ClosingSpeed app for iPhone and iPad

The closing speed application is designed to work the change in velocity data obtained from an ACM download (CDR data) or other source, such as a crush analysis, along with a single post impact speed to determine impact speeds of the involved vehicles in in-line collisions.

By working with a change in velocity the collision investigator can avoid the need of having to know 3 of the 4 involved speeds in in-line or collinear collisions, which generally requires the investigator to assume an impact velocity of one of the involved vehicles. Since this approach only requires the use of a single post impact speed, it further reduces the errors that are associated with determining the post impact braking percentage of vehicles involved in a collision.

When using this application, the user enters a single change in velocity and then identifies the vehicle it came from. Since many ACM downloads only report the change in velocity in Imperial units (mph) it may be entered in mph even when working with Metric units, the application will convert the value to km/h.

The post impact velocity of one of the involved vehicles is entered. If the collision is a head-on collision, the user will have to identify if the vehicle was driven backwards or changed direction as a result of the impact.

The weights (masses) of both vehicles are entered along with the collision configuration; head-on, rear-end or a collision involving a stopped vehicle.

After the data has been entered the “Results” screen will display the impact velocities, post impact velocities, and change in velocities of both vehicles. In addition, it will display the closing and separation velocity of the collision. All of the velocities will be displayed in units of both mph and fps when working in the Imperial system or km/h and m/s when working in the Metric system.

On the result screen the collision restitution is control by a slider and may be changed by simply moving the slider from side to side. This will simultaneously update all of the related calculations, permitting the user to determine how sensitive the restitution value is to the overall velocity calculations.

The calculation screen will display all of the calculations in a line-by-line or step-by-step fashion. The calculations displayed include:
Impact Velocities
Post Impact Velocities
Closing Velocity
Separation Velocity
Change in Velocity