Congestion

Institute of Transportation Studies Friday Seminar: Lane Changing - Mysteries on Behavior and Modelling

Changing lanes

This week's Friday Transportation Seminar is about ellusive lane changing behaviors. Victor Knoop, Assistant Professoor of Transport & Planning at TU Delft will present, "Lane Changing - Mysteries on Behavior and Modelling."

Traffic congestion often is related to lane changes - at a lane drop bottleneck, on ramp, or weaving section. It is therefore essential to have a good description of the lane change maneuvers performed by drivers. Whereas much attention has been given to car-following behavior (how much distance do people keep), lane changing did not get the same amount of attention. This seminar will touch upon three aspects related to lane changing. Firstly, a large-scale data analysis shows that simple concepts of trying to go to a faster lane combined with gap accepting does not provide a satisfactory model. In the seminar outcomes of the data analysis are shown at it is discussed what can be learned from it. Secondly, calibration and validation are required for any model, but there is no standardized method for calibrating lane-change models. It will be shown that the methods have been chosen carefully. Thirdly, the differences in driving strategy between drivers with regard to lane changing are discussed.

The Friday Transportation Seminar takes place on September 19, 2014 from 4:00-5:00 PM in 290 Hearst Memorial Mining Building. Cookie Hour immediately precedes it at 3:30 PM in the same location. (Note: Cookie Hour is not in the library!) There will also be a no-host Happy Hour at LaVal's at 5:00 PM.

Institute of Transportation Studies Friday Seminar: Lessons Learned from Spatiotemporal Studies of Freeway Carpool Lanes

WIDE LOAD

Late August means the end of summer is nigh, students are back, classes are in session, and it's the return of the Friday Transportation Seminars. This semester there are some changes to the seminars - Cookie Hour and the seminar will take place in the same location in 290 Hearst Memorial Mining Buidling. We also encourage you to follow along (and participate) with the Twitter hashtag #itsberksem

This week's Friday Seminar features ITS's own Professor Michael Cassidy presenting, "Lessons Learned from Spatiotemporal Studies of Freeway Carpool Lanes."

The presentation explores how the segregation of distinct vehicle classes on a roadway can improve travel conditions for all of the classes. Insights come using freeway carpool lanes as case studies. Spatiotemporal study of real sites shows (i) how the activation of a continuous-access carpool lane triggers reductions in vehicle lane-changing maneuvers, and (ii) how the reduced lane-changing can “smooth” and increase bottleneck discharge flows in a freeway’s regular lanes. Theoretical analysis predicts that, thanks to this smoothing effect, even underused carpool lanes can diminish both the people-hours and the vehicle-hours traveled on a freeway. Relevance to bus lanes is briefly discussed. Further insights come via critiques of certain practices that degrade the effectiveness of carpool lanes. Spatiotemporal traffic data reveal that a policy aimed at improving carpool-lane speeds has backfired, owing to a friction effect. The policy mandates the eviction of select fuel-efficient hybrid vehicles from carpool lanes. These evictions have caused queues to expand in regular lanes during the rush. And these expanded queues, in turn, slow vehicles in the adjacent carpool lanes. Spatiotemporal data further show that efforts to combat the friction effect by deploying limited-access carpool lanes can also backfire, because the designs for these lanes are prone to creating bottlenecks.

The Friday Seminar takes place on August 29, 2014 from 4:00-5:00 PM in 290 Hearst Memorial Mining Building. Cookie Hour immediately precedes it at 3:30 PM in the same location. (Note: Cookie Hour is not in the library!) There will be a no-host Happy Hour at LaVal's at 5:00 PM.

Friday Seminar: The Impact of Adverse Weather on Freeway Bottleneck Performance

Raindrops keep falling on my screen...

It's almost the end of the semester, but we still have two more Friday Seminars! This week is the penultimate seminar featuring Ph.D. candidate Joshua Seeherman. He'll be presenting his research, "The Impact of Adverse Weather on Freeway Bottleneck Performance."

Daily commutes in and out of major cities by automobile will likely encounter multiple locations of delay known as bottlenecks where demand exceeds capacity. It has been long perceived that the performance of these bottlenecks decrease when they are affected by adverse weather such as rain, snow, or fog. This project utilizes existing methodology to measure the discharge rate for four freeway bottlenecks in Orange County, California during both clear and adverse conditions. After confirming that the results agree with past literature, a new model will be proposed attributing different periods of bottleneck congestion during either wet, windy, or foggy conditions to specific weather characteristics. Generic results that can be applied to multiple sites will be shown which will validate the new proposal and hopefully provide guidance for other locations where wet weather is a significant source of delay.

The seminar will take place today, Friday May 9, 2014 from 4:00-5:00 PM in 212 O'Brien. (Note the room change!) Cookie Hour is on this week as well, at 3:30 in the library. 

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. 

Special Friday Seminar: Marco Nie "From Pricing to Cap-and-Trade"

MTA-Slides_0106

This week's TRANSOC Friday Seminar is at a special time - 11:00am - noon in 534 Davis. This week Northwestern University Associate Professor Yu (Marco) Nie will present on a cap-and-trade approach to congesiton management in "From Pricing to Cap-and-Trade: Analysis and Design of Quantity-based Approach to Congestion Management."

Traffic congestion continues to threaten economic prosperity and quality of life around the world. It is widely acknowledged that demand management is an indispensable ingredient in the recipe for solving the traffic congestion puzzle, and likely to be one of the more effective and cost-efficient if properly implemented. This research will explore a new and promising travel demand management strategy, inspired by various cap-and-trade schemes aiming to reduce greenhouse gas and air pollutant emissions. The cap-and-trade schemes considered in this research seek to couple direct travel demand restriction with a trading mechanism. Because such a scheme typically involves creating mobility credits and trading them in a market, it is also known as tradable credit scheme. In this talk we will examine a few key design issues involved in building such credit markets, including how to account for the effects of transaction cost and how to initially allocate credits, using various analytical models.

As noted above, the seminar is happening this Friday, October 25 2013, from 11:00am to noon in 534 Davis. We'll keep you posted about Cookie Hour. 

Wetter Stau: Examining Extreme Weather and Traffic Congestion in Germany.

Wenig Schnee - viel Chaos

Extreme weather events, such as blizzards or heavy rains, cause traffic congestion. A new article in the Journal of Advanced Transportation looks at the relationship in Germany. In "A study of the influence of severe environmental conditions on common traffic congestion features," Hubert Rehborn and Micha Koller use German traffic data to study the relationship on the Autobahn. 

On the basis of real traffic and environmental data measured on German freeways, we studied common features of traffic congestion under the influence of severe weather conditions. We have found that traffic features [J] and [S] defining traffic phases “wide moving jam” (J) and “synchronized flow” (S) in Kerner's three-phase theory are indeed common spatiotemporal traffic features. The quantitative parameters for both traffic phases [S] and [J] were investigated in a comparison of “ideal” weather conditions (good visibility and no precipitation) and severe weather situations (icy road, wind, precipitation, etc.). We showed spatiotemporal congested patterns in several space–time diagrams based on the Automatic Tracking of Moving Jams/Forecasting of Traffic Objects (ASDA/FOTO) model reconstruction for roadside detectors. A statistical study of traffic phase [J] parameters was presented, showing the average values and standard deviation of the quantities. Similarities and differences were analyzed, and some consequences for vehicular applications were discussed to cope with severe weather conditions.

The full article can be found here

Urban Gridlock

Chicago Gridlock

Gridlock is a fact of life in urban areas. Why is that? A new study explores the characteristics of urban gridlock, to better understand the condition and ways to ease congestion. From Transportation Research Part C: Emerging Techonologies, "Urban network gridlock: Theory, characteristics, and dynamics" by Hani S. Mahmassani, Meead Saberi, and Ali Zockaie tackles the issue. 

This study explores the limiting properties of network-wide traffic flow relations under heavily congested conditions in a large-scale complex urban street network; these limiting conditions are emulated in the context of dynamic traffic assignment (DTA) experiments on an actual large network. The primary objectives are to characterize gridlock and understand its dynamics. This study addresses a gap in the literature with regard to the existence of exit flow and recovery period. The one-dimensional theoretical Network Fundamental Diagram (NFD) only represents steady-state behavior and holds only when the inputs change slowly in time and traffic is distributed homogenously in space. Also, it does not describe the hysteretic behavior of the network traffic when a gridlock forms or when network recovers. Thus, a model is proposed to reproduce hysteresis and gridlock when homogeneity and steady-state conditions do not hold. It is conjectured that the network average flow can be approximated as a non-linear function of network average density and variation in link densities. The proposed model is calibrated for the Chicago Central Business District (CBD) network. We also show that complex urban networks with multiple route choices, similar to the idealized network tested previously in the literature, tend to jam at a range of densities that are smaller than the theoretical average network jam density. Also it is demonstrated that networks tend to gridlock in many different ways with different configurations. This study examines how mobility of urban street networks could be improved by managing vehicle accumulation and redistributing network traffic via strategies such as demand management and disseminating real-time traveler information (adaptive driving). This study thus defines and explores some key characteristics and dynamics of urban street network gridlocks including gridlock formation, propagation, recovery, size, etc.

The full paper can be found here.

Bottlenecks and the evening commute.

Motion

During the evening commute there are often bottlenecks as people try to get home on fixe routes with finite capacity. Vickrey's "Congestion Theory and Transport Investment" (1969) decribes the problem of commuters trying to pass the bottleneck. A recent paper, "The evening commute with cars and transit: Duality results and user equilibrium for the combined morning and evening peaks" by Eric Gonzales and Carlos Daganzo tackles the commute problem looking at both the evening and morning commute, since mode travel decisions are often made based upon the travel needs for the whole day. 

The paper then considers both the morning and evening peaks together for a single mode bottleneck (all cars) with identical travelers that share the same wished times. For a schedule penalty function of the morning departure and evening arrival times that is positive definite and has certain properties, a user equilibrium is shown to exist in which commuters travel in the same order in both peaks. The result is used to illustrate the user equilibrium for two cases: (i) commuters have decoupled schedule preferences in the morning and evening and (ii) commuters must work a fixed shift length but have flexibility when to start. Finally, a special case is considered with cars and transit: commuters have the same wished order in the morning and evening peaks. Commuters must use the same mode in both directions, and the complete user equilibrium solution reveals the number of commuters using cars and transit and the period in the middle of each rush when transit is used.

The whole paper can be found here

#BARTSTRIKE

 

At midnight July 1 2013, after failed negotiations between BART and its two main unions, BART workers went on strike. The strike has disrupted transportation throughout much of the Bay Area-  increasing commute times and traffic congestion. Many commuters are turning to the ferries, casual carpool, and rideshare. The more adventurous have opted for helicopters or yachts. While there has been the predicted mix of frustration, criticism, and selfpromotion on Twitter via #BARTstrike, it's still too early to gague the real impact of the strike on transportation. Some projections estimate the econmic impact to be $73 million a day as well as 16 million pounds of carbon. Some clues might be gleaned from the recently published, Subways, Strikes, and Slowdowns: The Impacts of Public Transportation on Traffic Congestion. Using data from the 2003 transit worker strike in Los Angeles, researchers show that transit relieves traffic congestion

Access Across America: How accessible are the jobs?

This week University of Minnesota's CTS issued a report about accessibility to job that includes an interactive map. Access Across America

Access Across America, a study by David Levinson, the R.P. Braun/CTS Chair in Transportation Engineering at the University of Minnesota, goes beyond congestion rankings to focus on accessibility: a measure that examines both land use and the transportation system. The study is the first systematic comparison of trends in accessibility to jobs by car within the U.S. By comparing accessibility to jobs by automobile during the morning peak period for 51 metropolitan areas, the study tells us which cities are performing well in terms of accessibility and which have seen the greatest change.

The full report can be found here. And here's the data!California is well represented with Los Angeles (1), SF-Oakland (2), and San Jose (6) all in the Top Ten.

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