NCHRP 350 (NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM REPORT 350)

WHAT IS NCHRP 350?
The National Cooperative Highway Research Program (NCHRP) Report 350 outlines standardized procedures for vehicle crash testing and in-service evaluation of roadside safety features. These procedures ensure consistent testing and allow engineers to compare the safety performance of different designs tested by various agencies.

SCOPE OF APPLICATION
NCHRP 350 applies to a wide range of roadside and work zone safety devices, including:

• 1. Longitudinal barriers (bridge rails, guardrails, median barriers, transitions, terminals)
• 2. Crash cushions
• 3. Breakaway or yielding supports for signs and luminaires
• 4. Breakaway utility poles
• 5. Truck-mounted attenuators (TMAs)
• 6. Work zone traffic control devices.

PURPOSE AND APPROACH
The purpose NCHRP 350 is to promote uniform testing and inservice evaluation of roadside safety
hardware so that highway engineers may confidently compare the safety performance of designs that
are tested and evaluated by different agencies.

• The procedures are guidelines describing how features should be tested and assessed.
• Policy decisions, such as which features to test, what performance level to achieve, or what criteria are acceptable, are left to individual agencies.
• Factors such as cost, aesthetics, and maintenance are not addressed; the focus is solely on safety performance.

Because it’s impossible to replicate every real-world condition, the report establishes standardized
(normalized) test conditions. For example:

• Straight barriers are tested, even though installations may be curved.
• Tests are conducted on flat grades, even though real sites may be sloped or behind curbs.
• Idealized soils are specified, even though installations may occur in poor or frozen ground.

These normalized conditions simplify comparisons between systems, even though they may affect real-world performance.

CRASH TEST CONDITIONS
Crash tests are designed to subject safety features to severe impact conditions. They specify parameters such as:

• Vehicle mass and type: from small passenger cars to ¾-ton pickups, single-unit trucks, and tractor-trailers.
• Impact speeds: 35 – 100 km/h (≈ 20 – 60 mph).
• Impact angles: 0 – 25 degrees.
• Impact location: defined points on the safety feature.

EVALUATION CRITERIA
Three primary appraisal factors are presented for evaluating the crash test performance:

• Structural Adequacy: the safety feature must contain, redirect, allow controlled penetration, or bring the vehicle to a predictable, controlled stop.
• 2. Occupant Risk: measures the potential hazard to vehicle occupants based on impact velocity against interior surfaces and subsequent deceleration forces.
• 3. After-Collision Vehicle Trajectory: evaluates the vehicle’s post-impact path and its potential to affect other traffic or exhibit undesirable behavior such as pocketing or snagging.

Because crash tests involve complex and sometimes unpredictable conditions, results must be interpreted carefully.

IN-SERVICE EVALUATION
In-service evaluation represents the final stage in the development of new or significantly modified roadside safety features. It assesses how these features perform under real-world roadway conditions, including a range of collision types, environmental factors, and maintenance situations.

This process updates and builds upon the guidelines from NCHRP Report 230, considering the real world complexity of traffic accidents and the limited resources available to monitoring agencies.

APPENDICES
NCHRP Report 350 also includes supporting materials such as:

(a). Commentary on the test procedures’ basis
(b). Soil specifications for the installation of safety features
(c). Specifications for the instrumentation of the tests
(d). A summary on the analytical and experimental tools that can be used in the research and development phase for safety features
(e). A methodology for quantifying the damage to the occupant compartment of a test vehicle
(f). A description of calculation procedures for alternate measures of occupant risk (e.g., THIV, PHD, and ASI) (g). A methodology for conducting and evaluating side impact tests.