A while back, we posted about cutting the speed limit as an easy way of increasing fuel efficiency. If speed limits nationwide were reduced to 55 MPH, as they were between 1974 and 1995 under the National Maximum Speed Law (NMSL), American motorists would save billions of dollars each year. Why, then, does it make any sense that Texas is opening a 41 mile, 85 MPH toll road between Austin and Seguin later this year?
The short, no-fun, and empirically-backed answer is, it doesn’t. As we all know, fuel economy peaks at a certain speed—usually somewhere around 50 MPH. After this point, fuel consumption increases exponentially. For example, after 55 MPH, a car rated at 30 MPG would see its efficiency reduced by 8 percent at 65 MPH, 17 percent at 70 MPH, and over 33 percent at 85 MPH. In addition to lower MPGs, drivers on the new road will pay at least $5 in tolls one way. With regular at $3.86 per gallon, this means that a two-way trip in a car rated at 30 MPG would cost drivers a minimum of $10 in tolls and an additional $6 in gas, compared to those traveling on Interstate 35 (which runs parallel and just lowered its speed limit to 55 MPH).
Safety is another concern. The Insurance Institute for Highway Safety has data showing that speed itself, and not just speed variation, increases the likelihood of accidents and fatalities. A 1999 Institute study found that after NMSL was repealed, states that raised their speed limits saw a 15 percent increase in fatalities on interstates and freeways compared to states that did not change speed limits.
Despite these downsides, the tollway offers several benefits. The company that operates the toll road is paying the Lone Star State $100 million to approve the road for 85 MPH rather than 80 MPH–a premium of $33 million. Furthermore, the road will alleviate congestion on I-35, and with the greater speed, save commuters 17 minutes on the 41 mile stretch. It might also get some lead-footed drivers off the interstate.
What it really comes down to is balance. If we only emphasized fuel efficiency and safety, it would be hard to justify traveling above 55 MPH. But, since we also value time, high-speed travel—whether by air, rail, or the road—has a place in modern society. Is 85 MPH too much?
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