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Highway / Roadside / Traffic Safety
Expert Consulting & Expert Witness

RoadSafe LLC provides highway, roadside, and traffic safety expert consulting services in the specific areas listed below. Expand any section to learn more about the service. Please inquire to Christine E. Carrigan, P.E., PhD about these services.


The frequency of fatal and serious injury crashes is a product of the probability of a vehicle leaving the travel lanes and encroaching onto the roadside or median, the probability of crashing with a roadside object given that a vehicle has encroached, and the probability of a fatal or serious injury crash outcome given that a crash has occurred. Risk analysis determines if roadside hardware increases or decreases the risk of a fatal or serious injury for the range of roadside design alternatives considered. Our traffic safety experts have unparalleled experience in the risk analysis of roadside design alternatives and have developed guidance for use by the American Association of State Highway and Transportation Officials (AASHTO) and State Departments of Transportation (DOTs) for conducting risk analysis of roadside designs.

Benefit-cost methods have been used in roadside design for over 40 years to balance improvements to safety with implementation costs. Benefit-cost methods compare the risk reduction to the capital cost increase for each roadside design alternative. Our cost-benefit experts developed the Roadside Safety Analysis Program version 3 (RSAPv3), the computer program currently cited by the AASHTO Roadside Design Guide and by numerous states for conducting benefit-cost analyses.

The AASHTO Roadside Design Guide defines the clear zone as “the total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles. This area may consist of a shoulder, a recoverable slope, a non-recoverable slope, and/or a clear run-out area. The desired width is dependent upon the traffic volumes and speeds and on the roadside geometry.” Our clear zone experts have led research on the probability of rolling over on roadside slopes and research on the frequency and severity of crashes with fixed objects such as trees, poles, and signs on the roadside.


Numerous bridge railings have been designed in the past several decades to contain and redirect passenger sedans and pickup trucks. A smaller number of bridge railings have been designed to capture and redirect heavy vehicles such as single-unit trucks and tractor trailers. The designs for the various vehicle types are categorized by test levels. Our bridge railing experts have conducted research, designed, and analyzed bridge railings for both passenger vehicles and heavy vehicles and developed criteria for the selection of the appropriate test level bridge railing based on specific vehicle and site characteristics.

The shielding of bridge piers or columns involves the consideration of the potential for catastrophic impacts from heavy vehicles and the occupant risk of impacts from passenger vehicles. Site conditions, traffic conditions, bridge layout, and the geometry of the roadway section passing beneath a bridge are all important characteristics for choosing the most effective barrier. Minimizing the chance of catastrophic bridge collapse in a heavy truck impact is another vital consideration when assessing the roadside design around bridge piers. Our bridge pier/column experts developed the guidance for shielding bridge piers/columns that has been implemented by AASHTO.

Median barriers are intended to reduce the risk of an errant vehicle crossing the highway median and striking or being struck by another vehicle in the opposing lanes. The decision to use a median barrier, the selection of the appropriate median barrier, and the placement of the median barrier is based on traffic volume, the proportion of heavy vehicles in the traffic mix, the median geometry, in-service performance, and barrier type (e.g., cable barrier, metal beam barrier, concrete barrier). Our median design and barrier experts have developed guidelines for the selection and placement of median barriers for incorporation into the AASHTO Roadside Design Guide and state guidance.

The AASHTO Roadside Design Guide (RDG) and the appropriate state design practices outline the engineering guidance supporting the decision to use or not use roadside barriers. The RDG provides guidance on how to select, locate and place roadside hardware. Our roadside design experts have conducted numerous research projects to develop new guidelines for the use of roadside hardware and have developed barrier selection, use, and placement guidelines for incorporation into the AASHTO Roadside Design Guide and state guidance.

An end treatment is the designed modification of the end of roadside barrier or median barriers including anchorages, terminals, and crash cushions. Our experts have designed, crash tested, and evaluated the field performance of a variety of end treatments.


The objective of an ISPE is to assess the crashworthiness of safety features under field conditions. A secondary objective is to determine which factors influence performance (e.g., maintenance, installation, hardware design, etc.). Consistent with the crash test evaluation criteria in MASH, safety feature performance is assessed through consideration of (1) structural adequacy, (2) occupant risk, and (3) vehicle trajectory with the greatest consideration being given to occupant risk. Our team is composed of some of the most accomplished roadside safety researchers currently active in the collection and evaluation of in-service hardware performance data.

Roadside safety features such as longitudinal barriers, sign supports, guardrail terminals, and work zone devices generally demonstrate successful performance according to the currently adopted crash test and evaluation criteria in order to be eligible for Federal-aid funding on the National Highway System and/or to be put on a State’s qualified products list. Crash testing is a direct means of assessing roadside hardware for occupant risk, structural adequacy, and post impact vehicle trajectories under specified impact conditions. NCHRP Report 230 was published in 1981 to provide guidelines for performing and evaluating full-scale vehicle crash tests. In 1993, NCHRP Report 350 was published. AASHTO published the Manual for Assessing Safety Hardware (MASH) in 2009 and updated it in 2016. Our roadside hardware experts have extensive experience in assessing the performance of roadside hardware using crash tests.


Highway engineers use established design guidelines as a means for producing a “safe” design. These established design guidelines include: A Policy on Geometric Design of Highways and Streets (i.e., the “AASHTO Green Book”) and the AASHTO Roadside Design Guide (RDG). Each of these design manuals provide the designer with a set of guidelines for designing a roadway. The current design guidance allows for flexibility in application of design principals, is long-established, and rooted in the design community. The practice itself, however, has evolved in recent years to incorporate an improved understanding of the consequences (e.g., construction cost, capacity, highway safety, etc.) of design decisions.

Title 23 USC 109 provides that projects not on the national highway system (NHS) are designed, constructed, operated, and maintained in accordance with State standards. Standards for projects on the NHS are approved by the Federal Highway Administration (FHWA) after development by the States. Our highway safety experts have unequalled experience in the development, application, and assessment of national and state design guidance.

The Manual on Uniform Traffic Control Devices (MUTCD), published by FHWA, is the national standard for designing, applying, and planning traffic control devices. States have two years to adopt each new edition of the MUTCD. The MUTCD says “… State transportation agencies differ in how they comply with MUTCD standards. For example, some States adopt the national MUTCD as their standard. Other States adopt the national MUTCD along with a State supplement … other States use the national MUTCD as the basis for developing their own State Traffic Control Device manuals….” Our highway safety experts have significant experience in the application of the MUTCD and assessment of projects according to the MUTCD.

Highway construction is generally conducted in conformance with the design documents through incorporation into the construction contract (e.g., plans specifications, and estimates). Explicit consideration of maintenance of traffic (MOT) through construction activities provides for both safe and efficient travel for the public and minimizes the risk to workers within the construction zone. Both the AASHTO Roadside Design Guide (RDG) and the FHWA’s Manual on Uniform Traffic Control Devices (MUTCD) provide guidance for the maintenance of traffic during construction. Our highway safety experts have extensive experience in development, review, and assessment of construction plans and specifications.

Our Service Area

Roadsafe LLC has professional engineers registered in the States of Arizona, Connecticut, Florida, Hawaii, Illinois, Indiana, Maine, Massachusetts, Mississippi, New Mexico, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Texas, Virginia, Washington state, and West Virginia. Our professional engineers maintain a NCEES model law record to allow for efficient registration in additional states.


Christine Carrigan

Christine Carrigan

For Highway / Roadside / Traffic Safety Expert Consulting Services, contact Christine Carrigan.



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