Safety is never an absolute. It is not a binary, yes/no variable. It is, rather, a long continuous scale with a whole range of degrees of relative safety.
It is evident from discussions about last week’s Interstate 35W bridge collapse that some people don’t understand this. They want to know whether a bridge is safe or not, period. People try to assure them. On Friday, in her first press conference since the collapse, Lt. Gov. and Transportation Commissioner Carol Molnau heatedly asserted, “If you really believe that any of us would compromise the safety of the driving public, you’re in the wrong place, because we would not.”
Given the situation, it is understandable that the commissioner would try to reassure the public. But her statement reveals a fundamental misunderstanding of safety in engineering.
Engineering design is, at its heart, a series of compromises. Safety may be the most important consideration by far, but engineers also must consider strength, weight, durability, maintainability, adaptability to future changes – and cost. Weighing these usually competing objectives is what we pay engineers to do. Minnesota Department of Transportation engineers generally do it very well, but information is never perfect and people make mistakes.
We don’t want to be killed or injured by our own behavior, but we still make compromises and accept some risks. You forgot the car seat is in the other vehicle and you need groceries for dinner. So you belt your toddler in with an ordinary seat belt to make a 10-block round trip.
While painting on a ladder, you can’t quite reach the edge of those second-story windows. You should re-set the ladder, but the Twins game has already started. Maybe if you just lean out a little further, you will reach it.
The in-laws will be here in an hour. Their bedroom will be a sauna unless you get the air conditioner installed. Grabbing the last extension cord in the house, you notice that it not only is too light gauge for an AC, but the insulation is cracked in several places. You plug it in anyway.
Your brakes have been a little mushy lately. By the time you got home today, the pedal hit the floor. You look under the car and see a brake line is leaking. Getting it towed to your mechanic costs $80. Your credit cards are maxed out. If you re-fill the master cylinder and drive carefully, you can get it there yourself. It is only two miles.
These cases are different, you say. Personal choices are not the same as designing roads and bridges where many lives are at stake.
OK then, think about where you drive. Isn’t there at least one intersection that would be safer with a traffic light? An interchange that would be safer with a full cloverleaf? An on-ramp that should be longer? A rural highway where better sight lines and wider shoulders would reduce passing hazards?
Every state trooper or county sheriff can tell you of particularly deadly locations. Money and better engineering could reduce the perils at most of them.
We all know roads or bridges that could be made safer. But funds are limited and safety is not an absolute. We all live with trade-offs between safety and cost, even if we all don’t agree with the prudence of every case.
The backlog of aging infrastructure, not only in roads and bridges but also in water and sewer systems, is old news. Stories about the problems have appeared regularly for more than a decade. Most of us can see it with our own eyes. Most of us are drivers, most of us pay taxes and many of us vote. We cannot claim to be shocked when there is a bad outcome.
We can piously repeat that transportation officials should not compromise safety even when maintenance budgets erode in real terms. But we know from our own experience that we are more likely to do risky things when we are short of time or money or both. The incentives are the same for highway officials.
The jury is still out on the specific causes of the bridge collapse. It might well have happened even if we had spent more on maintenance over the last decade. But the odds are clear. The less we spend on maintenance and replacement, the greater the overall risk to life, regardless of the details of this specific case.
Commissioner Molnau has been stalwart in supporting her boss’s peculiar position that, even as the economy is strong, we should not spend more money on roads and bridges unless we can somehow pass the bill to our kids and grandkids. Voters tacitly endorsed that position last November. But voters are fickle and the outcome is likely to be different in 2008.
© 2007 Edward Lotterman
Chanarambie Consulting, Inc.