Tire Tracks & Impressions

Sept 23, 2014

Discovery Science Video

Why study tire tracks & impressions?

Vehicles are used in nearly every crime

Although asphalt roads don’t retain track / impression evidence, many other roads do Off-roads Road shoulders Driveways Run-over objects Snow-covered roads

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

Which measurement do you think is harder for forensic investigators to find?

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

Wheel base is MUCH more challenging to find.

For track width, just need prints of both tires.

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

The front and back track widths are frequently different.

Which is left behind at the scene?

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

The front and back track widths are frequently different.

Which is left behind at the scene?Usually just the back, unless the car is turning

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

Turning diameter – the diameter of the smallest circle a vehicle makes when turning

What information can be learned?

General information about the type / size of vehicle Track width – the distance between the

centers of the two front (or back) wheels.

Wheelbase – the distance between the centers of the front and back wheels.

Turning diameter – the diameter of the smallest circle a vehicle makes when turning

This information may help investigators profile the vehicle used.

What information can be learned?

Individualized evidence that can place a specific car at a scene

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

Noise treatment – variation in size of design across tire, designed to reduce road noise

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

Noise treatment – variation in size of design across tire, designed to reduce road noise

Wear features – as the tires are used, the tread wears down, changing the appearance of tracks and impressions

What information can be learned?

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

Noise treatment – variation in size of design across tire, designed to reduce road noise

Wear features – as the tires are used, the tread wears down, changing the appearance of tracks and impressions

Random individual characteristics – scratches, abrasions, embedded items

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

Noise treatment – variation in size of design across tire, designed to reduce road noise

Wear features – as the tires are used, the tread wears down, changing the appearance of tracks and impressions

Random individual characteristics – scratches, abrasions, embedded items (stones, etc).

All of these can be helpful in linking a car to a scene, but which of these is truly individualized?

What information can be learned?

Individualized evidence that can place a specific car at a scene Tread design – arrangement of grooves and

sipes

Noise treatment – variation in size of design across tire, designed to reduce road noise

Wear features – as the tires are used, the tread wears down, changing the appearance of tracks and impressions

Random individual characteristics – scratches, abrasions, embedded items (stones, etc).

All of these can be helpful in linking a car to a scene, but which of these is truly individualized?

Only random individual characteristics IN CONJUNCTION with the above three features are truly unique.

Wait 30 seconds, then show the answer with your fingers:

Track width is measured from 1. Inside edge to inside edge of two back

wheels2. Center to center of two back wheels3. Inside edge of front wheel to inside edge of

back wheel4. Center of front wheel to center of back

wheel

Quick Review

Wait 30 seconds, then show the answer with your fingers:

Track width is measured from 1. Inside edge to inside edge of two back

wheels2. Center to center of two back wheels3. Inside edge of front wheel to inside edge of

back wheel4. Center of front wheel to center of back

wheel

Quick Review

Wait 30 seconds, then show the answer with your fingers:

A child has been abducted, and police have found tire tracks along the shoulder of the road. What information from the tracks would be most likely to help police profile the suspect’s car?1. Track width2. Tread pattern3. Tire wear4. Wheelbase

Quick Review

Wait 30 seconds, then show the answer with your fingers:

A child has been abducted, and police have found tire tracks along the shoulder of the road. What information from the tracks would be most likely to help police profile the suspect’s car?1. Track width2. Tread pattern3. Tire wear4. Wheelbase

Quick Review

Track width and wheelbase can both help police narrow down possible vehicles, but police are much more likely to find information about track width at a crime scene, as wheelbase measurements require longer, curving tracks.

Wait 30 seconds, then show the answer with your fingers:

Which evidence would be most helpful in convicting a suspect?

1. Track size and wheelbase 2. Track size and turning radius3. Tread design and wear 4. Tread design and noise treatment

Quick Review

Wait 30 seconds, then show the answer with your fingers:

Which evidence would be most helpful in convicting a suspect?

1. Track size and wheelbase 2. Track size and turning radius3. Tread design and wear 4. Tread design and noise treatment

Quick Review

A particular tread design coupled with wear patterns is fairly individualized. Different cars have different tires and will show more/less wear and different wear patterns.

What sort of information can be gained from tire tracks and impressions, and how

can police use this information?

How does this relate to our unit statement?

Closure

Due Thursday: Fingerprint Lab (MAJOR GRADE!) Due Monday: Vocab Miniposters

Homework