Access Roads and Traffic Circles
http://www.nj.com/news/index.ssf/2011/08/netcong_traffic_circle_to_be_t.html (not my town but a similar dilemma)
There are just a few small roads that enter/exit my hometown. Two of these roads access the northern part of town, three access the south, and one road each takes care of the east and west. To make matters worse, a vast majority of motorists access town from the south, as a major US highways runs roughly parallel to the town line about 10 miles down past the southern border. For a commercial hub of about 40,000 permanent residents with a nearly doubled daytime population, my town sees significant congestion and excessive travel times during rush hour.
Recognizing this problem, my town’s public works department, in cooperation with the neighboring municipality, has been contemplating the creation of a new four-lane road (two lanes in either direction) that would start at the highway south of town and run northward into our central business district. This road would replace one of the three roads currently entering town from the south and, for many residents and commuters, would promise a chance at relief from the usual congestion. In addition, under this plan, the second road servicing my town’s southern border would become one-way, largely due to the high number of accidents that the narrow road and its many S-curves have seen recently. The third road would remain as is. The thinking behind this plan is that the new multi-lane road would more than compensate for the alteration of the second road.
Braess’ Paradox suggests otherwise, and as someone who is interested in municipal issues, I was shocked to learn in class that the social sciences would disapprove of my town’s attempt at traffic alleviation. Why is this so? Braess’ Paradox says that the appeal of the new, faster road—a “dominant strategy” for any commuter—would lure motorists away from the other two roads, thereby forcing upon one road the traffic that used to be spread out over three. In other words, a great number of travelers would depend solely on the new road, and so significant congestion would occur on said road and travel times would increase. This would be the case even if the second access road weren’t going to become one-way; that part of the plan only serves to augment the possibility of increased travel times.
My town has taken on a few other questionable infrastructure projects in years past. One such project involved replacing a traffic light at a major intersection with a traffic circle. The circle included four access points—one from each cardinal direction—which were controlled by yield signs. The goal here was two-fold: (1) motorists would slow down for the circle more so than for the traffic light, and the circle would be harder to “run” (i.e., disregard, whether intentionally or by accident) than the light, thereby reducing the incidence of serious vehicle accidents, and (2—the real reason for the project) the circle would theoretically reduce congestion at the intersection, eliminating all those lengthy waits at the light (which from personal experience did take an irritatingly long time to cycle through). What ended up happening? While fewer people were injured in vehicle accidents thanks to the slower speeds the circle necessitated, there were more accidents in general (i.e., including accidents without injuries) due to widespread confusion over how to navigate the new traffic pattern. In addition, while the circle certainly alleviated congestion at certain times of the day (such as 3 am), it caused even greater back-ups during rush hour. A few years after its construction, the circle was removed and replaced with a combination of traffic control mechanisms: a traffic light and two off-ramps, one each for northbound travel and southbound travel on the perpendicular road. What this means now is that only motorists continuing east- or westbound on the current road need to use the traffic light, resulting in a far shorter light cycle. This new traffic control system has reduced congestion markedly. That said, there is significant controversy in general among traffic engineers as to which mechanism is more efficient: the circle or the light?