Diverging Diamond Interchanges and their Relation to Sustainable Design

Transcription

1 Diverging Diamond Interchanges and their Relation to Sustainable Design FINAL SUBMITTAL MARCH 0 th, 0 Word Count:, (, Paper + Abstract + Title Page; Exhibits,,00 words) 0 Jason Starr, PE Associate HDR Engineering 0 Cattlemen Road Suite 00 Sarasota, FL - -- Jason.Starr@hdrinc.com Scott Johnson*, PE, ENV SP Associate HDR Engineering 00 th Ave. NE Suite 00 Bellevue, WA Scott.Johnson@hdrinc.com *Lead Author

2 Abstract Diverging Diamond Interchanges and their Relation to Sustainable Design Sustainability is an increasingly important aspect of planning, design, and construction. With up to DDIs being in operation within the United States by the end of 0, we now have the ability to look back on a number of designs and see what impact they had on the environment compared to traditional interchange solution methods. This paper and presentation will cover the role of sustainability and how it is being accomplished with DDI design. Through case studies we will examine a list of categories comparing different sustainable metrics that are used in the Envision Sustainability Rating System. The advantages DDI s provide related to reduced ROW, reduced total lanes through an interchange which require less materials to construct, and reduced delays for vehicles leading to lower emissions all have an impact to environmental sustainability. Reduced vehicle conflict points, safer sidewalk crossings and enhanced bicycle lane designs within DDI s provide a sustainable element related to the quality of life. We will also examine the advantages DDI s provide as low-cost / low-impact temporary solutions for maintenance of traffic and funding shortages. There are many more advantages that DDIs provide to sustainable design. Through an awareness of the sustainable advantages that DDIs provide we hope to further push the envelope for creative DDI design and low-impact solutions to transportation problems. Jason Starr, PE Associate HDR Engineering 0 Cattlemen Road Suite 00 Sarasota, FL - -- Jason.Starr@hdrinc.com Scott Johnson*, PE, ENV SP Associate HDR Engineering 00 th Ave. NE Suite 00 Bellevue, WA Scott.Johnson@hdrinc.com

3 Diverging Diamond Interchanges and their Relation to Sustainable Design Sustainability is an increasingly important aspect of planning, design, and construction. The earth is closing in on the warmest year on record, resources will continue to become scarce, and urban densification has limited the available land to build or expand interchanges. These restrictions reduce the ability to improve mobility at major roadway crossings. As the economy emerges from the recession, society has been trained to look for efficient and cost effective ways to accomplish goals. In the United States, up to Diverging Diamond Interchanges (DDI) will be opened to traffic by the end of 0. Even with the limited number of case studies available, we have begun to see advantages of DDIs in the field of sustainability when compared to more traditional interchange types. This paper takes a closer look at interchange sustainability and specifically the advantages that can be provided by implementing DDIs instead of traditional diamond interchanges. 0 Figure # WHERE? For this analysis, select case studies were chosen for locations where a DDI design showed significant sustainability advantages over traditional diamond interchanges. These designs provide a snapshot of the benefits that can be obtained from implementing a DDI. They also aim to further the acceptance of DDIs in everyday transportation interchange design. Locations analyzed in this paper include the following: College Drive and I- DDI Cheyenne, WY (Constructed 0)

4 Figure # This DDI is one of, if not the, lowest volume DDI in the United States. It is in rural Wyoming at an interchange that serves a high volume of trucks. The project location s existing condition was a diamond interchange with a -lane cross section and sidewalk facilities on the north side of the roadway. Through traffic analysis and design, the interchange modifications that were ultimately constructed converted the -lane diamond interchange to -lane DDI, thereby reducing the section by -lanes. This modification to the cross-section and interchange type drastically improved mobility at the interchange, especially for the trucks. I- & S Meridian Road Boise, ID (Concept Not Advanced) 0 Figure # The concept for a DDI was considered at the interchange of I- and S Meridian Road as a solution to a congestion problem. There is a water park in the southwest quadrant of the interchange which produces heavy directional traffic flows at the interchange. The concept proposed to use the curvature of the DDI to locate the new bridges outside the existing bridge footprint. Because the new bridges would be located in this way, it would allow for construction of the bridges to occur outside the existing roadway limits and complete bridge construction prior to any shutdown of the cross-street. Once the bridges were built in this proposal, the connections would be constructed over a short term closure. This interchange concept is an

5 example of a solution that decreases maintenance of traffic impacts to the travelling public through design advantages that a DDI can provide. University Parkway Sarasota, FL (Final Design) 0 0 Figure # The University DDI will be the largest DDI in the world when it goes to construction. There are -lanes eastbound and -lanes westbound, creating an -lane DDI. The interchange has extremely high volumes and very unique constraints that helped solidify the DDI as the proposed alternative. These interchanges were chosen because of their difference in size, configuration, and constraints. In practice, every scenario is not the same. These scenarios provide examples of the key features that DDIs possess which help them advance sustainability. SUSTAINABILITY METRIC There are many definitions explaining sustainability, and there are many ways of rating those definitions. To evaluate the sustainability of a DDI we have chosen to utilize a certified rating system. Envision TM is a sustainability rating system developed through collaboration between the Zofnass Program for Sustainable Infrastructure at Harvard University Graduate School of Design and the Institute for Sustainable Infrastructure. Envision TM provides metrics for rating different infrastructure projects of varying shapes and sizes and was chosen to be used in this analysis because of the adaptability to various project types and sizes. For an analysis of how DDIs compare to traditional diamond interchanges, we have chosen categories from the Envision TM rating system. This paper provides a comparison of sustainability features and examines how certain areas of DDIs excel in providing a more sustainable interchange. The categories we are evaluating are: Quality of Life, Leadership, Resource Allocation, Natural World, and Climate and Risk. Quality of Life: This category is based on people and how they are affected by the project as individuals and as a group. Good scores in the category can be attained by having a project that minimizes pollution, minimizes noise and vibration, enhances public health and safety, improves community mobility and access, and encourages alternative modes of transportation.

6 0 Leadership: The category focuses on the involvement of the project team and how the team s leader champions the project. It involves setting up the project for success by implementing a long term vision and extending the useful life of infrastructure with minimal cost and resources. Resource Allocation: The resource allocation category focuses on minimizing the materials that are used to construct the project, reducing material that needs to be taken off-site during construction, reducing energy consumption to construct the project and to maintain the project in the future, and protecting water systems. Natural World: To successfully accomplish the goals of the natural world category, the project preserves habitats, avoids environmental impacts, manages storm water and polluted runoff, and avoids impacting floodplain function. Climate and Risk: The Climate and Risk category is about the earth and how to protect it through reduced carbon and air pollution emissions. It also focuses on how to develop a project that meets short term needs and is forward compatible to long term goals. Finally, this category values reducing risk in the project. DDI SUSTAINABILITY ANALYSIS DDIs present some unique characteristics that score well on the sustainability scale. This analysis of different DDIs, and how they excel in the different categories, was done using both qualitative and quantitative methods depending on applicability. Each DDI location and overall project scenario is different, and this analysis will not be true for every project. The intent of the analysis was to provide validation that DDI s can provide a more sustainable solution to our everyday transportation infrastructure needs. 0 0 Quality of Life There are three areas of the Quality of Life category in which DDIs are advantageous in the field of sustainability. The categories of Safety, Noise and Vibration, and Community Mobility and Access score very highly with a DDI design. DDIs are commonly used as a solution to transportation congestion problems. They typically increase throughput by changing from a or phase signal (used in traditional diamond interchanges) to a phase signal (used in DDIs). The advantage of a phase signal is that there are fewer transitions per cycle. This equals less all-red time in which no vehicles are moving. The Community Mobility and Access category receives a high score from this signal advantage because a lower rate of congestion and shorter delay improves users mobility through the infrastructure. Safety for vehicles, pedestrians, and bicycles is greater traveling through a DDI than through a traditional diamond interchange. Because DDIs are still relatively new, more information needs to be gathered. However, early results show that safety is increased. There are two specific

7 reasons for the enhanced safety of users on DDIs: conflict points and the severity of conflict points. Figure # The more conflict points that exist in an interchange, the more opportunities there are for conflicts to occur. The greater the angle of impact, the greater the magnitude of the conflict. The figures (# and #) show the major conflict points that occur on a DDI and on a traditional diamond interchange. There are a total of vehicular conflict points in a DDI compared to 0 vehicular conflict points in a traditional diamond interchange. By basing the conflict on opportunity, there is a % greater chance for an incident with a traditional diamond interchange. This comparison is consistent whenever contrasting a DDI with a traditional diamond interchange.. 0 Figure # The DDI conflict points also have the advantage of being less severe. The closer the angle of conflict is to 0 degrees, the more severe the conflict will be. The diamond interchange consists of multiple conflict points with 0 degree angles, creating more severe collisions due to momentum. The DDI conflict points at the ramps and crossings vary between 0 and 0 degrees. The difference in the angle results in less severe conflicts in DDIs and presents a benefit to the travelling public.

8 On both DDI and traditional diamond interchanges, there are four pedestrian conflict points. Public safety of pedestrians is higher on DDIs because of the difference in crossing distance and the single direction of traffic that needs to be crossed. The design of the DDI allows a pedestrian to cross only one direction of traffic. The movements are also signal protected. The pedestrian will only have to check one direction for oncoming traffic before crossing the street. This results in fewer conflicts between pedestrians and vehicles running red lights. The other benefit of pedestrian crossings on DDIs is that the crossing distance is typically 0% shorter than a diamond crossing and thus results in a 0% reduced chance of conflict. DDIs also present a higher score in sustainability for the Quality of Life category in Noise and Vibration. In noise analysis for transportation projects, the most likely location for intense noise is at intersections. This is due to the noise vehicles create by braking and accelerating. The DDIs still have the same or more traffic volume moving through the intersections. However, they drastically decrease the amount of traffic that needs to stop for turning movements. The main function of a DDI is to allow free flow left-turn movements to reduce delay. This decreases the vehicles stops and starts and reduces the noise pollution caused by this action. This is especially significant in a -lane DDI such as the College Drive Project because the configuration allows for the ramp traffic to not stop, and only yield, when exiting the freeway and entering the DDI with a left or right turn. 0 Figure # Leadership: The DDI is still a new and unknown concept for the vast majority of the public. This type of interchange needs a strong champion from the public agency to push it through the concept process and present it to the public at large. Because there are not a lot of professionals with experience designing, constructing, and maintaining DDIs, it is sometimes a daunting task. The leadership category of sustainability is present on all DDI projects because it is still new. DDIs can benefit the community in other ways as well. DDI projects can present an opportunity to extend the useful life of infrastructure for a fraction of the cost and save taxpayer dollars. They also present a design that allows for creative maintenance of traffic during construction.

9 The College Drive DDI is an excellent example of how the DDI was a sustainable solution which allowed an existing bridge to be retrofitted. New approaches were constructed to extend the service life of the interchange by 0 years. The bridge was nowhere near its construction life when the project started. By implementing the DDI and retrofitting the bridge to move the sidewalk from the edge of the bridge to a center median, the projected service life of the interchange was extended to the date when the bridge will be replaced in the future. DDIs have curves that are used to develop the crossing movements in the interchange. These curves can be adjusted and tweaked to create many different variations of DDIs. The DDI concept in Boise at I- presented an opportunity to use those curves for maintenance of traffic purposes. Constructing bridges is usually a very complex portion of an interchange project. Great lengths are taken in high use interchanges to maintain traffic movement during construction. A project in Bellevue, WA designed by HDR even constructed the traditional diamond interchange bridge to the side of the existing bridge and rolled it into place upon completion to avoid costly traffic shutdowns. The DDI is able to use the curves to move the location of the bridge either under or over a freeway. By constructing the future bridges on either side of the existing bridge, the DDI allows the current interchange to stay open to traffic until the bridge construction is complete. Notice in Figure # how the bridges are outside the existing facilities. 0 Figure # This presents a reduced impact to the travelling public during construction. It is therefore a sustainable alternative to shutting down traffic and creating additional traffic delays. Resource Allocation and Natural World: Every project requires material to construct it. The less material that is used to construct a project, the more material is available for other uses. This is the core tenet of the resource allocation sustainability criterion. DDIs create -phase signals instead of the typical - phases

10 that exist on diamond interchanges. Because of the elimination of a phase in the signal, a DDI is able to dedicate more green time for all movements. This extra green time allows the capacity of the lane to be increased in relation to a diamond. If a DDI is 0% more efficient than a -lane diamond scenario, a DDI will save construction of a single lane in each direction. If the DDI is lanes and is 0% more efficient, that allows for a reduction of roughly 0% of the material needed for constructing the interchange. The University DDI will be the largest DDI in the world when it is constructed. This interchange consists of total lanes and would consist of or more lanes in a typical diamond interchange. That s over lanes that are not being constructed because the DDI is more efficient. In addition to material savings at the time of construction, future resource savings will occur due to reduced maintenance. Fewer lanes of pavement will equate to fewer upkeep needs. Figure # 0 This same principal ties in nicely with the sustainability benefits a DDI provides to the Natural World category. The Natural World category takes into account the impacts on the environment. All impervious roadways with traffic on them are considered to be pollution generating impervious surfaces (PGIS). This means the runoff of storm water is a pollutant to the environment. By decreasing the total surface area that vehicles are driving on, we are able to reduce both ) the amount of impervious surface area created by the project, and ) the amount of pollutants that need to be filtered out of the roadway runoff. This has benefits to the storm water system on the interchange by possibly reducing the pipe sizes in the system, the detention required for flow control, and the amount of treatment facilities needed. One other advantage of DDIs is the ability to use a reverse crown cross section. Typical roadways are crowned to the outside to shed runoff to the shoulders. Because a DDI has space in the median, the roadway has the opportunity to be sloped to the center median and collect the runoff at one location. This eliminates the need for a parallel system to collect runoff in two locations. An example of a reverse crown cross section is shown in Figure #.

11 Figure # 0 Climate and Risk: The climate is unpredictable due to the rising temperature of Earth. Greenhouse gas emissions are cited as the main culprit that researchers point to when trying to explain the change in the climate. DDIs decrease the amount of greenhouse gas emissions that occur at an interchange in multiple ways. The first way is that they require less material to construct. As discussed previously, a DDI can sometimes need fewer lanes than a traditional diamond interchange. Because of this, less construction material (such as HMA or concrete) is needed. Therefore, the greenhouse gas emissions that would be created from producing these materials are eliminated. There also is no transport of that material which eliminates more greenhouse gas emissions. The second manner in which DDIs avoid greenhouse gas emissions is by reducing vehicle delay at the interchange signals. By reducing delay at the interchange signals, DDIs reduce the amount of time that a vehicle sits on the off-ramp or at the stop light waiting to continue through the interchange. Those delay seconds that are saved equate to time that a vehicle is idling and burning fuel without moving. These emissions are wasted. Through the reduction in delay that a DDI can provide, it also provides a reduction in greenhouse gas emissions. CONCLUSION The DDI offers many sustainability features that improve on the aspects of a traditional diamond interchange. This is validated by comparing DDI s and traditional diamonds with the Envision TM rating system. Each project has different conditions, so the benefits cannot be applied as a rule. However, the DDI does outperformed the traditional diamond on numerous occasions. These advantages included being able to influence the quality of life the public experiences, promote leadership in the community, conserve valuable resources on our planet, protect the environment and reduce a project s impacts to it, and lessen the possible influence our projects have on the climate. DDIs present a transportation solution to congestion problems. They also offer a sustainable solution to interchange projects.