Читать книгу Confessions of a Recovering Engineer - Charles L. Marohn Jr. - Страница 10

When an engineer sits down to design a street, they begin the process with the design speed. I have been in countless meetings where engineers presented technical design sheets and even in-depth studies for a street project. Never, and I mean never, was any elected official or any member of the public asked to weigh in on the design speed.

Never once did I hear one of my fellow professional engineers say, “So, what are you trying to accomplish with this street in terms of speed?”

No. The design speed is solely the purview of the engineering professional, with a preference for accommodating higher speeds over lower.

Why?

Choosing a design speed is, by its nature, an application of core values. When we pick a speed, we are selecting among different, competing priorities. Is it more important that peak traffic move quickly, or is it more important to maximize the development potential of the street? Do we compromise the safety of people crossing on foot in order to obtain a higher automobile speed, or do we reduce automobile speed in order to improve safety for people outside of a vehicle?

These are policy decisions, and like all policy decisions, they should be decided by some duly elected or appointed collection of public officials. In a democratic system of representative government, representatives of the people should be provided the full range of options and be allowed to weigh them against each other. That rarely happens, and I have never heard of an instance where it has happened for a local street.

Many of my engineering colleagues will reply that they do not control the speed at which people drive — that travel speed is ultimately an enforcement issue. Such an assertion should be professional malpractice. It selectively denies both what engineers know and how they act on that knowledge.

For example, professional engineers understand how to design for high speeds. When building a high-speed roadway, the engineer will design wider lanes, more sweeping curves, wider recovery areas, and broader clear zones than they will on lower-speed roadways. There is a clear design objective — high speed — and a professional understanding of how to achieve it safely.

There is rarely any acknowledgment of the opposite capability, however: that slow traffic speeds can be obtained by narrowing lanes, creating tighter curves, and reducing or eliminating clear zones. High speeds are a design issue, but low speeds are an enforcement issue. That is incoherent, but it is consistent with an underlying set of values that prefer higher speeds.

Once the engineer has chosen a design speed, they then determine the volume of traffic they will accommodate. How many motor vehicles will this street be designed to handle? This is the second step of the design process, and the second instance where the design professional independently makes a decision that is, at its heart, a value decision.

Standard practice is to design the street to handle all of the traffic that routinely uses it at present, plus any increase in traffic that is anticipated in the future. There is no consideration given as to whether that is too much traffic for the street, and rarely is there a conversation of whether other alternatives should be considered. If traffic is present, it is the traffic engineer's calling to accommodate it. No nonprofessional is given an opportunity to suggest otherwise.

Now that they have identified the design speed and traffic volume, the traffic engineer consults one of the books of standards to determine how to assemble a safe street. Given a certain speed and volume, how does the design cookbook indicate the street's ingredients be assembled? Within the design process, the answer to that question is, by definition, safe. Any other design would generally be considered a compromise of safety.

The final step of the design process then is to take the “safe” design and determine how much it will cost. This dollar amount is the price for a responsible street design. Any questioning of this minimum effort would be considered a reckless endangerment of human life.

Now we have the traffic engineering profession's values as expressed in the design process. In order of importance, those values are traffic speed, traffic volume, safety, and cost.

I have presented the profession's values in this way to dozens of audiences, comprising thousands of people, across North America. I then ask them to identify their values. These are mixed audiences of professionals and nonprofessionals, people involved in local government decisions and those who are not. There is always a broad consensus (Table 1.1).

I ask them to think about a street where they live, or one where they shop or like to go out to eat. I then ask them to shout out, in unison, which value they consider most important as applied to that street. The answer, overwhelmingly, is safety.

And of course, it is. Most humans, including most traffic engineers when they stop to consider what is being asked, would sacrifice much of the street's performance in terms of speed or volume in order to make it safer. Safety is the top value nearly all people apply to street design.

As we continue, I ask for them to shout out their second most important value. Again, there is no real ambiguity. Nearly everyone chooses “cost.”

Again, most Americans today would sacrifice the ability of someone to drive at speed, and the capacity of a street to accommodate a specific volume of traffic, to have a more cost-effective design. I acknowledge that this collective response may differ from the preferences of the individual driving the street,¹ but there are always competing interests between an individual and society. In public policy, we routinely ponder such tradeoffs.

While safety and cost are the top values for nearly everyone, the third value expressed by the groups with whom I have interacted is perhaps the most telling. I ask, “In a tradeoff between speed and volume, would you prefer a design that moves fewer vehicles at a higher speed, or one that moves more vehicles but at reduced speed? Would you emphasize speed or volume?” The answer, overwhelmingly, is “volume.”

Table 1.1 Values Applied to the Design of Streets*

Current Practice	Most Humans
Design Speed	Safety
Traffic Volume	Cost
Safety	Traffic Volume
Cost	Design Speed

^* In order of priority, highest priority first.

And that makes sense. To the extent that the street is used to convey traffic,² sacrificing the number of cars that can pass through in a given time frame just so those drivers can go faster is counterproductive by any meaningful measure. If we can slow down traffic speeds, and it means that more vehicles can pass through and people arrive at their destinations sooner, why would we not do that? Most people would.

The values of the design process — the values applied to street design —are not values that most people would identify with. I would assert that this includes most traffic engineers, which suggests that design professionals are not morally deficient people but simply that they have accepted these underlying values without debate, internal or otherwise.

State Street was designed using a process that values speed and volume above safety. Sagrario Gonzalez was expected to overcome this design. A different set of values, a more human set of values, would not have put that burden on her.