This week’s Friday TRANSOC Seminar has Vikash Gayah, Ph.D. candidate, University of California, Berkeley, presenting “The Aggregate Effect of Turns on Urban Traffic Networks.”
This research creates and uses macroscopic traffic models to describe the aggregate behavior of vehicles on urban street networks. Insights gained from these models can then be used to design network-wide policies that may increase the ability of these networks to serve vehicle-trips. In particular, this work focuses on the turning maneuvers that exist in networks with multiple routes. The presence of multiple routes and turning maneuvers are found to have two effects on aggregate vehicle behavior: 1) they cause unstable and inefficient behavior when a network is congested; and, 2) they may reduce maximum vehicle flows across the network. Fortunately, this work finds that limiting the rate at which vehicles are allowed to enter a network and providing drivers with real-time information on current traffic conditions can help mitigate the first effect and allow the network to operate more efficiently. It is also found that the second effect may not always be harmful—lower network flows do not necessarily result in decreased network efficiency if the lower flows are accompanied by more direct vehicle routing. In fact, two-way networks, which accommodate conflicting left-turns and result in lower maximum vehicle flows than one-way networks, are found to serve trips at a higher rate because drivers travel shorter distances on average. Thus, in many cities, maximum network efficiency can be improved by converting one-way streets to two-way operation.
The seminar will take place at 4:00 PM in534 Davis Hall. Please join us for a TRANSOC-sponsored Cookie Hour in the ITS Library at 3:30 PM.
Today’s TRANSOC Friday Seminar has Nikolas Geroliminis, PhD., Assistant Professor, Urban Transport Systems Laboratory, École Polytechnique Fédérale de Lausanne (EPFL) presenting “The M6 of traffic systems: Macroscopic Modeling, Monitoring and Management of Multimodal Mobility.”
As more people and transport modes compete for limited urban space to travel, there is a need to understand how this space is used for transportation and how it can be managed to avoid traffic congestion. Our research seeks to shed some light in the modeling, planning and management of traffic flow for overcrowded cities with multimodal transport. We develop methodologies to model and understand the collective behavior for different types of multi‐modal systems, with emphasis in conflicts for the same road space (e.g. mixed traffic of buses and cars). The goal is to develop optimization tools on how to distribute city road space to multiple modes and to understand the level of accessibility for cities of different structures. We also investigate what type of real-time active traffic management schemes (congestion pricing, vehicle restriction, large scale traffic signal control) can improve mobility measures in a city. Until now traffic control systems in urban areas are locally programmed with little control over the impact of a micro-scale response to the macro-scale level. We build a hierarchical feedback control network of multiple levels. The validation of the modeling methodologies and the traffic management schemes are conducted in various and complex city structures scenarios using data from field experiments advanced micro-simulations.
The seminar will take place today 4:00 PM in 406 Davis Hall. Please join us for a TRANSOC-sponsored Cookie Hour in the ITS Library at 3:30 PM.
Tomorrow's TRANSOC Friday Seminar features Ph.D. candidate Ilgin Guler presenting, "Strategies for Sharing Bottleneck Capacity among Buses and Cars."
Buses that operate in mixed traffic can be impeded by car congestion, leading to unreliable and slow bus service. Conversely, buses that frequently stop to serve passengers can interfere with the movement of cars. To address these issues, exclusive bus lanes have often been used to segregate buses from other traffic. These exclusive bus lanes provide a means for buses to bypass car queues, thereby increasing bus speed and potentially decreasing the total person hours travelled on a network. In urban settings exclusive bus lanes are typically deployed by converting an existing general purpose lane to bus use only. However, in cases where bus flow is low, these lane conversions can increase the queuing and delays to cars. The problem is particularly acute at roadways bottlenecks, since cars now discharge from one less lane, even when the bus lane is unoccupied.
This research examines strategies for judiciously inserting cars between buses in ways that minimize the losses in a bottleneck’s car carrying capacity when bus demand is low. The idea entails sharing lanes among buses and cars in the vicinities of critical bottlenecks; and to have these shared lanes augment exclusive bus lanes that are deployed elsewhere throughout the network. The specific type of sharing strategy to be used near any given bottleneck would depend upon its operating conditions. In all cases the goal is to prioritize bus travel while minimizing the additional delays that this prioritization imparts to cars. Analysis unveils the ranges of bus demands for which the shared‑lane strategies are superior to ordinary lane conversions. We find that the shared-lane strategies have merit in many instances. Implementing these strategies for a real-world case study in Amman, Jordan produces promising outcomes: simulation analysis indicates that the delay savings to cars brought by the lane–sharing strategies are considerable. The proposed ideas can help increase the political acceptability of bus priority systems and promote public transportation in cities of various sizes.
The Seminar will be from 4-5pm in 406 Davis Hall. There will be no cookie hour precedding it this week, so you'll need to sort out your sugar fix some other way.
The study is concerned with the vehicular interactions that arise when carpool and regular vehicles are segregated in their own lanes. Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent regular-use lanes.Thanks to this smoothing effect, we find in many cases that the carpool lanes – even when underused themselves – can benefit travelers in the regular lanes.Ironically, the regular-use lanes are often damaging to the carpool-lane travelers. We find that the vehicle speeds in a carpool lane are negatively influenced by both growing use of that lane and diminishing vehicle speeds in the adjacent regular-use lane.The findings do not bode well for a new US regulation stipulating that most classes of Low-Emitting Vehicles (LEVs) are to vacate slow-moving carpool lanes.Analysis shows that relegating some or all of these vehicles to regular-use lanes can significantly add to regular-lane congestion; and that despite the reduced use of the carpool lanes this, in turn, can also reduce the speeds of those vehicles that continue to use the carpool lanes.Constructive ways to amend the new regulation are discussed, as are promising strategies to increase the vehicle speeds in carpool lanes by improving the travel conditions in regular lanes.
The seminar will take place from 4-5 pm in 406 Davis on November 18. Please come to TRANSOC's Cookie Hour preceeding the seminar at 3:30 pm in the library.
Last week the Arizona DOT filed an application with FHWA to impose a toll on the 29.4 mile stretch of Interstate 15 within Arizona's border, which links Nevada and Utah. Utah Governor Herbert strongly opposes such a move.
"I strongly oppose any plans to levy tolls on Arizona's portion of I-15, or on any portion of I-15," said Governor Herbert. "Every state pays into the Highway Trust Fund, and every state receives money from the Highway Trust Fund to maintain the segments of the Interstate Highway System inside their respective borders. Arizona cannot pick and choose which parts of our national interstate network it wants to maintain. If Arizona has been negligent in its maintenance of I-15, it should not try and foist its responsibility onto highway users or neighboring states who already pay into the system with their own tax dollars."
“Our results show that everybody is worse off with the program’s ending,” said Cassidy. “Drivers of low-emission vehicles are worse off, drivers in the regular lanes are worse off, and drivers in the carpool lanes are worse off. Nobody wins.”
“As vehicles move out of the carpool lane and into a regular lane, they have to slow down to match the speed of the congested lane,” explained Jang. “Likewise, as cars from a slow-moving regular lane try to slip into a carpool lane, they can take time to pick up speed, which also slows down the carpool lane vehicles.”
A Northeast Corridor train derailment disrupted New Jersey Transit service to and from New York earlier this week. The derailment and resulting commuter nightmare has some transit riders calling for officials to reconsider the decision to kill the Mass Transit Tunnel. Groundbreaking for that project, which would have resulted in a second transit tunnel under the Hudson River, was held in 2009, but New Jersey Gov. Chris Christie killed the over-budget project in October of last year. The governor has indicated a willingness to consider other projects to increase transit capacity between New Jersey and New York. An Amtrak derailment earlier today is causing further headaches for NJ Transit.
The pinnacle of transportation-related annoyance may be that not only does rubbernecking take place along the route where the accident happens, but it can even cause severe jams in the lanes going the opposite direction. So a few years ago I had what I thought was a bright idea: how about setting up screens at accident sites to hide the scene and prevent gaping?
Finally, somebody is trying out this idea in practice. The Highways Agency in the U.K. has tested such screens. (For more see this, this, this, and this, which leads you to several other links.) The bottom line is that the screens are not perfect; for example, the barriers to which the screens have to be attached vary in size, which creates problems; the screens are vulnerable to wind; the decision about whether to deploy them must be made very rapidly; they have to be able to be set up quickly and safely, etc. Thus they are not suitable for all accident sites. However, as the links above indicate, test results have shown they are effective.
Hopefully there will be more follow up studies on the issue. Will screens be coming stateside soon?