Evaluation of Precast Concrete Pavement Systems Webinar

Join the NJDOT Bureau of Research on June 10th for a Lunchtime Tech Talk! Webinar on Evaluation of Precast Concrete Pavement Systems: Identify Existing Precast Concrete Pavement Systems and State Specifications

Faculty and research staff members from the Rowan University CREATEs program, Dr. Yusuf Mehta and Dr. Daniel Offenbacker, will discuss the results of a research study performed for NJDOT.

Rigid pavements play an important role in highway infrastructure, primarily in regions with high traffic density such as New Jersey. NJDOT is continuously exploring innovative pavement rehabilitation strategies, such as Precast Concrete Pavement (PCP), that allow for faster and more durable rehabilitation of rigid pavements. NJDOT initiated a research study with Rowan University CREATEs to identify, evaluate, and compare precast pavement systems, specifications, and practices currently in use. The study included an extensive literature review and surveys with Subject Matter Experts from various state DOTs that have experience with precast pavement rehabilitations.

The presenters will discuss the types of precast pavement systems, past construction experiences, and overall recommendations for precast pavements. Specifically, they will discuss previous studies and experiences using precast pavements, different quality control specifications, and recommendations for future implementation in NJ. They will also speak on the development of an overall approval process for considering the use of newly-developed precast pavements in NJ.

The event is free, but registration is required to receive the URL link to the webinar.  NJ PE credits are available, but you must be registered for the event. Click through the link below to register for this webinar event:

Evaluation of Precast Concrete Pavement Systems: Identify Existing Precast Concrete Pavement Systems and State Specifications
Date: Wednesday, June 10, 2020
Time: 12:00 – 1:15 PM

Share Your Ideas on the NJ Transportation Research Ideas Collaboration Site!

The New Jersey Department of Transportation’s (NJDOT) Bureau of Research invites you to participate in the NJ Transportation Research Ideas Collaboration site.

We are asking NJDOT’s research customers and other transportation stakeholders to propose research ideas for the NJDOT Research Program. Join us in finding workable solutions to problems that affect the safety, accessibility, and mobility of New Jersey’s residents, workers, visitors and businesses.

REGISTER TO PARTICIPATE.  Once you are registered, you may submit ideas at any time.  If you registered last year, you do not need to register again.

HOW DO I SUBMIT AN IDEA?  Only registered participants can log in to submit a new idea or vote on other ideas to show your support. Register at the NJ Transportation Research Ideas website welcome page here:  https://njdottechtransfer.ideascale.com/

NEXT ROUND OF RESEARCH.  Please submit your research ideas no later than December 31, 2019 for the next round of research RFPs. The NJDOT Research Oversight Committee (ROC) will prioritize research ideas after this date, and high priority research needs will be posted for proposals.

Questions about how to register?
Email: ideas@njdottechtransfer.net

For more information about NJDOT Bureau of Research, visit our website:  http://www.state.nj.us/transportation/refdata/research/

Or contact us:  Bureau.Research@dot.nj.gov or (609) 963-2224.

Spotlight: New Technology Evaluations

The New Technologies and Products (NTP) Unit in NJDOT’s Division of Bridge Engineering and Infrastructure Management reviews and evaluates new technologies and products submitted by manufacturers, vendors and suppliers. The unit is currently evaluating over 50 products for possible use at NJDOT to address needs related to safety, pavement, drainage, bridges and structures, among other categories.

NJDOT defines a new technology as “any product, process, or material used in the construction and maintenance of roadways and bridges that is not covered by existing NJDOT standard specifications or construction details, thereby requiring a formal evaluation for approval.” Products may receive a formal evaluation if they are finished and marketed, and address high priority needs.

The unit maintains the New Technologies and Products database of tested products from 2002 to the present. The database displays the category, the name of the product with a link to the product webpage, the company and the status of the evaluation. The NTP database status code legend is available on the NJDOT New Technology Evaluations webpage. Products may be actively undergoing testing, in a demonstration phase, or specification development phase, or in other stages of evaluation.

If, through the evaluation process, a technology or product is found acceptable for use on NJDOT projects, development and implementation of a standard specification, construction detail, or design guideline is still needed through a baseline document change.

Evaluation typically takes two to three years, although technical information and testing data from other testing agencies may expedite the process. Proposals for use of a new technology on a specific project, and recurrent use of an alternate or non-standard item on several projects, can lead to acceptance as a standard item.



Evaluating New Jersey’s Use of Raised Pavement Markers for Roadway Safety

In the United States, data has shown that more than a third of fatal crashes on two-lane undivided highways and 27 percent of fatal crashes on four-lane divided highways occur in dark, unlighted conditions. Raised Pavement Markers (RPMs) are a common device deployed for roadway safety around the world since the 1930s. RPMs are delineation devices used to improve preview distances and provide guidance for drivers in inclement weather and low-light conditions. There are two main types of RPMs, ones that can be used with snow plows and ones that cannot.

While most states install RPMs selectively based on particular locational characteristics of the roadways, New Jersey uses RPMs along all centerlines (solid and skip), regardless of traffic volume, roadway geometry, or roadway classification. The extensive use of RPMs in New Jersey has raised interest in understanding 1) whether this significant investment generates variant safety benefits at different locations; 2) whether there are alternatives or modifications to the existing RPMs; and 3) how to optimize the installation, monitoring, and maintenance of RPMs and their promising alternatives in order to attain a more cost-effective safety improvement.

The selected team from Rutgers University and Rensselaer Polytechnic Institute employed four distinct methods to address these research questions. The first was to conduct a literature review to inform the development of a methodological framework for quantifying the safety and cost-effectiveness of RPMs and their alternatives, based on specific road and traffic characteristics. Second, the researchers developed a luminance measurement method to compare the luminance of RPMs to different markers’ ability to inform drivers of road lines. Luminance measurement is defined as “the amount of visible light leaving a point on a surface in a given direction” (“Lighting Design Glossary”). Third, the group conducted a survey of other state DOTs practices and their guidelines for installation, including alternatives used. Lastly, the researchers developed a computer-aided decision support tool to calculate the life cycle costs of RPMs and their alternatives. Different alternatives were considered throughout the study, including various forms of rumble strips, preformed tape, and delineators.

The researchers came to several findings that provided insight into NJDOT’s current use and potential future research opportunities. The literature review of previous studies was inconclusive, with no consensus on whether RPMs affect the crash rate on roadways, with past research showing both negative and positive safety changes post-installation.

RPM samples used for measurements in the luminance tests. Photo Source: Xiang et al.

The survey of state DOTs yielded 22 responses from states throughout all regions of the country. The survey had two main sections, “RPM Installation” and “RPM Inspection and Maintenance”. No consensus or clear pattern was found among the states in terms of practices for installation, inspection, maintenance, and alternatives used. However, the researchers found that other state DOTs were more selective than New Jersey in choosing RPM installation sites based on traffic volume, accident history, and weather conditions.

To quantify the contribution that RPMs make towards safety outcomes on New Jersey roads, researchers compared the safety performance of county roads since unlike state roads, some county roads do not have RPMs installed. The researchers found that county roads with RPMs had a 19 percent lower crash rate than county roads without RPMs. The most significant decreases in crash rates occurred in nighttime, wet weather conditions, providing insight into the conditions that RPMs may be most effective.

In the lab luminance study, the team tested samples of new and used RPMs, along with alternatives such as wet pavement reflective tape and channel-mounted delineators to determine how far away drivers could see the markers in nighttime conditions. The average lifecycle for RPMs is 6 years, with a maintenance cycle of 2-3 years. Used RPMs showed a 20-30 percent decrease in luminance than new RPMs, but that did not translate to decreased visual performance.

Finally, the team created a computer-aided decision support tool to evaluate and compare the life cycle cost of RPMs and alternatives, based on specific operational characteristics. Decision-makers can couple information on safety benefits for each device with the total cost for per unit crash reduction from the tool to compare the value of the investment. The tool accounts for installation cost, traffic control cost, traffic delay cost, inspection cost, maintenance and repair cost, as well as the liability cost associated with incidents due to damaged RPMs or alternatives.

The research team also suggested several areas for future study for advancing NJDOT’s understanding of RPMs and their alternatives. The researchers recommended a study of optimal spacing or degree of continuous delineation that drivers need for safety. In the luminance study, all the devices had high visual performance despite variance in luminance when tested at a 100-meter viewing distance. However, the researchers noted, additional study was needed to see how the differences in luminance could affect visual performance at the threshold visibility distance (when the devices can be first seen). The results could help identify which device gives drivers more time and distance, resulting in potential reduction in nighttime crashes.

Rumble Strips. Photo Source: FHWA.

Lastly, one of the alternatives frequently mentioned throughout the study is rumble strips, which are used on roadways to create a noise and vibration to alert a driver when they leave their lane. When painted with retroflective coating to increase visibility, they are called rumble stripes (FHWA 2019). The researchers explained that rumble strips have not been studied in regard to safety effectiveness in New Jersey due to data limitations, making it a potential future research area.

New Jersey is in a unique position compared to other states with its comprehensive use of RPMs on state roadways. The researchers were able to provide valuable information to NJDOT, including a methodological framework for the department moving forward to quantify the safety effectiveness of RPMs and their alternatives and a computer-aided decision support tool to estimate life cycle cost. With this information and targeted areas for future research, NJDOT can aim to make cost-effective investments that will improve roadway safety.


FHWA. “Rumble Strips and Rumble Stripes.” FHWA. April 1, 2019. https://safety.fhwa.dot.gov/roadway_dept/pavement/rumble_strips/general-information.cfm.

“Lighting Design Glossary.” Lighting Design and Simulation Knowledgebase. https://www.schorsch.com/en/kbase/glossary/luminance.html.

Liu, Xiang, John Bullough, Liwen Tian, Shan Jiang, and Mohsen Jafari. Evaluation of Raised Pavement Markers, Final Report. July 2018.

Liu, Xiang, John Bullough, Liwen Tian, Shan Jiang, and Mohsen Jafari. “Technical Brief: Evaluation of Raised Pavement Markers.” July 2018.


New Protocol for Accepting Over-Coating Paint on Steel

The Research Advisory Committee of the American Association of State Highway and Transportation Officials (AASHTO) selected an NJDOT project as one of 16 high-value research projects for 2019 in the category of Smart Maintenance and Preservation. Researchers from Rutgers’ Center for Advanced Infrastructure and Transportation, Perumalsamy Balaguru, Husam Najm, and David Caronia, developed a new testing method for the durability of paint overcoat on steel structures, such as bridges.

NJDOT received AASHTO’s Research “Sweet Sixteen” 2019 award for innovative research establishing a new protocol for durability testing of structural steel overcoats.

On behalf of the NJDOT Bureau of Research, Giri Venkiteela, Research Project Manager, delivered a poster presentation and Pragna Shah, Research Project Manager, accepted the AASHTO award at the 2019 National RAC and TRB State Representatives Meeting in Santa Fe, New Mexico in July 2019.

The new protocol allows for reduced testing time from previous methods, identifies durable coatings, simulates field performance, and has significant potential for adoption in accepting all new coatings. This new protocol will save money and reduce environmental pollution resulting from degraded coatings.  The innovative research for this new protocol is described in the Final Report and Technical Brief.

Local Access Management Regulations

The New Jersey Department of Transportation (NJDOT) is responsible for administering an access management policy for the state highway system.  The Federal Highway Administration (FHWA) defines access management as “the proactive management of vehicular access points to land parcels adjacent to all manner of roadways. Good access management promotes safe and efficient use of the transportation network.”

Figure 1: Conceptual Roadway Functional Hierarchy. Source: FHWA, 2017

Key components of an access management code include access spacing, driveway spacing, safe turning lanes, median treatments, and right-of-way management. While New Jersey’s access management code is highly regarded, it only applies to state highways and not local roads. Local authorities in New Jersey do not have uniform access management codes, regulations, or standards for local roads. This creates a gap in policy for how to address the issues that arise when new developments take place on local roads near intersections with state routes or when state highway improvements are required near intersections with local roads.

To address these issues, the NJDOT Bureau of Research solicited a research study of local access management regulations. The primary research objective was to identify and recommend strategies, tools, and guidelines to facilitate access management on local roads (i.e., county and municipal) intersecting and/or impacting state highways in New Jersey.

The selected research team sought to evaluate how other state DOTs address access management on local roads near state highways and explore how New Jersey local government and transportation agency officials perceive these access management issues between state and local jurisdictions

The research team carried out several tasks. First, they compiled a literature review of local access management drawing upon resources from state DOTs, the FHWA, the Transportation Research Board (TRB), local governments, among others (see Figures 1 and 2). Next, they organized and facilitated discussions with a stakeholder committee of professionals in New Jersey (e.g., municipal, county, and MPO engineers and planners) with experience addressing access management. The team conducted structured interviews with state DOTs from 13 different states, including California, Colorado, Virginia, and Pennsylvania.  NJ local government officials were reached through an online survey to gather information on current practices, issues, and relevant case studies. The researchers conducted case study analyses of specific problematic issues at intersections of local roads and state highways in New Jersey. Four site locations were selected based on the availability of data, severity of issues, geographic and land use patterns, and the relative difficulty for access management implementation based on the current system.

The interviews with other state DOTs focused on several themes, including the basis and scope of authority given under current access management laws and regulations; issues related to the development of corner lots; proactive steps taken to avoid access management issues; and recommendations for developing and implementing access. From the interviews with the state DOT officials, the research team gleaned that there is substantial variation on access management approaches. Similar to New Jersey, other State DOTs are mostly focused on

Figure 2: Diagram of Intersection Corner Clearances. Source: TRB, Access Management Manual, 2014.

state highways, although many acknowledged facing local-road issues. The team uncovered some best practice strategies that could be pertinent to New Jersey, including the development of corridor agreements between local governments and state DOTs; training local government professionals on access management; establishing communication channels between local offices of state DOTs and local governments; and funding local governments to develop their own access management guidelines and standards.

Stakeholder meetings and surveys of local New Jersey officials revealed broad support for advancing local access management guidelines. Among those surveyed, 27 percent said the local agencies that they served had formal or informal access management guidelines and 60 percent said local access management standards similar to the state highway code would be beneficial. However, key barriers were also identified, including the cost and availability of training. Local officials generally were not in favor of extending NJDOT’s authority beyond the State Highway System to county and local roads, and preferred initiatives from NJDOT to local governments that involved dedicated funding, improved coordination or dialogue, or technical assistance.

Based on the literature review and survey feedback, the research team offered for consideration to NJDOT and local governments some criteria for intersections between state highways and local roads where no local access code or guidelines are available (see Table 1).

The research team also recommended that NJDOT:

  • Develop project-specific access management criteria for intersections between state and local roads in highway improvement projects, which will work to communicate early to local agencies and property owners if they may lose parking, road access, right-of-way, etc.
  • Provide assistance via funding and training to encourage local governments to develop their own access management guidelines consistent with state code yet with more flexibility to their local roads.
  • Provide incentives for local governments to establish and apply access management policies and guidelines (using a similar approach that has been used to encourage Complete Streets policy adoption and implementation training).
  • Adopt proactive measures such as corridor agreements with local governments at corridors with highway improvement projects in the next 5 or 10 years according to the state highway improvement plan of local MPOs and NJDOT and specify the spacing criteria for intersections between state and local roads on selected corridors.
  • Establish communication channels between divisional offices of NJDOT and local governments so that all parties are aware of projects early on.
  • Continue working with the stakeholder committee established for the research study to foster dialogue between NJDOT and local governments on access management

Table 1Criteria of Access Spacing and Corner Clearance based on Posted Speed Limit

Criteria Agency Posted Speed Limit (mph)
25 30 35 40 45 50 55
Minimum Access Spacing Peer State DOTs Minimum Access Separation (feet)
NJDOT(C) 105 125 150 185 230 275 330
Peer State DOTs 125-245 125-245 125-250 245-305 245-440 440-660 440-660
AASHTO Sight Distance















TRB-Manual** 330 330 330 330 660 660 880
NJ Local Agencies 150-300 200-350 250-425 300-475 350-525 400-600 400-600
Minimum Corner Clearance Minimum Distance from Corner (feet)
NJDOT(C) 50 50 100 100 100 100 100
Peer DOTs Same as Access Spacing
NJ Survey

Same as Access Spacing

Notes: (C) stands for Code/Regulations/Ordinance; (G) Stands for Guidelines/Manual/Standards; * for right-turn-only access points with median blockage; ** TRB Access Management Manual.

The research team also suggested some future work items to further advance implementation. Notably, the development of semi-automated screening tools and GIS overlays could assist in the identification of problematic locations based on state or local intersection spacing criteria. This could help expedite the design process and facilitate proactive communications and problem solving between NJDOT and local governments. Additionally, NJDOT could establish a co-training program for their related departments and local agencies to deliver needed training on general knowledge, prevailing standards and design concepts, institutional procedures, and real-world practice on past state and local access management projects. Based on this report, there is clear evidence of strong support across local and state officials as NJDOT looks to implement these recommendations and further study how to improve current practices.

FHWA. “What Is Access Management?” February 15, 2017. https://ops.fhwa.dot.gov/access_mgmt/what_is_accsmgmt.htm

Jin, Peter J., Devajyoti Deka, and Mohammad Jalayer. “Local Access Management Regulations – Technical Brief.” 2019. FHWA-NJ-2018-003 TB

Jin, Peter J., Devajyoti Deka, and Mohammad Jalayer. “Local Access Management Regulations – Final Report.” 2019. FHWA-NJ-2018-003

Williams, Kristine M., Vergil G. Stover, Karen K. Dixon, and Philip Demosthenes. Access management manual. 2014. https://trid.trb.org/view/1341995

Quantifying Greenhouse Gas Emissions of Asphalt Pavement Preservation at Construction and Use Stages Using Life Cycle Assessment

Employing pavement preservation techniques can help reduce greenhouse gas emissions, and contribute to savings for both transportation agencies and drivers, according to a recently published study in the International Journal of Sustainable Transportation. The researchers determined that extending the life of pavement through preventive maintenance  can reduce greenhouse gases by 2 percent; save transportation agencies between 10 to 30 percent in spending; and reduce cost for drivers between 2 to 5 percent on fuel consumption, tire wear, vehicle repair, and maintenance because of smoother surfaces (Bates 2019). This research can assist transportation agencies like NJDOT and local public agencies consider the right maintenance strategies when determining environmental effects in future projects.

This research is notable, in part, because pavement preservation has been a hot topic among many state highway agencies.  The Federal Highway Administration’s Every Day Counts (EDC) program brought greater attention to the benefits of pavement preservation by making it one of its national initiatives in the fourth round of the EDC program. Through EDC-4, many states made commitments to increase their use of pavement preservation treatments and give a fuller commitment to its integration in their maintenance programs (FHWA 2018a).

NJDOT has significantly increased its use of preventive maintenance treatments on roadways in good or fair condition in recent years. Applying preventive maintenance treatments early has proven to be cost-effective by slowing the rate of deterioration and allowing NJDOT to reduce the backlog of deficient pavements.  The lead author  for this research, Hao Wang, previously worked as the co-investigator on a NJDOT-funded research study, Appropriate Implementation of Pavement Preservation Treatments, completed in 2015. That study looked at the pavement preservation techniques that NJDOT could use on its high volume state-maintained roads (Wang & Vitillo 2015).

Pavement preservation consists of surface refreshment to alleviate functional indicators of deterioration, such as friction, minor cracking, or oxidation. The three pavement preservation treatments considered in this recently published research were thin asphalt overlay (placing up to 2 inches of asphalt on roads), chip seal (spraying asphalt emulsion on pavement and laying aggregate), and crack seal (filling cracks with rubberized asphalt or polymer-modified asphalt with some filler).

While previous studies have looked at the environmental impact of preservation treatments at the construction stage, few have considered how the change in pavement smoothness affects vehicle fuel consumption and tailpipe emissions. The purpose of this study was therefore to systematically look at both the construction and use stage to determine the environmental impacts of several pavement preservation treatments throughout the whole life-cycle.

In order to quantify the environmental impact, the researchers used life-cycle assessment (LCA), focusing specifically on CO2 emission for global warming potential (GWP). To determine the emissions during construction stage, the group looked at the raw material, manufacturing, transport, and placement.

Illustration of different stages in pavement LCA with system boundary (Wang et  al. 2019)

Researchers measured pavement condition using the International Roughness Index (IRI), which states are required to report to the FHWA as it provides a standardized and objective measurement methodology. IRI models for pre- and post-treatment were then created with data obtained from the Long-Term Pavement Performance (LTTP) program Specific Pavement Studies (SPS-3). The LTTP program was established in 1986, and has been maintained by the FHWA since 1991, with the purpose of collecting and storing pavement performance data in a centralized database (FHWA 2019). SPS-3: Preventive Maintenance Effectiveness of Flexible Pavements specifically compares the effectiveness and mechanisms of selected maintenance treatments to preserve and extend pavement service life, safety, and ride quality (FHWA 2018).

The pavement’s pre- and post-treatment effects on vehicle fuel consumption and air quality were then analyzed using data from the Highway Development and Management Tool (HDM-4) and the Motor Vehicle Emission Simulator (MOVES). HDM-4 is a software package that is used worldwide for analysis, planning, management, and appraisal of road maintenance, improvements, and investment decisions. MOVES is the EPA’s emission modeling system for mobile sources, which is used at all project levels to estimate for criteria air pollutants, greenhouse gases, and air toxics.

The results for the CO2 emissions at the construction stage showed significant differences in energy consumption for the three pavement preservation treatments, mostly due to the varying raw materials and manufacturing processes. Thin asphalt overlay had the highest energy consumption, followed by chip seal, and then crack seal, which requires a comparatively small amount of material over the entire process. Additionally, thin asphalt overlay tends to have a higher cost compared to the other two. At the use stage though, thin overlay showed the highest reduction of CO2 emissions, based on the post-treatment IRI values, and crack seal the lowest reduction.

A machine compacts asphalt over existing pavement at a construction site at John F. Kennedy International Airport in New York City (Wang 2019).

Despite their environmental impacts, the various preservation treatments still had an overall benefit when quantified using a life-cycle assessment approach, according to the researchers. Additionally, they found that the timing of preservation treatment could have a large effect on the subsequent emissions at the use stage. Specifically, for thin overlay and chip seal, the optimal time to achieve maximum life-cycle environmental benefit becomes earlier as traffic volume or initial IRI value increases. Despite the variance in effectiveness over the life-cycle, all three treatments reduced emissions overall.

In explaining the rationale for the research, the study’s authors  note that transportation sector is second to electricity in generating greenhouse gas emissions among all U.S. end-use sectors at 27 percent. Additionally, fuel consumption of vehicles accounted for 83 percent of the total greenhouse gas emissions within the transportation sector in 2015. In December 2018, Governor Phil Murphy announced that New Jersey would be rejoining the Regional Greenhouse Gas Initiative, a group of neighboring states that have set policy goals and initiatives in order to achieve a 100-percent clean-energy portfolio by 2050 (Murphy 2018). Improving the performance of existing highways is well-aligned with this initiative.

By filling the gap in research focused on  the entire life-cycle environmental impacts of pavement preservation treatments, the research offers important information for life-cycle assessment in future roadway projects. As transportation agencies look at how to manage their current assets, reduce costs, and avoid and minimize environmental impacts, pavement preservation offers a multitude of benefits to help achieve these goals.

Shown above is a Bergkamp M1, which can be used for slurry seal and microsurfacing. Source: By Eric Pulley – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5176467


Bates, Todd. “Keeping Roads in Good Shape Reduces Greenhouse Gas Emissions, Rutgers-Led Study Finds.” Rutgers Today. January 14, 2019. https://news.rutgers.edu/keeping-roads-good-shape-reduces-greenhouse-gas-emissions-rutgers-led-study-finds/20190114#.XH2SRYhKiUl.

BTS. “Road Condition.” Bureau of Transportation Statistics. June 2015. https://www.bts.gov/content/road-condition.

FHWA. “Long-Term Pavement Performance.” FHWA. 2019. https://highways.dot.gov/long-term-infrastructure-performance/ltpp/long-term-pavement-performance.

FHWA. “Pavement Preservation (When, Where, and How).” Center for Accelerating Innovation. May 30, 2018a. https://www.fhwa.dot.gov/innovation/everydaycounts/edc_4/pavement.cfm.

FHWA. “Specific Pavement Studies.” FHWA. March 12, 2018b. https://highways.dot.gov/long-term-pavement-performance/data-collection/specific-pavement-studies.

Murphy, Phil. “Murphy Administration Proposes Rules For State’s Re-Entry Into Regional Greenhouse Gas Initiative.” Office of the Governor. December 17, 2018. https://nj.gov/governor/news/news/562018/approved/20181217b.shtml.

Vitillo, Nicholas, and Hao Wang. “Appropriate Implementation of Pavement Preservation Treatments.” NJDOT. April 2015. https://www.state.nj.us/transportation/refdata/research/reports/FHWA-NJ-2015-011-I.pdf.

Wang, Hao, Israa Al-Saadi, Pan Lu, and Abbas Jasim. “Quantifying Greenhouse Gas Emission of Asphalt Pavement Preservation at Construction and Use Stages Using Life-cycle Assessment.” International Journal of Sustainable Transportation. January 11, 2019. https://www.tandfonline.com/doi/abs/10.1080/15568318.2018.1519086?journalCode=ujst20.

The Use of Porous Concrete for Sidewalks

In December 2017, a team of researchers at the Center for Advanced Infrastructure and Transportation (CAIT) at Rutgers University published a research study for NJDOT on “The Use of Porous Concrete for Sidewalks.” A porous concrete sidewalk typically consists of a porous concrete slab on top of an open graded stone reservoir layer. A filter fabric is placed between the underlying soil and the reservoir layer. One of the most important benefits of porous concrete is its effectiveness for stormwater management, i.e. improving water runoff quality, reducing stormwater runoff, and restoring groundwater supplies. However, there are concerns related to its construction, cost, maintenance, and durability.

Rodding and finishing of a porous slab. Photo source: Najm, 2017.

The primary objective of the research study was to evaluate the various factors that influence the performance of porous concrete in sidewalks. These include hydraulic performance to meet New Jersey Department of Environmental Protection (NJDEP) regulations and structural performance to meet typical sidewalk strength requirements as well as life-cycle cost and maintenance requirements. The researchers compared the performance of porous concrete in sidewalks with other materials, such as conventional concrete and asphalt alternatives, and tested various pervious concrete mixes to evaluate the hydrological and structural performance and energy budget versus conventional concrete mixes. The team also conducted a cost benefit analysis for use of porous concrete on sidewalks versus alternatives. The study resulted in recommendations and guidelines that NJDOT could use to inform the mitigation of stormwater runoff and development of maintenance standards.

The study found that the effectiveness of porous concrete in reducing stormwater runoff could contribute to cost savings. The research report examined a number of important considerations affecting the broader implementation of this technology. A life-cycle cost analysis of three sidewalk design alternatives—porous concrete, porous asphalt, and conventional concrete—found that porous concrete had the highest initial construction cost, with conventional concrete coming in slightly less, and porous asphalt being the cheapest. The study showed that the service life of porous concrete may be shorter than conventional concrete, driving up the life-cycle cost and potentially offsetting the savings from stormwater management best practices. For porous asphalt, which has the shortest service life, findings showed that if the service life ratio of porous asphalt compared to conventional concrete was greater than 0.60, then porous asphalt would be the most economically competitive option of the three. Another consideration in some areas is that it may be less effective to implement porous pavement if the soil has low permeability. The report notes that, once implemented, periodic maintenance is required to prevent clogging from debris and sediments, and freezing in the winter to avoid failure due to freeze and thaw cycles.

Porous concrete beam during flexural test. Photo source: Najm, 2017

The research team recommended that next steps should include construction of a porous concrete sidewalk and a porous asphalt sidewalk for long- and short-term performance testing. They noted that implementation should include geotechnical evaluation of the subsoil layers for infiltration rates, hydraulic design and storm-runoff analysis, selection of porous mix design based on NJDOT specifications and contractor recommendations, sample prisms and cylinders extracted for lab tests, scheduled maintenance based on NJDEP and NJDOT guidelines, and regular inspection. While there are environmental benefits to the implementation, such as filtration of contaminants like metals, oils and grease, to improve water quality and reduce chloride pollution, there are also concerns it can cause groundwater contamination. These concerns, along with recommended further performance testing, highlight the importance of interim steps before wider implementation.

Pervious pavement is a key component of green infrastructure methods that seek to improve stormwater management. The New Jersey Department of Environmental Protection lists the practice among others such as rain barrels, cisterns, and rain gardens/bioretention basins as strategies that can be implemented on a variety of scales in order to both treat runoff and reduce runoff volume. Yet, as the report notes, there has been little published research on performance and practical experience in the United States, highlighting the researchers’ final recommendation for further testing.


Green Infrastructure in New Jersey. (2018). Retrieved from https://www.nj.gov/dep/gi/More_Info.html

Najm, H., Wang, H., Miskewitz, R., Roda, A. M., Ali, A., He, H., Chen, X., Hencken, J. (2017). The Use of Porous Concrete for Sidewalks. Retrieved from https://www.state.nj.us/transportation/refdata/research/reports/FHWA-NJ-2018-001.pdf

Najm, H., Wang, H., Miskewitz, R., Roda, A. M., Ali, A., He, H., Chen, X., Hencken, J. (2017). Technical Brief: The Use of Porous Concrete for Sidewalks. Retrieved from https://www.state.nj.us/transportation/refdata/research/reports/FHWA-NJ-2018-001-TB.pdf

Identifying High Risk Bridges in New Jersey

A team of researchers from New Jersey Institute of Technology have improved upon methods to identify high risk bridges in New Jersey to facilitate prioritization for repair or replacement. They have accomplished this through validating and advancing a new multi-dimensional model to analyze bridge scour and make appropriate recommendations. Bridge scour is the gradual removal of sediment around bridge abutments or piers caused by water movement, which can affect the long-term integrity of a bridge structure. By collaborating with three New Jersey consulting firms, the researchers hope to transfer their findings for statewide application.

Read a short technical brief summarizing the project background and findings (November 2017)

The researchers developed a “Scour Evaluation Model” or SEM that reflects New Jersey’s unique geological and hydrologic/hydraulic conditions while taking a more comprehensive approach than previous practices. NJDOT joins a number of other state DOTs that use a modified method for scour evaluation, as standard methods have often yielded conservative values for scour depth, or yielded disparities between predicted and observed scour.

SEM uses seven parameters to evaluate scour risk. One key parameter is the use of envelope curves, which “correlates the upper range of expected scour depth with a measurable hydraulic variable such as embankment length or pier width.” It was originally developed by USGS and original curves were based on bridge studies in 14 states. Many of the bridges were located in South Carolina’s Coastal Plain, which has a similar geology to New Jersey.

Another key parameter is determining whether a bridge has experienced a 100 year storm, and if so, how it performed. The other five include erosion resistance of streambed, bridge age, field scour observations, channel stability, and HEC-1800 scour calculations.

In their report, the team summarized the impacts of their SEM application. The bridges were rated by priority levels (1-4) based on the analysis. First, 17 bridges were evaluated using an abbreviated SEM procedure to prescreen high risk bridges. These 17 bridges were determined to be Priority 1 (high risk) or Priority 2 (medium-high risk) and in need of repair or replacement.

Secondly, the project evaluated 12 bridges fully using SEM with the participation of three consulting firms. Two of the bridges in the study were found to be Priority 1 (high risk), one bridge was found to be Priority 3 (medium to low risk) and nine bridges were found to be Priority 4 (low risk). The low risk bridges were then recommended for removal from the scour critical list.

Third, the research study was able to validate the use of “envelope curves” to evaluate scour at 15 bridges across 9 New Jersey counties with a range of characteristics and flooding histories.

The team’s goal was to accelerate the transfer of the model into statewide practice, so that it can be fully applied to New Jersey’s inventory of scour critical bridges. This was accomplished through meetings, conference calls and field visits with participating consultants.

The team’s full research and implementation process can be read in the following report:
SCOUR Evaluation Model Implementation Phase

View the team’s presentation slides from the 19th Annual NJDOT Research Showcase