As cities grow and traffic increases, road capacity investments offer diminishing returns and even make traffic worse, according to a recent international study. Looking at 24 cities across the globe, researchers found that for every one-percent increase in road capacity, average traffic speeds drop 0.014 percent. Public transportation doesn’t suffer the same consequences.
capacity
In California speed made crashes more deadly during the pandemic
In California, during the stay-at-home period of COVID-19, people drove less and the total number of crashes went down; but the frequency of fatal crashes increased due to drivers driving faster on open roads. New research leverages pandemic-era speed, volume, and crash data in that state to show that in an urban setting adding lanes to relieve congestion and decrease the number of fender benders can make room for risky behavior and higher speeds that increase the severity of crashes.
Transportation agencies are facing the consequences of induced demand
Induced demand. It’s a concept that used to be popular only among the wonkiest transportation experts, and now gets covered by outlets ranging from the Washington Post to the Wall Street Journal. Governing calls it “the almost universally accepted concept” that almost no one understands, while Strong Towns calls ignorance of the concept “professional malpractice.” With new tools and a better understanding emerging, some transportation agencies are now beginning to wrestle with the implications.
With traffic down, Oregon DOT can move more vehicles at twice the speed
With overall traffic down due to the COVID-19 pandemic, one highway in Oregon is now moving higher traffic volumes at twice the typical speed, according to an analysis by Joe Cortright at City Observatory. This might seem counterintuitive, but it perfectly illustrates the benefits of managing traffic demand, based on simple traffic engineering principles.
Dueling congestion reports released
Two reports issued within days provide contrasting takes on the enduring issue of highway traffic congestion. One report from traffic-data firm Inrix is an update of previous scorecards that rank world cities for highway delay, calculated by aggregating travel times slower than free flow. In contrast, Transportation for America’s new report looks closely at how the frequently-employed solution of highway capacity expansion has worked, and finds it wanting.
New study finds that road closures can alleviate congestion in dense urban areas
Historically, transportation policy addressing vehicle congestion has entailed increasing road capacity. However, research consistently reveals that these policies have the opposite effect. In fact, a new study reveals that cities may be able to improve vehicle travel times by closing certain road segments completely. Using the theoretical framework of the Braess Paradox, the study’s researchers model how blocking off selective streets in downtown Winnipeg can reduce overall vehicle travel times, a change which in turn enables new car-free spaces to be reclaimed as parks or pedestrian plazas.
LA drivers wonder whether expanding the 405 was worth it
After years of construction headaches and a $1.6 billion investment, the Sepulveda Pass project, which expanded Interstate 405, the nation’s busiest highway, appears to have had a minimal impact on congestion. The project, which added carpool lanes, on- and off ramps, and three new earthquake resistant bridges on the 72-mile stretch of I-405 through Los Angeles, took six years to complete and cost $600 million more than the initial $1 billion estimate.
Automated vehicles will bring big highway capacity increases
As the transportation field grapples with the impending impacts of automated vehicles, one AV-related outcome seems clear: Highway capacity will dramatically expand. Because automatic braking systems react much faster than human drivers do, safe spacing on freeways can be reduced by about half. As a result, the current rule of thumb that a freeway lane can handle a flow of 2,000 vehicles per hour will be radically changed.
Automated vehicles will bring big highway capacity increases
As the transportation field grapples with the impending impacts of automated vehicles, one AV-related outcome seems clear: Highway capacity will dramatically expand. Because automatic braking systems react much faster than human drivers do, safe spacing on freeways can be reduced by about half. As a result, the current rule of thumb that a freeway lane can handle a flow of 2,000 vehicles per hour will be radically changed.
New Jersey DOT: no more roadway expansions
New Jersey’s newly appointed Department of Transportation Commissioner announced the agency will pursue a ‘fix-it-first’ mindset toward transportation spending. “The days of system expansion in New Jersey are long over, we don’t have the funds,” he said. “The focus is on the new status quo, paving, repairing deficient bridges, fixing potholes.”