Designing Complex Interchanges

INFRASTRUCTURE SOLUTIONS

Designing Complex Interchanges Constructing complex and regionally significant interchanges can affect hundreds of thousands of daily roadway users and stakeholders. Here are several best practices to mitigate the impacts.

Complex interchange reconstruction projects are of great concern to the public and businesses dependent on them. The potential impacts to the traveling public and local stakeholders must be anticipated and managed from project inception through construction close-out. By successfully managing and delivering these projects, owners bring impressive infrastructure improvements to the region and improve the lives of so many users. The project benefits include enhanced safety, improved operations and a modern and resilient transportation system.

This SOLVE piece focuses principally on three highprofile interchange projects and the solutions that helped the state agency achieve its objectives. The goal is to provide best practices used on the following successful New Jersey Department of Transportation interchange projects.

• Route 22/82/Garden State Parkway Interchange in Union, Union County • Route 18 Bridge over Route 1 in New Brunswick, Middlesex County • Route 3 at the Passaic River Crossing in Clifton, Passaic County & Rutherford, Bergen County Proactive management of the traffic, stakeholders, engineering risks and project costs will drive success on your project.

Route 18 Bridge over Route 1 in New Brunswick, Middlesex County

Kerri Tyerman, PE Sr. Project Manager on NJDOT's Route 22/82/Garden State Parkway Interchange project; nearly 30 years experience in transportation related design

Route 3 at the Passaic River Crossing in Clifton, Passaic County & Rutherford, Bergen County

1. Minimize traffic disruptions With hundreds of thousands of vehicles passing through a high impact interchange every day, the appropriate level of traffic data collection and modeling to best understand the local and regional dynamics is paramount. A microsimulation traffic model of the interchange such as VISSIM should be created at the onset of the project starting with available record data. In New Jersey, one of the best sources for record data is NJTMS, which compiles roadway and ramp counts from projects throughout the state. Supplemental data aggregation sources such as Streetlight, automated counts such as Miovision or automated traffic recorder (ATR) tube counts are used to calibrate the model. The model is then used to compare conceptual alternatives, evaluate traffic during construction conditions and confirm the sufficiency of detours and diversionary routes.

For large projects with regional impacts, a “meso” or “macro” simulation model such as Cube should also be considered to understand regional impacts.

The traffic analysis is invaluable to help stakeholders understand the project and secure public support. The background traffic information, supporting analyses, construction staging, traffic management strategies and stakeholder input should be documented in a Transportation Management Plan that will guide engineers and decision makers throughout the construction of the project.

Tim Severinsen, PE Sr. Project Manager on NJDOT's Route 3 at the Passaic River Crossing project; nearly 30 years experience in transportation related design

Steve Manera, PMP Sr. Project Manager on NJDOT's Route 18 Bridge over Route 1 project; nearly 40 years experience in transportation related design

A common challenge on interchange projects is to provide adequate work zones and working hours for the contractor while minimizing delays and safety risks to the traveling public.

One project that was severely constrained in these regards was the Route 18 Bridge over Route 1 in New Brunswick where the average daily traffic at this interchange exceeds 115,000 vehicles on each roadway and its proximity to the New Jersey Turnpike Interchange 9 and Rutgers University posed significant constraints. HNTB collaborated with NJDOT on an innovative approach to traffic management that included temporary median crossovers into one contraflow lane with opposing traffic protected by a concrete movable barrier curb (CMBC) system which provided the work zone necessary to replace the superstructure of two adjacent bridges. The CMBC was staged on the inside shoulder during the week and then quickly deployed with a transfer machine at 10 PM on Friday evening, creating the contraflow lane and providing the contractor with a wider work zone needed for large cranes to begin accelerated bridge construction (ABC) for demolition and installation of prefabricated superstructure units (PSU) within a 55-hour window over 10-weekends, opening the entire roadway to traffic by 5 AM Monday. With NJDOT approval, HNTB was able to design the project so that the Route 18 bridges would be rebuilt in 10 weekends during the summer, which avoided impacting Rutgers University traffic on weekdays or on any weekends with home football games.

2. Optimize stakeholder input With numerous stakeholders having their own unique special interests, listening to and understanding these individual interests is paramount. These unique stakeholders bring the highest risks, and their support of the project is vital.

Transportation and environmental regulatory agencies, railroads, local businesses and residents, environmental justice communities, bicycle/pedestrian advocacy groups, schools and emergency responders can all greatly influence your project’s design footprint and constructability. Identifying these critical stakeholders early and actively engaging is important. The design team may learn about jurisdictional or environmental constraints, community aesthetic concerns or special events and emergency evacuation routes that can affect maintenance of traffic. HNTB proposed additional plantings on the Route 22/Route 82/Garden State Parkway (GSP) interchange to improve the shielding of the highway from the residents based on comments received during the public outreach. Similarly, resulting from numerous Community Liaison Committee meetings, clear acrylic noise wall panels were constructed on the Route 3 Passaic River interchange project to maintain the resident’s views of the New York City skyline. During construction on the Route 22/82/GSP project, there were five separate and active construction projects in the immediate vicinity that required continuous coordination.

To address the larger public and all roadway users at these interchanges, a more widespread approach is needed. The typical communication and outreach methods of establishing a project website, leveraging social media platforms, holding Public Information Centers (virtual if necessary) and media outreach can be effective. One very powerful and effective tool to support an agency’s media relations is HNTB’s Public Involvement Management Application (PIMA). This web-based application enhances stakeholder experience and help agencies streamline their processes and public involvement action plans.

With the new mobile application, there is increased engagement and stakeholder sentiment, feedback and geospatial locations are easily identified and reported so agencies can pinpoint where within the community concerns are being raised. NJDOT has utilized PIMA on several projects including the Route 22/82/GSP interchange project.

3. Evaluate engineering risks & opportunities For complex and high-risk engineering challenges, selecting the right multi-disciplinary team of subject matter experts is paramount. With risks, also come opportunities. A risk is defined as an uncertain event that, when it occurs, the results can either be positive or negative. The opportunity lies with the positive outcomes. The NJDOT best practices include the risk register, constructability-risk assessment workshop and risk management plan that have proven to be very effective.

On the Route 18 bridge over Route 1 project, one key risk was that the contractor would not have sufficient staging areas to construct the deep bridge pier foundations. This challenge was solved by using micropile foundations, which was the first of its kind at NJDOT. Micropiles are small diameter drilled shafts installed with small equipment that have now become a new “opportunity” and solution for other NJDOT projects.

Constructability workshops are held by many agencies and are vital for project success. Engineers can learn from the contractor perspective on constructability. For the contractor, constructability is focused on schedule and cost. The process of going through “step by step” what is necessary to build the project will reveal the time, equipment, materials and ultimately costs. Determining access, safety, traffic control and other logistical needs is part of the process. Traffic models can be analyzed to validate that the temporary traffic patterns will not cause excessive delays that can become public relations challenges. HNTB performs intensive constructability reviews early in the design with ex-contractors and agency subject matter experts that identifies risks and cost-effective solutions that result in “biddable and buildable” projects.

These reviews provide another perspective to supplement the typical constructability checklists. On the Route 22/82/GSP project, precast concrete pavement slabs were proposed to be constructed during overnight hours because long term lane closures were unavailable for standard full depth pavement reconstruction.

4. Extend capital program funding With limited budgets to address outdated infrastructure around the country, constructable and cost-effective designs are paramount. Providing the right interchange designs that meet the Purpose & Need, improve safety and operations and address deficient or substandard infrastructure should be carefully evaluated against costs. Complex interchange reconstruction projects can cost in the hundreds of millions of dollars, and cost saving opportunities will always exist. HNTB actively seeks out these cost savings through its “Fish Finder” workshops that are held before a preferred alternative is selected. The right experts, including leaders from the public agency and ex-contractors, are brought in to identify strategies to reduce a job’s costs, risks and schedule while meeting the project goals in a different way.

The goal is for these third-party experts to perform exhaustive brainstorming sessions that act like a sonar to uncover big ideas, i.e., find a whale. The big fish is not found every time, but the process inevitably results in a much deeper understanding of the project’s goals, constraints and risks.

On a smaller scale, HNTB has proposed innovative designs for our New Jersey interchanges that save money, and the savings can then be recycled to fund other critical projects in the capital program. Constrained work zones with high volumes of vehicles result in less productive work and costlier bid prices.

To address this common challenge, the contractor can move the operations offsite, or minimize the time necessary in the work zone. HNTB implemented both solutions on the Route 18 over Route 1 interchange. Originally proposed as a deck replacement project, it was discovered early in the design phase that the existing steel girders were coated with lead-based paint on the top flange. Removing the deck onsite would have required time- and cost-intensive containment systems, air handling equipment and specialists. All of this could not be accomplished within the allowable lane closure hours. HNTB demonstrated that replacing the entire superstructure not only allowed for lead-based paint abatement to occur offsite but that road user costs would be significantly lower with this approach. After the existing superstructure was removed, the contractor installed PSUs and precast concrete deck and approach slabs during 10 weekends of construction. On the Route 22/82/GSP project, the new bridges were of similar design so that the beam fabrications would be simplified. Repetitive beam design meant keeping the size of the beams, fabrication and installation as routine as possible, under a single mobilization for the contractor, thus resulting in cost savings.

Conclusion Designing complex interchanges requires transportation agencies to proactively understand the entities most affected by the construction, namely the traveling public and identified key stakeholders. This vital information and communications should be documented in the transportation management and public involvement plans. The engineering team will also need to proactively identify all risks (and opportunities), constructability analyses, potential cost savings and innovative designs that result in the most successful outcomes for the project. HNTB has successfully partnered with NJDOT on complex interchange projects that have consistently delivered great value to the regional infrastructure users and stakeholders.

Team collaboration throughout the planning, design and construction is key. n

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