Massachusetts is Meeting Climate Change Head On

by Matt Mann, Reseach Program Coordinator

State Street, Boston – City Lab

As weather events become more extreme, MassDOT and Massachusetts communities, especially those on the coast, recognize their infrastructure is vulnerable. Coastal cities and towns are currently grappling with the extreme climate impacts of higher temperatures, increased extreme precipitation and greater amounts of sea level rise. All of these impacts are not new, they have slowly been occurring over the past century.  It is predicted these changes will accelerate and increases will happen over a shorter length of time (e.g. by 2030, the sea level could rise by 4”-8” (BRAG Report, 2016)).

MassDOT and Climate Ready Boston presented at the April 2018 MassDOT Innovation and Mobility Exchange on the impacts to transportation assets and infrastructure, and strategies to better accommodate climate change. Mia Mansfield, Climate Ready Boston, presented on goals to guide Boston’s future growth:

• Goal 1: Provide quality of life in accessible neighborhoods
• Goal 2: Drive inclusive economic growth
• Goal 3: Promote a healthy environment and adapt to climate change, and
• Goal 4: Invest in infrastructure, open space and culture

Associated with these goals are planning and implementation projects for creating resilient infrastructure and buildings, preparing communities, and protecting shorelines. The feedback from the public outreach on what types of flood ready improvements the public would like to see included expanding open space, berm development, and flood walls. Project areas Climate Ready Boston has focused on are East Boston, Charlestown, and South Boston. Mansfield spoke about this initiative saying, “The resiliency strategy embraces layered flood control and integrated green infrastructure measures that mitigate the effects of climate change, and create social, environmental, and economic benefits and value to the people of East Boston and Charlestown and to all who share in the health of the city and the harbor.”

The existing transportation assets will be impacted by more flash floods, landslides, and flooding. Further, increased precipitation could have adverse impacts on the infrastructure that helps move the water, especially on culverts. Hongyan Oliver, MassDOT Office of Transportation Planning, and Chris Dorney, WSP USA, presented on MassDOT’s multi-year statewide Climate Adaptation Vulnerability Assessment study. This study aims first to identify a prioritized set of MassDOT transportation assets throughout the Commonwealth that is at high risk for future inland flooding, and second to provide actionable scientific information for adaptive strategies, and future capital and project planning. This second goal begins on a broader planning level and then is developed through a detailed analysis of vulnerable assets. One challenge is mapping statewide future floodplains where vulnerable assets are located. With this challenge in mind, MassDOT is currently conducting a pilot mapping study on a watershed in western Massachusetts. The approach is to prepare georeferenced data, assign slopes, calculate current peak flows and 100-year flows, elevations, and floodplains, and evaluate the asset exposure. Procedures for floodplain mapping will include developing an instruction manual, applying the data management protocol, and automating parts of the process for efficiency.

Next steps after that will include training additional MassDOT staff on the procedures, and applying the pilot study procedures and lessons learned from all other watersheds in the state and sharing the results and data with stakeholders.  Eventually, this important information and these strategies can then be incorporated into MassDOT’s project prioritization, capital planning, asset management system, and emergency preparedness procedures.

Pre-signals for Transit Priority

Transit preferential treatments can reduce transit delay and therefore improve the efficiency and reliability of transit systems. Examples include dedicated bus lanes, queue jump lanes, and transit signal priority. However, these treatments are not always feasible due to lack of funding or space. In addition, they can often have detrimental impacts on other users of the system. Sustainability goals that are set by a lot of planning and transit agencies demand solutions that more efficiently utilize existing infrastructure and capacity while providing priority to transit vehicles.

Pre-signals allow for provision of priority to buses traveling on dedicated bus lanes by taking advantage of existing infrastructure and utilizing intersection capacity more efficiently. Pre-signals are additional signals placed upstream of signalized intersections to facilitate provision of some level of priority to buses, as well as other modes, by allowing them to bypass standing queues of cars. Typically, operating pre-signals require the existence of at least two lanes in the direction of travel.

However, recent work has suggested that pre-signals can aid in the temporary utilization of contra-flow lanes for transit priority provision for single lane approaches [1]. In particular, pre-signals are used upstream of the main intersection signals to allow the bus to jump the car queues and be at the front of the queue at the main signal. Pre-signals are used in combination with dedicated bus lanes when there is a need to end the bus lane in advance to allow cars to discharge from the intersection using all lanes. For example, as seen in Figure 1 the dedicated bus lane ends at some distance upstream of the intersection to allow cars to use all three lanes while discharging from the intersection.

Figure 1. Pre-signal at a three-lane approach with a dedicated bus lane.

The pre-signal works as a regular signal and is coordinated with the main signal to utilize maximum capacity. While the main signal is red, cars receive a red light at the pre-signal and are queued upstream of it. This ensures that a bus arriving during the red period can move to the stop line at the main signal and discharge immediately when the main signal turns green. Cars receive a green pre-signal such that no gaps are created in the traffic stream, and no green time at the main signal is lost when buses are not present. Regardless of the main signal’s phase, a bus approaching the intersection will trigger the pre-signal to turn red for cars, allowing the bus to move to the main signal without encountering conflicting maneuvers from cars.

An example of real-world pre-signal operations can be seen in this video. The video presents the operation of a pre-signal along Langstrasse in Zurich, Switzerland. A dedicated bus lane and one lane for cars exist upstream of the intersection but merge into a single mixed-use lane just upstream of the signalized intersection. A pre-signal at the location of the merge provides priority to buses when approaching the main signal. The pre-signal turns red when the bus is detected approaching the intersection. As a result, the bus travelling on the bus lane can bypass the queue of cars and enter the mixed-use lane at the intersection before the cars arrive. As soon as the bus bypasses the standing queue of cars, the pre-signal turns green again so that cars can proceed through the intersection after the bus.

The concept of pre-signals was first introduced to address lost time due to acceleration and perception/reaction time at the onset of green at signalized intersections and the first pre-signals were installed in Dusseldorf, Germany in 1954 [2]. This first study found that if there are only cars in a traffic stream, the equivalent of approximately 4 seconds of additional green time can be gained at intersections with the use of this type of pre-signal. More recent work has explored the use of pre-signals to increase intersection capacity by resolving various types of vehicular conflicts (e.g., between left and through moving vehicles that are either conflicting or compete for green time at the main signal) that would otherwise occur at the signalized intersection downstream [3,4]. A theoretical analysis of pre-signals for transit priority was first presented by Wu and Hounsell [5]. However, their proposed implementation included a constant pre-signal operation regardless of the arrival of a bus. To the best of our knowledge, real-world implementations of pre-signals are limited. A few locations are known in London, operating in a fashion similar to the one described in [5] and one location has been noted in Zurich, Switzerland.

We are currently working on identifying domains of application for implementation of individual transit preferential treatments or combinations of those for a variety of operating conditions for traffic and transit. Click here for a relevant presentation. 

By: Eleni Christofa, Ph.D., Assistant Professor, UMass-Amherst and S. Ilgin Guler, Ph.D., Assistant Professor, The Pennsylvania State University 

[1] Guler, S.I., Gayah, V.V. and Menendez, M., 2016. Bus priority at signalized intersections with single-lane approaches: A novel pre-signal strategy. Transportation Research Part C: Emerging Technologies, 63, pp.51-70.

[2] Von Stein, W., 1961. Traffic flow with pre-signals and the signal funnel. Theory of Traffic Flow, Elsevier, Amsterdam.

[3] Xuan, Y., Gayah, V., Cassidy, M. and Daganzo, C., 2012. Presignal Used to Increase Bus-and Car-Carrying Capacity at Intersections: Theory and Experiment. Transportation Research Record: Journal of the Transportation Research Board, (2315), pp.191-196.

[4] Xuan, Y., Daganzo, C.F. and Cassidy, M.J., 2011. Increasing the capacity of signalized intersections with separate left turn phases. Transportation Research Part B: Methodological, 45(5), pp.769-781.

[5] Wu, J. and Hounsell, N., 1998. Bus priority using pre-signals. Transportation Research Part A: Policy and Practice, 32(8), pp.563-583.