How Foamed Glass Aggregate is Being Used on Transportation Infrastructure at NJDOT: An Interview

NJDOT, like other State departments of transportation (DOTs), has become increasingly conscious of infrastructure’s environmental burdens and are seeking more environmentally sustainable materials in construction.  Recently, we spoke with Kimberly Sharp, Manager, Structural Design, Geotechnical Engineering and Geology, and Mohab Hussein, Project Engineer, Deputy Chief Technical, Geotechnical Engineering about NJDOT’s adoption of Foamed Glass Aggregate which serves an example of the deployment of an innovative, sustainable material.

To make foamed glass aggregate, crushed container glass is collected from recycling companies, finely ground into powder and mixed with a foaming agent, and sent through a kiln and softened. Bubbles form within the softened glass. When it cools, the material cracks and forms lightweight, coarse, foam-like aggregate pieces that can be used in various transportation construction projects.

Q. How did you learn of this material?

Foamed glass aggregate in use on the pilot project at Rt. 7 Wittpenn Bridge, Kearny

Aero Aggregates in Eddystone, Pennsylvania, reached out to the Department in 2018 to provide a technical presentation on foamed glass aggregate. An industry presentation is an established step in NJDOT’s process for exploring new technologies. If we are interested in the product, as we were in foamed glass aggregate, we start a pilot project.

Q.  When did NJDOT begin using foam glass aggregate?

Our pilot project was the Rt. 7 Wittpenn Bridge in Kearny, NJ in 2019. Use of this material replaced 32,000 cu.yds. of regular fill and saved almost 28 million bottles from the landfill. We used the material for a crossover from one side of the road to the other. We built it and let the contractor use the area for six weeks with heavy equipment traveling over it. We maintained survey equipment at the site and looked for settlement and any lateral spreading and nothing moved.

Q. What have been the most common uses?

For us at NJDOT, the most common uses have been as fill underneath roadways to raise the profile, behind existing abutments where we were putting in a new backwall and new girders and we wanted to lighten the lateral forces on the backwall, as backfill to the approach to a bridge, to resolve sheeting issues on a project, and as backfill behind a temporary wire wall.

Foamed glass aggregate placed behind an abutment on I-80 over Rockaway River, Denville

We have very soft, compressible soils beneath some of our roadways, and in areas of high tide or frequent flooding, therefore we want to raise the elevation of the roadway. Using heavy, natural fill material beneath the pavement box can lead to pavement that ultimately would ride like a roller coaster due to uneven settling.  A less costly approach is to over-excavate the existing soil and place with the foamed glass aggregate. At 22 lbs./cu.ft., the aggregate is buoyant, so regular weight soil is placed over it to weigh it down, and then the pavement box is built on top of the soil. Use of the aggregate lessens the amount of settlement and results in a nice smooth roadway.

Q.  Who are suppliers of this material?

Aero Aggregates is the supplier that we work with. They recycle glass from Pennsylvania and from a southern New Jersey recycling center. We appreciate that they are using local materials.

Q.  What are the environmental benefits of using this material? What is it replacing?

Foamed glass aggregate is saving millions of bottles from landfills. This material is made of 100 percent recycled material. In addition, the material replaces traditional backfill that would be quarried, and so minimizes depletion of natural resources. It also minimizes use of other material such as rebar, concrete and other foundation elements. In addition, it is lightweight, about half the weight of regular lightweight fill material, and so reduces transportation emissions. There are associated cost savings to its use.

Aggregate being applied behind wire wall on Fish House Road, Kearny

Q. Is there an ongoing assessment process for use of this material, or is it an established process?

We had questions in the beginning. The material was so light that we worried about its durability. The manufacturer provided results from testing and we tested the material in the field. Use of foamed glass aggregate is an established process at NJDOT. The material was first used in Germany in the 1980s, and in Norway in the 1990s to prevent rutting of pavements because it has good insulating qualities. It is useful in cold regions.

Q.  Are there limits to the transportation construction applications where this material can be used?

Foamed glass aggregate has its own compaction requirements; it is lightly compacted or graded out with lightweight equipment to avoid crushing of the aggregate. As mentioned above, it requires capping to weigh it down. Pavement design engineers want several inches of regular weight soil between the lightweight aggregate and the pavement box.

Q.   What is the state of industry knowledge and acceptance of the use of this material?

It is still early in the process of nationwide adoption. New Jersey is one of the first states to implement use of the material on our projects. We have received calls from many state DOTs asking how we began using it, and about our experience of using it in lieu of other lightweight material, so word is getting around. Aero Aggregates used it in Philadelphia around I-95. The industry is working on starting up new plants. Word is spreading through the contracting community. The first contractor that used it with us liked it so much they eliminated all other lightweight types of materials in the contract bid items. Through word of mouth, other design consultants and Contractors have picked up on use of the material.

Q.   Do you have current projects where this is being used and do you anticipate continued use of the material in the future?

View video on YouTube or access it from the NJDOT Platform

Yes, and we have some in design, and we will include foamed glass aggregate in the contract for future projects for consideration.

For future projects, we have not used foamed glass aggregate behind structural walls as yet, although we know it has been used in Philadelphia, and we are considering that application.

The Department is also considering applications related to temporary water storage in flood areas. Our current and past projects are using closed cell foamed glass aggregate, but an open cell aggregate is available. Its porosity might be beneficial in flood mitigation and other resiliency projects.

We really like the product and look forward to expanding its use. We are always looking for new technologies and this is one that will continue to be of great benefit.

Q.  What do you consider to be the keys to the successful adoption of the material?

Agency willingness has been the key to successful adoption of this innovative material.


Foamed Glass Aggregate [Video].  Retrieved at:

Foamed Glass Aggregate [Presentation].  Retrieved at:

From Landfill to Commitment to Communities Newsletter. How NJDOT Uses Non-Recyclable Materials for a Sustainable Future, Vol. 27, Spring 2023.  Retrieved at:

Research Spotlight: NJ Transit Grade Crossing Safety

A recently completed research study on NJ TRANSIT grade crossing safety focuses on identifying locations for rail grade crossing elimination. Researchers from Rutgers’ Center for Advanced Infrastructure and Transportation (CAIT), Asim Zaman, P.E., Xiang Liu, Ph.D., and Mohamed Jalayer, Ph.D., from Rowan University, developed a methodology using 20 criteria to narrow a list of 100 grade crossings to ensure appropriate identification for closure. The process helps NJ TRANSIT and New Jersey Department of Transportation (NJDOT) to direct limited funds to areas of greatest need to benefit the public.

Across the country, 34 percent of railroad incidents over the past ten years have occurred at grade crossings. The elimination of grade crossings can improve public safety, decrease financial burdens, and improve rail service to the public.

According to the proposed methodology, the 20 crossings recommended for closure located in Monmouth County (60%), Bergen County (25%), and Essex County (25%).

According to the proposed methodology, the 20 crossings recommended for closure located in Monmouth County (60%), Bergen County (25%), and Essex County (25%).

The researchers ranked grade crossings in New Jersey using the following data fields: crash history, average annual daily traffic, roadway speed, roadway lanes, length of the crossing’s street, weekday train traffic, train speed category, number of tracks, access to train platforms, intersection angle, distance to alternate crossings, distance to emergency and municipal buildings, whether emergency and municipal buildings are on the same street, and date of last or future planned signal and surface upgrades. This process resulted in a final list of 20 grade crossings eligible for elimination.

To understand how this study will be used, we conducted an interview with NJTRANSIT personnel Susan O’Donnell, Director, Business Analysis & Research, Ed Joscelyn, Chief Engineer – Signals, and Joseph Haddad, Chief Engineer, Right of Way & Support.

Q. How will the report inform decision-making? 

It is important to have solid research and strong evaluation criteria, such as developed by this study, on which to base decisions for grade crossing elimination. In addition to the study, we looked at what other state agencies and transit agencies have done with grade crossing elimination, as well as criteria recommendations from Federal Highway Administration (FHWA) and Federal Railroad Administration (FRA). Following up on this study, NJ TRANSIT and NJDOT are considering next steps that would be needed to close the 20 identified grade crossings. In New Jersey, the Commissioner of Transportation has plenary power over the closing of grade crossings.

Q. What other information will be needed to assess these locations? 

Local concerns about grade crossing elimination tend to focus on traffic re-routing, including the possible impacts on neighborhoods, time needed to reach destinations, and emergency vehicle access to all parts of a community. The criteria established by the study addressed these areas of concern. Prior studies have determined that the road networks around the identified locations are adequate to accommodate re-routed traffic. The current research study took into account the findings from those prior studies. As each project moves forward, NJDOT will determine if additional information will be needed.

Q. Is elimination of any of these grade crossings part of NJ TRANSIT’s capital program? 

All of the closings are part of the capital program. Funding for the grade crossing elimination comes from the federal government and NJ TRANSIT. NJ TRANSIT funding is in place to close the crossings.

Q. Are there benefits of the research study beyond identification of the 20 grade crossings?

The research study developed the criteria and process for identifying grade crossings for elimination. This framework can be used in the future to assess other grade crossings for possible elimination. NJ TRANSIT is grateful to NJDOT for funding this important research project to improve safety.

For more information on this research study, please see the resources section below.


Zamin, A., Alfaris, R., Li, W., Liu, Z. Jalayer, M., Hubbs, G., Hosseini, P., Calin, J.P., Patel., S. (2022). NJ Transit Grade Crossing Safety. [Final Report].  New Jersey Department of Transportation, Bureau of Research.  Retrieved from

Liu, Z., Jalayer, M., and Zamin, A. (2022). NJ Transit Grade Crossing Safety. [Technical Brief]. New Jersey Department of Transportation, Bureau of Research.  Retrieved from

Innovation Spotlight: NJDOT Local Aid Design Assistance Program

When cities, counties, and other local public agencies (LPAs) use Federal funds for transportation projects, they must follow all of the applicable Federal laws and regulations attached to the Federal aid. NJDOT, like other state departments of transportation (DOTs), oversees the LPA program and works with agencies to help them use Federal-aid effectively. During Round 2 of the Every Day Counts Program (EDC-2), FHWA promoted innovative strategies for overcoming common challenges with Locally Administered Federal-Aid Projects including practices for enabling “Consultant Services Flexibilities” on local programs and projects.   

To aid its LPAs in the delivery of its non-traditional projects programs, the NJDOT Division of Local Aid and Economic Development (Local Aid) established the Local Aid Design Assistance Program. The Design Assistance Program seeks to support LPAs that have received federal grants through the Safe Routes to School and Transportation Alternatives Set-Aside (TA Set-Aside) programs. The Program provides a pool of pre-qualified engineering design consultants to assist LPAs with plans, specifications and estimates (PS&Es) with the goal of seeing more infrastructure projects implemented. Laine Rankin, Director of Local Aid and Economic Development, and Julie Seaman, Project Management Specialist, described the program.

The NJDOT Local Aid Resource Center website provides links to information on the Design Assistance Program

The NJDOT Local Aid Resource Center website provides links to information on the Design Assistance Program

What are some of the most common challenges local agencies face with the project design process?

LPAs often face lack of staff, lack of funding, and staff turnover, all of which can limit their capacity to take on the federal grant process and can result in delays in infrastructure project planning and implementation. Because New Jersey is a home-rule state, the State has limited jurisdiction over county or local roads. Instead, the municipalities and counties are responsible for infrastructure improvements on their roads. The NJDOT Local Aid Office assists the municipalities in implementing these projects by administering the federal funding for them. Local Aid is ultimately responsible for the spending of these federal dollars.

Safe Routes and TA Set-Aside grant recipients face challenges in understanding and complying with requirements related to federal grant administration. In particular, the requirements of the Brooks Act, also known as Qualifications Based Selection, prove difficult to satisfy in project administration. The Brooks Act details federal requirements for the procurement of professional services of consultants, including:

  • Issuing a request for proposal or RFP from consultants based on approved written procurement policies and procedures
  • Solicitation, evaluation, ranking and selection of consultants
  • Selecting a consultant based on qualifications and experience, not cost
  • Negotiating a fair and reasonable cost and contract terms with selected consultant
  • Monitoring the consultants’ work
  • Evaluating the consultants’ performance
  • Contract completion

How does the design assistance program work?

The federal grant process

The federal grant process

Most grant applications that Local Aid receives do not describe projects that are construction-ready. LPAs need assistance to complete designs, and develop engineering plans, specifications, and estimates required to see a project built.

Through the Design Assistance Program, NJDOT procures a pool of design consultants that LPAs can then choose to work with. Once NJDOT and the MPOs have chosen the projects that will be funded for a grant cycle, Local Aid develops a Request for Proposals (RFP) that lists the selected projects and scope for each grant. The NJDOT Office of Procurement solicits a pool of engineering firms that will be able to assist the grant recipients with their particular projects. The firms considered for the pool are typically familiar with requirements associated with developing a set of plans which are compliant to the NJDOT plan and AASHTO standards. Once the consultant pool has been approved by NJDOT management, a letter is sent to all of the grant recipients of that grant cycle informing them of the engineering firms available.

The NJDOT Local Aid Office partners with NJ’s three Metropolitan Planning Organizations in the TA Set-Aside project selection process

The NJDOT Local Aid Office partners with NJ’s three Metropolitan Planning Organizations in the TA Set-Aside project selection process

Funding for design assistance comes from the same line of federal funding as the SRTS grant and the TA Set-Aside grants. LPAs receive grant funds for the design program above the amount awarded for the project itself.

For how many years has the design assistance program been operating?

Although this is a pilot program, we initiated the process in April of 2014 and it took about a year and a half to get it up and running following meetings with FHWA, NJDOT Procurement, and the NJDOT Deputy Attorney General. Our office talked to peers in other states including Kentucky, New York, Missouri, among others to understand how other Local Aid offices were handling design assistance for grant recipients and the consultant solicitation process. Design assistance programs were developed for both the Safe Routes to School (SRTS) and the Transportation Alternatives Set-Aside (TA Set-Aside) programs. Design assistance first became available to grant recipients in the 2014 grant round and we solicit grant applications on a two-year cycle, or after a grant solicitation for that particular program has been completed.

How do the LPAs find out about the design assistance program?

TA Set-Aside Grant Webinar explained the purpose and benefits of the Local Aid Design Assistance program

TA Set-Aside Grant Webinar explained the purpose and benefits of the Local Aid Design Assistance program

The design assistance program is introduced in our general training session for applicants that describes how to apply for a Safe Routes or TA Set-Aside grant. After the grant awards are announced, information about the program is included in the letter that we send to grant recipients, and a separate informational session is held with grant recipients to discuss the design assistance pool. All grant recipients are eligible to take part in the program; they do not apply for the program and there is no obligation to take part.

Can you say what percentage of grant recipients choose to use the program?

It has taken some time to publicize the program, but awareness among LPAs is growing.  In 2016, 19 of 36 TA Set Aside grant recipients, and 12 of 17 SRTS grant recipients elected to use the program.  Our 2018 pools are still open; to date, 13 of 25 TA Set Aside grant recipients and 13 of 18 SRTS grant recipients have shown interest in the program. We have approval from FHWA to keep the pool open for a year, with an option to extend up to two years. If an LPA proposes a TA Set-Aside project that involves some specialized work that the engineering firms could not respond to – such as architectural design, then the LPA will not be able to use the design assistance program.

Do NJDOT, the LPA, and the consultants work together through the design assistance process?

Yes. The project application is reviewed and a field meeting is typically scheduled with representatives of the LPA, the consultant engineering firm, the Local Aid regional office, and NJDOT environmental staff. The LPA, NJDOT, and the consultant then work together to develop the scope of work. The consultant prepares a fee proposal and Local Aid develops an independent cost estimate that is used to compare with the consultant’s proposal. NJDOT assists in negotiating the agreement between the LPA and the consultant but the LPA executes an agreement directly with the consultant. NJDOT authorizes federal-aid funds for the design, in excess of the project grant award. The LPA continues to work with the Local Aid District Office through the design process, and NJDOT conducts an environmental review as well. Before the project goes to construction, the plans and specs are submitted to the Local Aid District office for approval in order to ensure a biddable, buildable, project. The LPA pays the consultant directly and then requests reimbursement for the cost from NJDOT.

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What benefits have you seen from the program?

In our experience, what may seem like a simple project, such as installing a sidewalk, can be very complicated. In many cases, particularly for Safe Routes projects, the design costs may exceed the construction costs. We provide design funds for LPAs that choose to procure an engineering firm, but the LPA must comply with the Brooks Act in their procurement process. Some LPAs choose to work with their municipal engineer, but the engineer must be qualified to do the work. Municipal engineers who are involved in the design of these projects are not allowed to also inspect the projects, and these inspection costs increase the overall project cost for the LPAs. For LPAs not using in-house engineering services, the design services procurement process is burdensome.

Through the Local Aid Design Assistance Program, we are distributing more federal funds and seeing more projects advancing than in the past. When we give a grant out, we want folks to build it. LPAs can develop more involved projects. The program results in better compliance with complex state and federal regulations and helps resolve typical engineering issues, such as right-of-way and utilities, that can affect project cost and schedule. LPAs are better prepared for the permitting process.

Do you see the program continuing into the future?

We will be continuing the program. There are always some tweaks to be made but the program is helping local agencies implement projects that improve health and safety throughout the State.


American Council of Engineering Companies (ACEC). (u.d.). The Brooks Act: Federal Government Selection of Architects and Engineers. Public Law 92-582, 92nd Congress, H.R. 12807, October 27, 1972. Legislation on Website. Retrieved from:

American Council of Engineering Companies (ACEC). (u.d.). The Brooks Act: How to use Qualifications Based Selection. Website. Retrieved from:

FHWA. (u.d.). EDC-2 Innovations. Website. Retrieved from:

NJDOT. (2020). Applying for Federal Transportation Alternatives Set-Aside Program Funds Webinar TA Set-Aside Grant Webinar Session #2. Online Session. Retrieved from:

NJDOT. (2020). Transportation Alternatives Set-Aside Design Assistance Program. Presentation. Retrieved from: