Department of Transportation

I-80 Rockfall Mitigation Photo

Rockfall Hazards Overview


The New Jersey Department of Transportation (NJDOT) has jurisdiction of all non-toll interstate and state highways located within New Jersey. As such, the NJDOT has the responsibility to address the rockfall hazards and risks on those highways containing rock cut slopes. In 1994, NJDOT adopted and began using the Rockfall Hazard Rating System (RHRS) for evaluating and ranking highway rock cut slopes. The RHRS is a tool that allows transportation agencies to address their rockfall hazards proactively instead of simply reacting to rockfall accidents. The RHRS provides a standardized way to prioritize the use of the limited construction funds available by numerically differentiating the apparent risks at rockfall sites. This proactive approach has been developed and adopted by the Federal Highway Administration (FHWA) and is the accepted industry standard throughout the U.S.

As part of its rock slope inventory program, the NJDOT has used the RHRS methodology to develop its Rockfall Hazard Management System (RHMS). The RHMS is used to evaluate and rank the stability of all rock cuts within the state highway system. The RHMS evaluates both geologic features and roadway features. It is important to note that the potential for rockfall is the determining factor in the RHMS ratings; motor vehicle crash data is not considered in any of the categories.

There are currently 444 highway cut slopes ranked within the RHMS. Evaluations have resulted in the generation of a rock slope "ranking" matrix.  The Project Area, which is the Interstate 80 (I-80) segment between mileposts 1.04 and 1.45, has been continually characterized as having the highest rockfall hazard rating scores (i.e., highest risk) in the state. The proposed project is a combination of four slopes; although these slopes were scored individually, they need to be looked at collectively as all four slopes are part of one contiguous geologic formation. Due to the geometry and complexity of these slopes and their location in close proximity to the highway, they need to be analyzed as an integrated system in order to address the rockfall hazards at this location.

Rockfall Mitigation Program

Using the data collected from the RHMS, NJDOT has developed a Rockfall Mitigation Program, which is a multi-year program for funding the design and construction of rockfall mitigation projects. The prioritized rankings of highway cut slopes are used to generate mitigation projects that target either a single high-priority cut slope or a bundled group of slopes. Typically, mitigation projects incorporate a main high-priority slope with one or more moderately prioritized slopes for the purposes of cost-efficiency, geographic nearness, similarity of mitigation measures, or minimization of the recurrence of traffic impacts in a local community.

The initial step is a screening of the RHMS priorities identify a single slope or create a bundle group of slopes as a proposed mitigation project. Once a project grouping is screened, it is presented for approval into the Concept Development phase of the NJDOT Capital Project Delivery process.

Mitigation Approaches

The rockfall hazards and risks are evaluated by qualified engineering geologists through geologic mapping and characterization, in general accordance with the recommendations of FHWA's Rock Slopes Reference Manual. The results of the evaluation are presented in the Concept Development Report.

In general, viable alternatives are evaluated following the rockfall hazard mitigation approach hierarchy of:
(1) Removal: Get rid of it.
(2) Stabilization: Don't let it fall.
(3) Protection: Let it fall safely.

Often, a combination of all three mitigation approaches is used to design the most effective and feasible mitigation system.


The removal approach physically eliminates the rockfall source zones, which makes it the most effective method in terms of long-term remediation of the hazards, future maintenance costs, aesthetics, and other impacts. Strategies include mass rock removal through blasting, excavation or reshaping using methods such as trim blasting, hoe-ramming, boulder busting, scaling with prybars, and other mechanical means of removal, as seen below.


Stabilization consists of securing and/or reinforcing the rockfall zone to prevent rocks from moving. Available methods include targeted rock dowels or anchors, cable lashing, anchored mesh, polyurethane resin grouting, shotcrete, and buttressing. The photos below illustrate two types of stabilization techniques: rock dowels and anchored mesh systems. The use of shotcrete and buttressing for the stabilization of shear zones along rock slopes is also a common method. The installation of these designs generally requires specialty contractors with experience executing the methodologies and working on steep slopes where access can be challenging. Permanent mechanical systems require periodic monitoring and maintenance, which should be considered in overall project costs.


Protection involves intercepting and retaining rockfall before it reaches the roadway once the event has occurred. Techniques include the construction of catchment ditches, rockfall barriers and fences, rockfall sheds, earthen or engineered rockfall embankments, and hybrid fence and draped mesh systems that allow controlled rockfall descent. These remedial methods typically involve the most maintenance of the three approaches, as well as more significant visual impacts. Two of the most common protection measures are rockfall barriers and catchment ditches, as shown below.

Last updated date: August 26, 2020 2:35 PM