Articles

Celebrating Independence Day!

Where baby freeways come from

Tomorrow is Independence Day here in the United States, whi means the library (and the whole UC Berkeley campus) will be closed in observance of the Federal holiday. 

It also means holiday traffic as people head out of town for a long weekend, outdoor recreation, or to fireworks displays.  Holiday weekends tend to see an over-representation of fatal and injury crashes on the roadways, largely due increased drunk driving. Increased impaired-driving enforcement has helped reduce crash fatalities in the United States. Checkpoints could be even more effective with location optimization modeling

So have a festive and safe weekend. Don't drive impared. We'll see you next week!

Examining Electric Vehicle Parking

Electric Vehicle Parking

Electric vehicle (EV) public parking has been rolling out in Berkeley but got a boost recently with station installed at both Whole Foods. The city is slated to get more municipal charging stations soon, including a pilot to look at curbside charging stations

There are mixed opinions about EV public parking options, with concerns about location and demand. Researchers are looking at activity models to overcome public perception and be more effective in urban areas. A new article from Transportation Research Part A: Policy and Practice continues the discourse. "Electric vehicle parking in European and American context: Economic, energy and environmental analysis," by Marta V. Faria, Patrícia C. Baptista, and Tiago L. Farias, applies a methodology for the placement of EV parking to Lisbon, Madrid, Minneapolis and Manhattan. They conclude:

This research confirms that the success of deploying an EV charging stations infrastructure will be highly dependent on the price the user will have to pay, on the cost of the infrastructure deployed and on the adhesion of the EV users to this kind of infrastructure. These variables are not independent and, consequently, the coordination of public policies and private interest must be promoted in order to reach an optimal solution that does not result in prohibitive costs for the users.

The full article can be read here.  

 

New Article: Macroscopic Fundamental Diagram and Public Transport

Changing Course in Urban Transport

A brand new article in Transportation Research Part C: Emerging Technologies examines a macroscopic fundamental diagram (MFD) and how it is applied to bi-modal urban networks. "A three-dimensional macroscopic fundamental diagram for mixed bi-modal urban networks," by (ITS alum) Nikolas Geroliminis, Nan Zheng,and Konstantinos Ampountolas investigates existence of a three-dimensional vehicle-flow MFD for bi-modal network.

Recent research has studied the existence and the properties of a macroscopic fundamental diagram (MFD) for large urban networks. The MFD should not be universally expected as high scatter or hysteresis might appear for some type of networks, like heterogeneous networks or freeways. In this paper, we investigate if aggregated relationships can describe the performance of urban bi-modal networks with buses and cars sharing the same road infrastructure and identify how this performance is influenced by the interactions between modes and the effect of bus stops. Based on simulation data, we develop a three-dimensional vehicle MFD (3D-vMFD) relating the accumulation of cars and buses, and the total circulating vehicle flow in the network. This relation experiences low scatter and can be approximated by an exponential-family function. We also propose a parsimonious model to estimate a three-dimensional passenger MFD (3D-pMFD), which provides a different perspective of the flow characteristics in bi-modal networks, by considering that buses carry more passengers. We also show that a constant Bus–Car Unit (BCU) equivalent value cannot describe the influence of buses in the system as congestion develops. We then integrate a partitioning algorithm to cluster the network into a small number of regions with similar mode composition and level of congestion. Our results show that partitioning unveils important traffic properties of flow heterogeneity in the studied network. Interactions between buses and cars are different in the partitioned regions due to higher density of buses. Building on these results, various traffic management strategies in bi-modal multi-region urban networks can then be integrated, such as redistribution of urban space among different modes, perimeter signal control with preferential treatment of buses and bus priority.

The full paper can be found here.

Assessing Airport Carbon Emissions

Descending through the LA smog

Much of the research about carbon emissions and transportation is focused on highways. A new article from the Journal of Air Transport Management proposes a model to examine carbon emissions and airports. Maria Nadia Postorino and Luca Mantecchini authors of "A transport carbon footprint methodology to assess airport carbon emissions," write:

Airports are important nodes in the air transport system, but also local sources of environmental impacts. Emissions of CO2 are among the most relevant ones because of their potential greenhouse effects. Many policies and guidelines have been identified at national and world level to reduce such kind of impacts. In this paper, a Transport Carbon Footprint methodology has been set to identify Unit Carbon Footprints (UCFs) linked to some identified emission macro-sources – i.e., land vehicles, on-ground aircraft, airport handling and terminal equipment – to compute the contribution of the single macro-source to the total amount of CO2. Particularly, UCFs due to transport activities have been defined according to some relevant transport variables. The computation of UCF values for a given airport allows computing both the contribution of each macro-source and also evaluating the effectiveness of transport-related actions aiming at reducing the carbon impact. The methodology has been applied to the airport of Bologna, in Northern Italy, and its UCF values for the identified macro-sources have been computed.

The full article can be found here

 

Travel Demand Forecasting: Beyond the models and into reality?

Chicago road network

Recently the State Smart Transportation Inivitiative (SSTI) asked if travel demand forecasts from U.S. DOT were accurate

Their answer is no

In the post, "U.S. DOT highway travel demand estimates continue to overshoot reality", Eric Sundquist examines the projections in FHWA's 2013 Conditions & Performance report. He finds that the estimates for VMT growth were 5-6% higher than reality. Concluding:

Had the report based estimates on more current historic data—e.g., VMT trends for 2003-13, which grew at one-fifth the USDOT’s 1995-2010 estimate—the cost estimates would have dropped by tens of billions more, reducing pressure on budgets while freeing up funds to bring the existing system to a state of good repair.

The accuracy of travel demand models and forecast predictions is not a new issue and more people are questioning the methodoloy. This year's TRB Annual Meeting featured a workshop on the issue The Next 50 Years in Travel Analysis: What We Don’t Know but Need to Know. The moderator, David T. Hartgen, mentioned a recent paper he wrote, "Hubris or humility? Accuracy issues for the next 50 years of travel demand modeling," in Transportation. Hartgen, examining 50 years of forecasting, describes problems with accuracy and ways to imrpove models. Definitely a paper worth reading. 

Everybody's a Tourist? Rethinking the Driver Population Factor

objects in mirror

A new paper, "Rethinking the Driver Population Factor," from ITS Berkeley's own Joshua Seeherman and Professor Alexander Skabardonis takes a look at the driver population factor currently used in the Highway Capacity Manual

Freeway analysis procedures in the widely used Highway Capacity Manual (HCM) include the input of a driver population factor (Fp), which allows the analyst to adjust the demand depending on the familiarity of drivers with the roadway. This adjustment is based on the assumption that unfamiliar drivers will drive at slower speeds with longer headways and that higher capacity would therefore be required. However, little research supports the use of the Fp, and the HCM cautions against the use of Fp unless the analyst is fairly certain the traffic stream is actually unfamiliar with the roadway. As an experiment, three bottlenecks in California were selected and analyzed during the weekday peaks and weekend afternoons in periods during which the traffic stream was likely to be nonlocal. The results showed that the changes in flow were minor at all three locations. Further research with additional sites and an increased awareness of the definition of familiarity will be required to confirm the results from this research.

The full paper can be found online in Transportation Research Record no. 2395 or you can look at the hard copy in the library. 

What makes people walk more?

walk

A new article from PLoS One asks the question, "What makes people walk more?" Actually, in, Richard H. Glazer et al ask - "Density, Destinations or Both? A Comparison of Measures of Walkability in Relation to Transportation Behaviors, Obesity and Diabetes in Toronto, Canada"

The design of suburban communities encourages car dependency and discourages walking, characteristics that have been implicated in the rise of obesity. Walkability measures have been developed to capture these features of urban built environments. Our objective was to examine the individual and combined associations of residential density and the presence of walkable destinations, two of the most commonly used and potentially modifiable components of walkability measures, with transportation, overweight, obesity, and diabetes. We examined associations between a previously published walkability measure and transportation behaviors and health outcomes in Toronto, Canada, a city of 2.6 million people in 2011. Data sources included the Canada census, a transportation survey, a national health survey and a validated administrative diabetes database. We depicted interactions between residential density and the availability of walkable destinations graphically and examined them statistically using general linear modeling. Individuals living in more walkable areas were more than twice as likely to walk, bicycle or use public transit and were significantly less likely to drive or own a vehicle compared with those living in less walkable areas. Individuals in less walkable areas were up to one-third more likely to be obese or to have diabetes. Residential density and the availability of walkable destinations were each significantly associated with transportation and health outcomes. The combination of high levels of both measures was associated with the highest levels of walking or bicycling (p<0.0001) and public transit use (p<0.0026) and the lowest levels of automobile trips (p<0.0001), and diabetes prevalence (p<0.0001). We conclude that both residential density and the availability of walkable destinations are good measures of urban walkability and can be recommended for use by policy-makers, planners and public health officials. In our setting, the combination of both factors provided additional explanatory power.

You can read the full article here because PLoS One is Open Access. Hat tip to Streetsblog for posting this

Electric Vehicles: Coast to coast, but will they impact emissions?

This week was a milestone in electric vehicle adoption and infrastructure in the US - a father-daughter team completed the first crosscountry roadtrip in a Tesla and it cost them $0 to recharge. What a bargain! Tesla Motors plans to expand their recharching network, so that future continental treks may take a more direct route.  

So as electric vehicles are slowly becoming more mainstream, the question is what impact will they have on greenhouse gas emissions? A paper recently presented at the TRB Annual Meeting looks at regional impacts in California.  Another recent study from NC State questions the impact electric vehicles have on emissions at all. Samaneh Babaee, Ajay S. Nagpure, and Joseph F. DeCarolis ask, "How Much Do Electric Drive Vehicles Matter to Future U.S. Emissions?". Their answer: probably not much given the emissions produced by electricity sources.

Modeling Escalator Capacity

Escalators are an under appreciated component of many public transportation systems. Can you imagine using the Dupont Circle Metro station without them? 

A recent paper from the Transportation Research Record examines the role of escalators in public transit systems. "Modeling the Practical Capacity of Escalators: A Behavioral Approach to Pedestrian Simulation" by Peter Kauffmann and Shinya Kikuchi looks at how escalators affect pedestrian behavior and public transit. 

Escalators are an essential mode of public transportation that enable people to travel vertically within a facility at a continuous, high flow rate. Despite the importance of the role of escalators in many facilities, little systematic analysis of the capacity of escalators has been conducted within the field of transportation engineering. A method is presented to calculate the practical capacity of escalators with a simulation based on pedestrian behavioral rules. The capacity of an escalator is defined traditionally only as a function of speed with speed-capacity curves defined by manufacturers or found in empirical studies. These methods do not consider pedestrian behavioral patterns and preferences such as following distance, passing aggressiveness, and other local factors. A rule-based model provides the flexibility to analyze conditions in various public facilities and to answer hypothetical research questions. Three major findings are reported. First, the practical capacity of escalators in commercial facilities such as shopping malls is significantly lower than the maximum capacity in a commuter facility such as a transit station, at only 20% to 40% of what is generally reported by manufacturers to provide for freedom of movement and pedestrian comfort. Second, the model shows that prohibition of walking on escalators can stream-line operations in emergency scenarios because it reduces variability in the system and increases flow, particularly during peak periods. Finally, contrary to some claims in the literature, uphill flow on escalators operates at a lower capacity than does downhill flow because of the presence of a "facial ellipse," the region directly in front of a pedestrian's face.

The full paper can be found online here. 

 

Built Environment Impacts on Individual Mode Choice

Downtown Houston

The built environment has an impact on mode choice. It's a topic ripe for study. In "Built Environment Impacts on Individual Mode Choice: An Empirical Study of the Houston-Galveston Metropolitan Area" by Jae-Su Lee, Jin Nam & Sam-Su Lee examines the built environment and mode choice for the city of Houston, publised in the most recent issues of the International Journal of Sustainable Transportation.

This study examines the impacts of the built environment measures based on two geographic scales, i.e., traffic analysis zone and one quarter-mile buffer on individual mode choice in the Houston metropolitan area. It is confirmed that they have significant impacts on mode choice in varying degrees. The models including the buffer-based measures are more reasonable than those with conventional zone-based variables for both home-based work and other trips. Finally, the elasticity estimates suggest the built environments are undervalued in the conventional transportation practices. Both land use and transport pricing measures should be considered complementary to control the demand for driving.

You can read the whole paper here

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