How to Read the Tool Descriptions

Each transportation engineering tool within this Toolbox includes a description of each of the following aspects of the tool:

• Safety Benefits
• Street Types
• Land Use Context
• Primary User Groups
• Key Implementation Considerations
• Expected Crash Reduction
• Cost
• Timeline
• References

Safety Benefits 

Broad categories of safety benefits for each tool include:

• Speed reduction,
• Crossing improvements,
• Visibility improvements,
• Conflict reduction, and
• Transit access improvements.

Street Types

Each road or trail in Arlington County may not have the same characteristics, so the same tool may deliver different results from one location to another. Choosing the best tool for a specific location depends on factors like street characteristics, number of travel lanes, geometry, vehicle speeds, and volumes. For example, some treatments are more appropriate for use on neighborhood roads while others are better used on arterial streets with higher traffic volumes.

Arlington’s streets are categorized using “functional classifications,” which provide a basic idea of how people use the road. Below is a summary of the Arlington County street network functional classification as defined in the County’s most recent Master Transportation Plan Streets Element. See the Appendix for a map of the County’s Street Network Functional Classification. The Toolbox identifies for which street type each tool is applicable.

Controlled-Access Highways

Primary User Groups

Most tools provide safety benefits for all roadway users but may provide different benefits across different transportation modes. The main types of roadway users expected to benefit from or use each tool are indicated with the following icons:

Key Implementation Considerations

Each tool description lists factors that may impact its implementation. These often include aspects specific to the engineering of a particular tool and the roadway and environment in a location considered for implementation. Nearby bus routes and Metro/bus stops, as well as other connecting transportation facilities (nearby streets, trails, bridges, bikeshare stations, or pick up-drop off areas), are other required considerations. Other key factors that could impact the ease, cost, or timeline of implementation are also noted.

Expected Crash Reduction

Transportation researchers have estimated the probability of a tool to reduce crashes (measured as a percentage). This Toolbox highlights research-based crash reduction estimates for each tool when available. When research-based crash reduction estimates are not available, the Toolbox provides other research to indicate potential safety outcomes.

Note: According to the Federal Highway Administration (FHWA), crash reduction estimates should be regarded as a generic guide for understanding the impacts of a safety tool. Environmental, traffic volume, multimodal, geometric, and operational conditions may impact a tool’s effectiveness. Engineers must use professional judgement and consider local factors when considering the best tool for a location.^[1] Deploying multiple tools at the same location may have complementary safety benefits.

Cost

The cost ranges listed for each tool include estimates for planning, engineering, installation, and maintenance. Some tools require monitoring and maintenance to ensure they remain effective throughout their lifecycle. Tools that require significant ongoing maintenance are less desirable for application than those that require minimal maintenance and are indicated with a tool icon.

Cost categories for each tool in this Toolbox are as follows:

Timeline

The timeline ranges listed for each tool include estimates for planning, engineering, and implementation. Timeline categories listed for each tool are as follows:

Definitions & References

[1] Federal Highway Administration, Crash Reduction Factors (2014), https://safety.fhwa.dot.gov/tools/crf/