Efficient networks take work: Traffic management and Braess’ paradox

Not all roads are created equal. In fact, adding certain roads to a system can actually slow down traffic under the right circumstances. This is a fairly well known phenomenon called Braess’ paradox, named after the German mathematician who first wrote about it in 1968. Fortunately, researchers have studied this occurrence extensively and developed methods for knowing when it can happen and how to prevent it. A new study published in the Journal of Transportation Engineering lays out fairly straightforward methods to identify troublesome links.

When Waze clogs the streets, can communities close them to outsiders?

Reacting to drivers using apps to bypass clogged highways, the borough of Leonia, NJ, has decided to close most of its local roads to non-residents during peak morning and afternoon periods. Many question whether this is a wise or even legal option. In the short run, the shutdown of local roads might make residents happy; but in the longer term, residents could face worsened regional congestion as traffic is forced onto clogged arterials. In dense networks, these local roads can sometimes act like important release valves.

Traffic enforcement observations target Uber and Lyft drivers as largest offenders

A recent scan from San Francisco’s Police Department found that Uber and Lyft drivers were responsible for nearly 65 percent of traffic infractions in bike- and transit-only lanes. The overwhelming majority of these tickets, for all vehicles and for Uber and Lyft vehicles, cited San Francisco Code 7.2.72 TC (see below), “Driving in a Transit Lane,” which comes with a $69 fine. There were also three felony and 29 misdemeanor arrests associated with this traffic report, indicating more serious incidents.

A framework for determining where congestion really matters

These two things are true: 1) Travelers dislike slow traffic, and 2) slow traffic is sometimes an inescapable result of things that people do like—cities with popular destinations. Conventional transportation practice responds well to No. 1, with well-known standards for delay and capacity. Practice has no clear standards to deal with No. 2—what to do in places where speeding up cars amounts to destroying the village in order to save it. A new study of neighborhoods in Los Angeles, a place with more than a little congestion, helps fill this gap.

What HOV requirements in Jakarta can teach us about congestion

According to a new paper from three researchers at Harvard and MIT, removal of a strict High-Occupancy Vehicle policy had negative effects on traffic in Jakarta, Indonesia, the world’s second largest metropolitan area. Congestion increased even on streets with no restrictions and during times when the policy had not been in place. The decision to remove the policy provided an opportunity for a natural experiment in congestion mitigation.

Study of variable speed limits highlights the trade-off of throughput and safety

Varying a posted speed limit based on current conditions can improve operations and safety in congested work zones, a team from Missouri found. This study from the University of Missouri-Columbus explores this phenomenon in a congested work zone in St. Louis, Missouri. The findings? Results depend on whether DOTs are looking to prioritize safety over capacity.

Reducing traffic congestion in cities by delivering goods at night

Shifting store, restaurant, and other business deliveries to nighttime hours could reduce traffic congestion within cities. A study conducted in Stockholm, Sweden, has found that scheduling deliveries to businesses during off-peak (night) times can reduce congestion within a city. Large freight vehicles travelling through urban cores and parking on streets while unloading goods adds to traffic congestion. In addition, traffic congestion cost U.S. trucking companies $63.4 billion in 2015. However, Stockholm is a unique city because it bans truck deliveries between 10 p.m. and 6 a.m., intended to reduce noise in the city during the night.

As federal government mulls performance measures, the TTI congestion report returns

The timing is apparently coincidental, but the Texas Transportation Institute issued its latest estimate of traffic congestion costs in late August, just as US DOT seems to be finishing work on its MAP-21-mandated performance measures on congestion and system performance. Because it is easy to understand, describes a common experience, and is formatted in a series of lists, it is perfectly suited for uncritical press coverage. However, the press attention and catholic policy orientation notwithstanding, the TTI approach is widely criticized on both technical and conceptual grounds.

Virginia adopts multimodal, competitive project scoring process

Last year Virginia enacted legislation to select state-supported transportation projects through a multimodal, competitive process. The law prescribed five areas to be considered in the scoring, along with project cost: congestion mitigation, economic development, accessibility, safety, environmental quality and land use. The relative weights of those elements, and details of how to assess project benefits in those categories, were left to the rulemaking process, which concluded June 17.