Glossary

Countermeasure – an infrastructure improvement, behavioral or enforcement program, or other treatment that is meant to reduce the frequency and or severity of crashes.

Crash-level data – a description of the overall characteristics of a crash event. Datasets may include time, date, location, first harmful event, most harmful event, manner of collision, light conditions, road surface conditions, number of vehicles involved, highest injury severity recorded, and direction of vehicles, among other elements for each crash event. Crash-level data may be further disaggregated into vehicle-level data.

Crash tree – a diagram that shows the breakdown of crashes occurring at an individual location or across a network by selected data elements and attributes. By disaggregating crash datasets in this manner, agencies can identify common characteristics (geometric or otherwise) associated with varying subsets of crashes to narrow the focus of the safety analysis and resulting countermeasure selection.

Evaluation – a post-implementation review of a project, countermeasure, or program to assess its effectiveness. This is the last step of a comprehensive roadway safety management process and can help to inform future policy decisions and target future funding allocations.

Exposure – a measure of the number of potential opportunities for a crash to occur. In the context of BrTS events, exposure generally equates to the traffic volume observed at the bridge or tunnel under consideration.

Focus crash-type – the crash type around which a systemic safety program is built and defined using crash, roadway, person, and other data elements as needed. In the context of this guide, the focus crash-type is a BrTS crash; however, this may be further refined based on elements such as crash severity, structural element struck, or other focus areas defined by the investigating agency.

Focus facility-type – the facility type around which a systemic safety program is built. Typically, this is the facility type on which the largest proportion of focus crashes occurs, on which focus crashes are overrepresented, or on which selection is derived from another program or safety plan. Within the context of this guide, examples of focus facility-types may include bridges, tunnels, over bridges, bridges carrying freeways, bridges with pedestrian facilities, or any other related definition selected for safety analysis.

On-bridge (or in tunnel) collision with superstructure – a crash that occurs while a vehicle is traveling over a bridge or within a tunnel and involves a component of the bridge superstructure (e.g., railing or truss) or tunnel walls.

Overheight vehicle – vehicles and loads beyond legal size limitations or standard-size vehicles beyond a local height limitation of a specific bridge or tunnel.

Overrepresentation – the comparison of the proportional distribution of a set of subject data to a set of comparison data with the goal of identifying attributes for which the subject data accounts for a notably larger proportion than the comparison group. For example, if one out of 30 bridges in a jurisdiction accounts for 20% of all reported over-bridge crashes, that bridge and crash type combination is overrepresented within the network.

Performance measure – a quantitative, qualitative, or hybrid indicator used to prioritize locations for further investigation or to assess the effectiveness or efficiency of projects, countermeasures, or programs. Crash-based performance measures may include the number of crashes by type and/or severity. Risk-based performance measures may include the risk score for a given location or the percentage of the system with a risk score exceeding a specified threshold. Operational performance measures may include operating speeds, driver compliance, and driver response.

Risk – made up of two elements: a qualitative or quantitative measure of the likelihood of a BrTS event and a quantitative or qualitative measure of the impacts (road closures, infrastructure repairs, crash consequences, crash costs, etc.) of such an event given that one occurs.

Risk score – a quantitative measure based on the presence and weight of risk factors for each element being considered in a safety analysis. Ranking potential project locations by their total risk score can help agencies identify and prioritize locations with the greatest opportunity for safety improvements.

Severe crash – the subjective definition in the context of this guide depending on the performance measure of interest. May be defined by a jurisdiction using an injury category (such as fatal and suspected serious injury), a threshold of resulting structural damage, or some combination of related elements.

Site-level data – summary of data for an individual location, such as a bridge or tunnel structure. This may include crash, roadway, traffic, and structure datasets among others.

Systemic safety – a proactive form of safety management in which agencies install proven safety countermeasures at locations that are prioritized based on their relative level of risk.

Target crashes – the subset of crashes for which analysis and countermeasure applications are focused. For example, an agency may select BrTS crashes as their target crash dataset for safety analysis, or they may choose to refine their definition further to target over-bridge crashes involving heavy vehicles striking outside barriers. Some countermeasures specifically target certain crash types, such as lighting improvements to reduce nighttime crashes.

Under-bridge (or entering tunnel) collision with substructure – a crash that occurs while a vehicle is traveling under a bridge or entering a tunnel and involves a component of the bridge substructure (e.g., supports) or tunnel entrance.

Under-bridge (or entering tunnel) collision with superstructure – a crash that occurs while a vehicle is traveling under a bridge or entering a tunnel and involves a component of the bridge superstructure (e.g., girder, truss) or tunnel entrance.

Vehicle-level data – the characteristics of each vehicle involved in a crash event. Datasets may include a description of damage, insurance company information, make and model of vehicles, registration, number of occupants, travel direction, and sequence of events before the crash, among other elements.