too small and probably unrepresentative.

Campbell's estimate is a valuable piece of work because it is the first time the fatality rate on tollroads has been systematically estimated.

The 11 page study is available here: http://www.ibtta.org/files/PDFs/win08_Campbell.pdf

FHWA data is in downloads here: http://www.fhwa.dot.gov/policy/ohim/hs05/roadway_extent.htm

TERMINOLOGY: Campbell sticks with the more common safety measure of fatalities per hundred million vehicle miles traveled, so his numbers are a tenth of ours. The 100 million demoninator is a clumsy anachronism that goes back to the time when death rates were ten or twenty times what they are now and the smaller denominator was needed to gain a single digit result like 8 deaths/100m vehicle miles traveled. A hundred million is a nonsense denominator - there are thousands, millions, billions, trillions. In any case safety has improved so much that most of the results expressed the old way are now decimals.

TOLLROADSnews 2008-03-18