| Roadway geometrics
Geometrics define the normal roadway operating environment. Frictional properties, construction materials, wear, width, cross-slope, super-elevation, horizontal and vertical curvature, roadside design, traffic signs, maintenance, ride quality, average daily traffic, traffic mix, designed use, and structural integrity are all of interest and concern in the reconstruction of an accident. Click images for enlargement.
Documentation of the roadway environment and collision related physical evidence is critically important in most collision reconstruction cases. Often the roadway itself is named as a causal link or contributor to the collision. CRA documents the roadway environment to determine what, if any, role it played in the collision sequence. Surveying CRA surveys the collision environment using the Nikon NPL-350 Total Station survey instrument. This Nikon surveying system allows all roadway geometric data and physical evidence to be collected at the scene and subsequently downloaded into a computer drafting program at a different location. This state-of-the-art technique assures the data will be more accurate, precise, and reliable. The Nikon surveying system is extremely accurate in all types of terrain and traffic conditions. Scene surveys and physical evidence documentation are quickly and reliably captured. Degraded collision physical evidence can be recreated using photogrammetry and/or matching roadway characteristics and photographs. A full size color plotter is used to print survey information and computer generated graphics for presentation.
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Physical Evidence Collection CRA can secure and store physical evidence retrieved from the scene or any of the vehicles involved in a case. An example would be to secure a taillight from a vehicle involved in an accident. Studying the taillight filament could provide a determination as to whether or not the bulb's filament was illuminated at the time of impact. Microscopic evaluations and photographs using standard microscopes and Scanning Electron Micrographs can also be made of the failed tungsten filament to conduct a scientific analysis on filament deformation, breakage, crack propagation, or fatigue. Lighting Roadway lighting is sometimes a factor in the occurrence of a collision. Ambient lighting, headlights, moisture conditions, and various vehicle factors make up a complex set of conditions that dictates the probability of an object or roadway geometry being conspicuous. For example, the various materials used in the construction of roadway surfaces tend to reflect light in different ways. This has a significant effect on the contrast recognition of objects and vehicles on the road.
The investigation into the conditions under which a collision occurred should include a roadway lighting analysis. Friction Evaluation Friction can be thought of as the resistance between two surfaces when they are in contact. The friction generated between any two surfaces is important in reconstruction since friction dictates motion and can convert kinetic energy to heat, noise, and deformation of materials. Work/Energy relationships are significant when the calculation of acceleration, speed, time and distance of a vehicle is desired. In most collision cases, friction between the roadway and tire is analyzed, however metal-to-pavement and metal-to-soil contact can occur in rollover collisions and in motorcycle pre- and post- impact trajectories. CRA reconstructionists have extensive experience and expertise in conducting pavement friction research studies for various State Highway and Transportation Departments, as well as for the U.S. Department of Transportation's Federal Highway Administration. Friction testing and analysis is commonly performed on collision cases analyzed by CRA. |
Pavement and Shoulder Conditions
Pavement and shoulder conditions can play a role in the occurrence or avoidance of an accident. Bumps, potholes, pavement roughness, and pavement edge drop-off are just a few of the pavement conditions that may cause difficulty for some drivers.
Roadway departments must follow standards, regulations, and guidelines to maintain safe driving environments. CRA has extensive experience and familiarity with these roadway construction and maintenance practices. Signing and Traffic Control Signing, traffic control, highway layout, and design, the Manual on Uniform Traffic Control Devices (MUTCD), the American Association of State Highway Transportation Officials (AASHTO), and the Roadside Design Guide recommendations and guidelines all fall into the area of transportation engineering and highway safety.
Areas outside of the U.S. have similar guidelines that must be followed to provide a homogeneous driving environment for the traveling public. CRA associates have extensive experience in the teaching, practice and implementation of this field. Traffic routing, guidance, compliance with state and federal regulations and guidelines and conformance with prudent safety practices can be determined for each collision case. Crash Cushions and Utility Poles CRA associates have extensive experience in the design and testing of various crash cushion, guard rail systems, median barrier systems and break-away roadside objects. CRA has many references and studies, written by CRA associates and others, at its disposal to assist in the reconstruction of collisions involving roadside objects. CRA has the capability to conduct full-scale crash testing of existing or new rail designs.
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