Overview

AASHTOWare Safety Alternative Design enables designers, planners, and safety engineers, to run Part C calculations found in the Highway Safety Manual.

Alternative Design calculates the safety improvements made by designers, planners, and safety engineers, through changes made to roadway characteristics including lighting, shoulder size, lane width, etc. The AASHTOWare Safety Alternative Design application produces reports that demonstrate comparisons between multiple proposals for metrics such as crash reductions and benefit-cost ratios.

The Alternative Design application includes four modules, and includes Empirical Bayes calculations for each of the modules:

Alternative Design will receive ongoing updates for newly developed calculations, including the forthcoming Highway Safety Manual Version 2 Part C, which includes bike and pedestrian modules.

For more information regarding Alternative Design, including key terms used in this article, see the Alternative Design - Key Terms article.

Alternative Design is broken into five sections, each of which is discussed in more detail below:

The Project Selection section is where you select the segment, or intersection that will be the focus of your project.

(The Project Selection screen for a new Alternative Design project, with no segments or intersections selected.)

By clicking the +Add Segment button you can add a segment to the project. After clicking the button, you will be prompted to select the endpoints on the desired segment from the map.

(Selecting a Segment to include in the project)

After selecting the segment, it will be added to the current project, and displayed in the segment summary on the right side of the screen.

Intersections are defined by the user for each project, and can be added by clicking the +Add Intersection button. Begin selecting one of the legs of the intersection by clicking on the two endpoints for the first leg of the intersection. After selecting the first leg, you can add each additional leg of the intersection by clicking the +Add Intersection Leg button under the indicated intersection.

(Adding the second leg to the intersection)

After all Segments and Intersections have been added to the project, click the blue Continue button to proceed to the Current Condition tab of the design project.

Users can create a road segment within an Alternative Design project. Select “New Proposed Segment” and draw at least two points on the map to generate the new road.

(Select “New Proposed Segment” to create the new road within the Alternative Design project.)

(Users can select at least two points on the map to represent a new segment of road.)

Once the points are selected, click “Done,” and the new segment will appear as a dashed line on the map.

(The newly created segment is displayed as a dashed line on the map.)

Click continue or select “Current Condition” from the top menu bar to input additional information about the segment.

The current condition tab is where you define the current state of the roadways involved in your project. You will need to populate the roadway information, and details for each Segment and Intersection included in your project. This is done by filling out each field listed under each Segment or Intersection listed in the left sidebar of the screen.

Under the information section, you can name each Segment or Intersection, and define the Roadway Type, and volume information for the selected roadway. Note that the AADT information will be populated automatically for the selected Segment/Intersection.

(The Information Tab for the selected segment, with the Roadway Type, and AADT fields populated)

(The Information Tab for the selected Intersection with the roadway type, intersection type, and AADT fields populated)

The Roadway Details section will require you to populate roadway characteristics for each of the Segments and Intersections selected. The fields will change depending on the roadway or intersection type selected.

(The Roadway Details section of a given Segment)

The Bike and Pedestrian Details sections will require you to select any relevant roadway characteristics for each of the Segments and Intersections selected. The fields will change depending on the roadway or intersection type selected.

(The Bike details section of a given Segment)

The Crashes section summarizes the historical crash data that has been populated from the selected Segments and Intersections. To explore the crashes included in a location, click the Open in Crash Query button, and a new tab will open to display the selected location, and all associated crashes.

(The Crashes section of a given Segment)

The No-Build section contains several variables that must be defined in order to complete your project. This includes AADT growth, cost of the no-build project, and any notes associated with the no-build scenario.

(The No-Build section of a given project)

The Summary section summarizes the Expected Crashes over a 10 year total, based on the No-Build scenario. These results are based on the Segment and Intersection details defined in the previous sections of the Current Condition tab.

(The Summary section for a project)

The Proposals section allows you to add multiple proposed changes to each of the locations in your project. These projects will be compared to the current condition, and are required in order to complete a comparison summary. While at least one proposal should be included for each project, multiple proposals can be added. Each additional proposal will be included in the Comparison Summary section of the project.

To add a new proposal to a project, click the +Add Proposal button, in the top right corner of the project screen. This will add a new tab to the project navigation bar, titled Proposal 1.

Click the Proposal in the project navigation bar, and begin to enter the new proposed state for the project.

Each Proposal will display the Segment and Intersection characteristics for the project. Here you can enter proposed changes to any of the existing roadway characteristics, and determine the safety impact of those changes. As a change is made to the current conditions, the Adjustment Factor, and any changes to the Adjustment Factor are highlighted to the right of the proposed change.

In the example below, Segment Lighting has been added to the selected Segment, where it was previously not present. Note the change to the Adjustment Factor (AF).

(The Roadway Details tab of a proposal, indicating a reduction in crashes associated with adding Segment Lighting to the roadway).

Changes can be made to the Roadway Details, Bike Details, and Pedestrian Details sections for each roadway in your project. By default, the current condition will be populated in each field, so only the changed conditions need to be indicated in a proposal.

Before completing a proposal, ensure that the Cost section has been completed. This indicates the cost associated with any proposed changes. You will need to enter the Construction Cost, Maintenance Cost, and Service Life of the proposed improvements. These values can be entered for each individual treatment for each Segment or Intersection, or as a single Total value.

(The Cost section for the Segment Lighting proposal)

The Summary section will illustrate any changes associated with the selected improvements.

(The summary page for the selected proposal)

The Comparison Summary tab summarizes the metrics and calculations associated with each of the proposed projects, as well as the no-build scenario.

From this screen, the various projects can be compared to each other, and the design with the greatest impact, and benefit cost ratio can be easily identified.

(The Comparison Summary screen, comparing the two proposed projects, with the no-build scenario)

(The Comparison Summary screen, comparing the two proposed projects, with the no-build scenario, including the Benefit Cost comparisons for each project)

Reference Table

The Reference Table section displays the tables from the Highway Safety Manual that are used in the project. These tables are based on roadway type.

(The Reference Table for the selected project)

An Alternative Design report can be downloaded for any saved Alternative Design. To download the report, click the Download icon located in the menu bar at the top of the screen (Note: if the Download icon is not displayed, it is likely because the project has not yet been saved).

A report preview will open displaying the formatted report. To download the PDF of the report, click the Save & Download button located in the top right corner of the screen.

(The report preview screen of the selected project)