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InTransition Magazine : Transportation Planning, Practice & Progress

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Research Exchange

Stiffer Road Materials Could Save Fuel

Using stiffer pavements on the nation’s roads could reduce vehicle fuel consumption by as much as 3 percent, according to research by civil engineers at the Massachusetts Institute of Technology.

Asphalt depresses slightly under the weight of vehicles. By modeling the physical forces at work when a rubber tire rolls over pavement, the study’s authors concluded that the point where a road depresses the furthest is just behind the tire—the spot it just finished passing over. This has the effect of making the tires drive continuously up a slight slope, which increases fuel use.

The study’s authors also compared the reaction to a foot walking on beach sand: With each step, the foot tamps down the sand from heel to toe, requiring the pedestrian to expend more energy than when walking on a hard surface. If pavements were even a fraction stiffer, it would decrease deflection and reduce that footprint, according to the study.

The combined effects of road roughness and deflection are responsible for an annual average extra fuel consumption of 7,000 to 9,000 gallons per lane-mile on high-volume roads in the 8.5 million lane-miles making up the U.S. roadway network, according to the authors. Up to 80 percent of that extra fuel consumption could be reduced through improvements in the basic properties of the asphalt, concrete and other materials used to build the roads, according to the study.

The researchers say the initial cost outlay for better pavements would quickly pay for itself not just in fuel efficiency and decreased CO2 emissions, but also in reduced maintenance costs because the roads won’t deteriorate as quickly. This research was conducted as part of the Concrete Sustainability Hub at MIT. More information about the study can be found at

— Researchers: Franz-Josef Ulm and Ph.D. student Mehdi Akbarian, Massachusetts Institute of Technology.

The Diminishing Purchase Power of Gas Tax Revenues

The gas tax is the most significant source of transportation revenue that state lawmakers control, yet most are “built to fail,” according to a report published by the Institute on Taxation and Economic Policy (ITEP) in December.

road construction

The clearest problem with the gas tax structure, according to the report, is that most states operate on a fixed rate, levying a flat fee per gallon of fuel sold. The fixed-rate tax is problematic because its revenue-generating power diminishes with inflation, and can’t keep up with the rapid cost increases on asphalt, concrete, and other transportation construction materials it pays for. After adjusting for growth in construction costs, ITEP reported that the average state’s gas tax rate effectively dropped 20 percent, or 6.8 cents per gallon, since its last increase.

By one measure, states have lost a combined $10 billion due to failure to plan for inevitable increases in the cost of transportation construction. Some states have been experiencing annual losses of over $500 million per year due to gas tax erosion. ITEP recommends short-term gas tax increases, linking the gas tax rate to a long-term measure of transportation construction cost growth, and tax credits to prevent disproportionate impacts on lower income populations.

The full report, entitled “Building a Better Gas Tax: How to Fix One of State Government’s Least Sustainable Revenue Sources,” is available online.

— Researchers: Institute on Taxation and Economic Policy, Washington, D.C.

Foreign Lessons for U.S. High Speed Rail

A recent Lincoln Institute of Land Policy study looked at 50 years of international experience in high speed rail (HSR) to gain insight into applying it domestically. Its principle recommendations include prioritizing rail corridors in a handful of the most viable markets and exploring alternative management and financing arrangements, which include separating development from operations and forging public-private partnerships.

high speed train


The report points to population density and congestion on competing modes of travel as two primary factors conducive to high-speed rail ridership. These factors are present in 11 large “megaregions” that contain 75 percent of America’s population and jobs, according to the report. Furthermore, corridors within these megaregions have comparable length and connect metropolitan regions comparable in size to successful high-speed rail corridors around the world. The Northeast Corridor and California were deemed the most promising markets in the U.S.
While upfront costs are high, the report claims that comprehensive planning for HSR can yield economic development near stations in city centers, as it has with European investments, and improve overall market access.

The study also makes a case that HSR has greater operating energy efficiency and is less land- intensive than competing modes. For example, the report indicates that California would need roughly 3,000 highway lane miles and five new airport runways throughout the state, at twice the cost, to match the capacity of the high-speed rail investments slated for groundbreaking in 2012. Furthermore, a two-track HSR line could transport as many people as a six-lane highway using only one-third of the land, which translates to a savings of 24.3 acres per mile of high-speed rail.

The greater challenges facing HSR for the Northeast Corridor are its fragmented governance among eight states and the District of Columbia as well as the competing rail services that share infrastructure and create congestion.
To read “High Speed Rail: International Lessons for U.S. Policy Makers” in its entirety, visit

— Researchers: Petra Todorovich, Dan Schned and Robert Lane, Regional Plan Association, New York City.

Transportation Workers Overscheduled and Under-Rested

Transportation workers reported sleep-related job performance problems at a higher rate than other workers in a National Sleep Foundation (NSF) 2012 Sleep in America Poll. For the first time, a national poll focused on transportation professionals including pilots, train operators, and truck, bus and taxi drivers about their sleep habits and work performance. Among those surveyed, pilots and train operators were most likely to report safety and job performance issues related to sleep habits.

While sleepiness is common among all workers, 26 percent of train operators and 23 percent of pilots admitted that it has affected their job performance once a week, as compared to 17 percent of non-transportation workers. Furthermore, 20 percent of pilots and 18 percent of train operators reported “near misses” due to sleepiness.

The poll explored questions about scheduling (time between shifts), sleep habits, nap frequency, and caffeinated beverage consumption among these workers as well. Many cited their schedule as a major contributor to sleep problems. According to the study, 44 percent of train operators and 37 percent of pilots reported that their schedule didn’t allow adequate time for sleep, compared to about one-fourth of non-transportation workers and truck drivers and 20 percent of bus, taxi and limo drivers.

Effects are apparent outside of work as well. Pilots and train operators were six times more likely than non-transportation workers to report being involved in a car accident, according to the poll. To read more about the “2012 Sleep in America” poll and other sleep-related research, visit

— Researchers: Thomas J. Balkin and Edward Edens, Walter Reed Army Institute of Research, Silver Spring, Md.; Sanjay R. Patel, Harvard Medical School; Patrick Sherry, University of Denver.

Link Between Daily TV Use, Neighborhood Walkability

Residents living in walkable neighborhoods spend about 15 minutes less per day watching television than residents in less walkable communities, according to research that recently appeared in a health journal.

The researchers gathered data on the sedentary behaviors of 2,199 adults living in low-income and high-income neighborhoods with high and low walkability ratings in the King County/Seattle and Baltimore, Md., regions. In addition to the total time respondents spent sitting each day, the study attempted to measure time spent in seven common seated activities, such as Internet use, reading, talking with friends or listening to music.


The authors acknowledged their surprise that one of their hypotheses was not borne out by the data. There was no major statistical difference recorded in the overall time spent seated by residents of walkable or less walkable neighborhoods. Not surprisingly, a hypothesis that residents of less walkable areas would spend more time per day in cars was supported—about 18 more minutes on average.

The authors concluded that the association shown between low walkability and “two behaviors that have repeatedly been linked with obesity”—watching TV and driving— “adds to a mounting body of evidence justifying a call for transportation investment and land development reforms to increase walkability of neighborhoods.”

The study, “Sedentary Behaviors of Adults in Relation to Neighborhood Walkability and Income,” appeared in the journal Health Psychology in April. For more information, visit

—Justine Kozo and Jacqueline Kerr, University of California, San Diego; Kelli Cain, James F. Sallis and Terry L. Conway, San Diego State University; Brian E. Saelens, Seattle Children’s Hospital, University of Washington; Lawrence D. Frank, University of British Columbia.

Most Teens with High-Functioning Autism Spectrum Disorders Plan to Drive

Sixty-three percent of driving-age teenagers with a high-functioning autism disorder (HFASD) currently drive or plan to drive, according to research by the Children’s Hospital of Philadelphia’s Center for Child Injury Prevention Studies. The study’s authors said it was the first to investigate driving as it relates to teens with a HFASD.

A HFASD is characterized by subtle impairments in social interaction, communication, motor skills and coordination and by a difficulty in regulating emotions. Many of these capabilities can come into play when driving, according to the study.

In a first step to better understand the issue, the researchers surveyed 297 parents of teens with HFASDs and discovered some predictive characteristics among those teens who are likely to become drivers. Compared with eligible but nondriving HFASD teens, the drivers were more likely to be enrolled in full-time regular education, plan to attend college, hold a job or have a parent who taught another teen in the home how to drive, among other common characteristics.

When determining whether a teen with an HFASD is ready to begin driving, the researchers suggested that parents make an appointment with a specialist, such as an occupational therapist or driving instructor, who may be able to offer guidance on how to break driving lessons down into steps that are easier for teens with an HFASD to digest and put into practice. There may also be some legal considerations, depending on the state.

“In Pennsylvania, it’s the law for teens to have a doctor’s sign-off before they can get a learner’s permit and that makes it easier to address driving-specific concerns,” said lead author Patty Huang, M.D., a developmental pediatrician at The Children’s Hospital of Philadelphia. “In states that don’t have those laws, it’s an issue that physicians should be prepared to address with their patients and their parents.”

The study, “Factors Associated with Driving in Teens with Autism Spectrum Disorders,” was published in January in the Journal of Developmental and Behavioral Pediatrics. More information can also be found at

— Patty Huang; Trudy Kao; Allison E. Curry, Dennis Durbin, the Children’s Hospital of Philadelphia.

Study Attempts to Quantify Carsharing’s Environmental Impact

The general consensus of past research has been that carsharing programs bring about reductions in vehicle miles travelled (VMT), private auto ownership and greenhouse gas (GHG) emissions. However, there has been far less agreement about the magnitude of those impacts. A recent study by the Mineta Transportation Institute (MTI) offers a large-scale observation of measurable GHG emissions reductions from carsharing organizations across the continent.



The MTI study evaluates the GHG emissions impact that results from changes in travel when households join a carsharing program. Its conclusions contribute to mounting evidence that carsharing lowers GHG emissions by providing people with automotive access on an as-needed basis.

The study authors observed a dichotomy in the “lifestyle” changes for households that joined carsharing programs. Those who don’t own a car and sign up for carsharing can add to GHG emissions if they switch trips from alternate modes of travel to driving. In contrast, those who give up owning a personal auto and sign up for carsharing generally drive less and decrease GHG emissions.

Overall, the “observed” impact across all respondents was an average emissions reduction of 0.58 tons of GHG per year. The study reported that the total sample of 6,281 households examined shed a total of 1,461 vehicles after joining carsharing programs. The full report, “Greenhouse Gas Emission Impacts of Carsharing in North America,” is available for download at

— Researchers: Elliot W. Martin, Ph.D., University of California, Berkeley; and Susan A. Shaheen, Ph.D., University of California, Davis.

Are Grid Street Patterns Safest for Bike/Ped Travel?

No more than a generation ago, suburban landscapes were frequently designed with cul de sacs and curving streets to increase pedestrian safety by reducing through traffic. A recent study, however, suggests that neighborhoods with higher connectivity—namely compact, grid-like street patterns—are safer for pedestrians and bicyclists.

Past studies have taken a variety of approaches to defining connectivity, the extent to which components of a network are connected. This study team chose four measures—block density, intersection density, street density and mean block length —to explore the association between street patterns and non-motorist safety.

Drawing on data from Alameda County, Calif., the research team evaluated the relationship between connectivity measures and pedestrian-cyclist accidents. It found that denser intersections, denser streets, and shorter block lengths were associated with fewer crashes.

The study deviates from the long-held belief that higher connectivity leads to more car through traffic, which exposes pedestrians and bike riders to more conflicts with motorists and therefore leads to more crashes. Instead, the implication is that the smaller block lengths and more frequent intersections actually reduce traffic speed and force drivers to pay more attention to non-motorist activity.

The 2011 study, “Associations Between Road Network Connectivity and Pedestrian-Bicyclist Accidents” is available in its entirety at

— Researchers: John Bigham and David Ragland, Institute of Transportation Studies, University of California, Berkeley; Yuanyuan Zhang, Zhibin Li and Xiaohong Chen, Tongji University, Shanghai, China.

New Tool Avails Google Transit to Smaller Agencies

Google Transit benefits both transit users and operators by quickly mapping out route and schedule information via computers or mobile devices. However, entering that data into the system can be costly and resource-intensive—often beyond the means of smaller transit agencies.

A 2011 study by Innovations Deserving Exploratory Analysis (IDEA) detailed the development of a tool that aims to make this process available for small transit agencies at a lower cost and with less staff than was previously needed. The Transit Data Feeder (TDF) application developed and tested in this pilot project is available in two formats. First, a hosted configuration in which a transit agency contracts with a host that offers TDF, requires only a personal computer. Second, a local web application allows an agency to load TDF into its local network to host it. TDF is released under an open source software license, making the tool source code accessible and transferable to anyone.

Four small transit agencies participating in the pilot program were provided training and given assistance in preparing their agencies’ transit information (trips, schedules, stops, fares, etc.) for input into the TDF tool and creation of Google Transit System Feed (GTFS) data for Google Transit. These agencies were located in: Park City, Utah; Ignacio, Col.; Savannah, Ga.; and Sumter, S.C.

According to the report, the pilot test results successfully demonstrated that the TDF tool is a viable method for creating the GTFS data streams needed to provide agency transit information to riders and potential riders of a small or medium size transit property. The full report, “Google Transit for Small Transit Agencies,” is available online at

— Researchers: Bruce Williams and Prescott Sherrod, PEMCCO, Inc, Virginia Beach, Va.

Traffic Light Info-sharing Software Cuts Stops, Idling

A joint study by Princeton University and the Massachusetts Institute of Technology found that technologies that coordinate vehicle speed with signal timing have the potential to significantly reduce stop-and-go traffic and save up to 20 percent on fuel consumption.

A goal of Green Light Optimal Speed Advisory (GLOSA) technology is to cut vehicle stops and idling using signal timing information provided by onboard devices such as mobile phones or vehicle computers. The applications are designed to alert drivers headed toward traffic signals in the distance what the optimal speed they should travel is in order to avoid red lights.

The study evaluated SignalGuru, a software that relies solely on mobile phones to detect and predict signal timing. The windshield-mounted phone collects and fuses information on traffic signal length, signal and vehicle locations, and vehicles queued in the intersection to estimate the optimal speed needed to cruise through an intersection without stopping.

Results from two deployments of SignalGuru, using iPhones in cars in Cambridge, Mass., and Singapore, showed that traffic signal schedules could be predicted accurately. In Cambridge, the study found that SignalGuru could predict pre-timed traffic signals within 0.66 seconds. For Singapore’s traffic-adaptive traffic signals, SignalGuru predicted the next color transition with an average error of 2.45 seconds.

In addition to the reported fuel savings, the study found that Signal-Guru helped increase average fuel economy by 24.5 percent in the tested vehicles. The report, “SignalGuru: Leveraging Mobile Phones for Collaborative Traffic Signal Schedule Advisory,” can be viewed in its entirety at

— Researchers: Emmanouil Koukoumidis and Margaret Martonosi, Princeton University; Li-Shiuan Peh, Massachusetts Institute of Technology.

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