The arrival of autonomous vehicles has prompted many to imagine a world without annoying traffic signals. If cars are smart enough to drive themselves, one is inclined to reason, why cannot they simply chart a crash-free path through at-grade intersections all by themselves? In this paper, we ask: is eliminating signals from intersection desirable, even if it is possible? The abstract below provides a short answer (hint: Yes and No). If you are interested in reading the full paper, a preprint may be found here. The paper recently appeared in Transportation Research Part B.
Abstract: We model and analyze a futuristic intersection that serves only connected, autonomous and centrally managed vehicles. Under consideration are three control strategies that aim to minimize the total system delay by choosing an optimal trajectory for each vehicle. The first two abandon the concept of signal timing all together whereas the third strategy keeps it. The difference between the two signal-free strategies has to do with a fail-safe buffer requirement introduced to provide redundancy. Each control strategy leads to a unique version of a trajectory-based autonomous intersection management (T-AIM) problem, which is formulated as a mixed integer linear program and solved using a variety of techniques. We found the signal-free strategy holds an overwhelming advantage over the signal-based strategy in terms of efficiency. However, its success is fragile and dependent on the faith in the safety and reliability of the system. When the fail-safe buffer is introduced, the efficiency of the signal-free strategy degrades to a level comparable to that of a properly designed signal-based strategy. Surprisingly, the signal-free strategy with redundancy tends to arrange vehicles in groups that take turns to cross the intersection together. This “signal-like behavior” manifests itself whenever congestion rises to certain threshold. In addition, solving the T-AIM problem based on signal timing enjoys significant computational benefits, because it eliminates cross conflicts. Thus, the basic logic of signal timing—if not the physical equipment—may survive even after humans are no longer allowed to drive.
Fred Hirsch was no big-time economist. His brief academic career was cut short by ALS, the same disease that killed Tony Judt. Yet, his Social Limits on Growth is a masterpiece, probably not a book you could read for fun lying on the coach, but definitely worth the time and effort.
Winners take all is about the dream of “doing well by doing good”, the idea that there is always a win-win solution to every social problem, and the belief that elites equipped with technology and market tools should be entrusted to lead social changes, preferably independent of the democratic processes, or politics. The author argues these ideas are largely an illusion, if not a deception, because the overlap between individual and collective interest is limited. There is nothing wrong about wanting to do well by doing good; but we are kidding ourselves if we believe these do-gooders are saviors of our collective future. The book is very harsh on the intellectuals who promote these ideas. These so-called “thought leaders” are described as the cheerleaders employed by the “idea industry” to project positive energy, presumably at the expense of our collective good.
Overall, Antifragile is a disappointment. This is not to say it offers no interesting and useful ideas. It does. What strikes me the most are the oversized impact of tail events (black swans) and their utter unpredictability, our ruinous obsession with optimization and intervention, and the agent problem ubiquitous in modern societies. However, Taleb could have explained these ideas in 40 pages. Instead, he wrote 400, filling many of them with impulsive bragging, as well as his signature rant against the entire intellectual establishment. In the end, I felt these self-inflicted distractions severely undermine the narrative and the logic flow. I was looking forward to reading Black Swan, but after this experience, I wonder whether it would be worth my time.