- Email: [email protected]
Vehicle Tire Marks and Tire Track Measurement
P PATTERN EVIDENCE
Contents Vehicle Tire Marks and Tire Track Measurement Plastic Bag Striations Bare Footprint Marks The Friction Ridge Skin of the Feet Palm Prints Footwear Marks Serial Number Shotgun Ammunition on a Target Physical Match Tools Analysis, Comparison, Evaluation, and Verification (ACE-V)
Vehicle Tire Marks and Tire Track Measurement WJ Bodziak, Bodziak Forensics, Palm Coast, FL, USA ã 2013 Elsevier Ltd. All rights reserved.
Introduction
Sidewall Information
In today’s highly mobile society, criminals often use vehicles to travel to and from the scenes of the crimes they commit. Their vehicles track over surfaces such as sand, soil, and snow, which will often retain the impressions of one or more tires. There are two forms of tire evidence potentially left at the scenes of crime. Tire marks or tire impressions are those left by the tread design. Tire tracks leave dimensional information exclusive of the tread design, and include track width, wheelbase, turning radius, as well as the relative positions of the tracks of all four tires. Tire evidence ranges from a partial impression of one tire to a full set of tracks representing all four tires. Often details produced are sufficient to provide evidence of a vehicle’s presence. Proper recovery of this evidence, through good notes and crime scene drawing measurements, photography, and casting, serves as a way of preserving the evidence for subsequent comparison with the tires and track dimensions of a vehicle. Figure 1 gives some basic nomenclature.
Much information is molded into the sidewall. Portions of that information are of importance to the investigator and examiner, and should be noted when investigating or examining any tire. First noted should be the brand name and style name, such as Michelin XMþS 244 and the size of the tire, such as P 195 75/R 14. Also of importance is the United States Department of Transportation (DOT) number, which will usually begin with the letters DOT. Because of the worldwide tire market, this information will be found on tires made in any country. The DOT information is now required to be on both sidewalls. The DOT number will be similar to the following example:
Encyclopedia of Forensic Sciences, Second Edition
DOT Department of transportation
HM
L9
Manufacturer Size code and plant code Michelin Tire Stoke-on-Trent, England
ABCD
4911
Optional symbols for manufacturer
Date of manufacturer 49th week of 2011
In this example, the two letters following the DOT number, such as HM, are symbols for the manufacturer and plant code. By
http://dx.doi.org/10.1016/B978-0-12-382165-2.00273-7
1
2
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
Groove Rib
Center line Sipe
Design element Slot or lateral groove Lug
Tread surface
Tread wear indicator (wear bar)
Belts Radial plies Inner liner White sidewall (a)
Bead wire
(b)
Bead wrap
Figure 1 (a) and (b) Radial tire: basic terminology.
looking this code up in a reference source, such as who makes it and where, or searching the Internet for ‘tire plant code HM,’ the specific plant in this example can be identified as the Michelin Tire Company, located in Stoke-on-Trent, England. The next letter and number are the tire size code. The following four letters, for example, ABCD, are optional and are the manufacturer’s symbols. The last four numerical digits are important, as they indicate the week and year in which the tire was manufactured. For example, the numbers 4911 in this example would indicate the tire was made in the 49th week (49) of 2011 (11). Tires made prior to the year 2000 only had three numbers, thus a number here of ‘491’ would indicate the 49th week of 1991. Retreaded tires have a slightly different DOT number on them. The retread DOT number will begin with the letters DOTR or perhaps just R. The original DOT number that was on the new tire should still be present, so it is likely that a retreaded tire will have both a DOT and a DOTR number on it. The DOTR number consists of three letters and three numbers and would be similar to the following example:
In this example, the three letters are a code to identify the retreading facility. A publication, Who Retreads Tires, lists approximately 5000 retreading facilities by their three-letter code. The four numbers identify the week and year of retreading.
will have its plies running at a bias angle across the tire. A biasbelted tire will have the same plies, but will have the addition of a belt beneath the tread area. While bias and bias-belted tires were predominant many years ago, only some large truck tires and tires for large construction equipment will likely be found to still have bias construction. Bias and bias-belted tires are less effective at reducing tire squirm, that is, the degree of contraction of the tire tread while under load. Thus, the impression left by a bias or bias-belted tire may appear to have a narrower appearance than what appears on the tire itself. A radial tire will have the plies running in a radial direction, from bead to bead. Radial tires, because of the radial direction of their plies, reduce the amount of squirm, and result in almost no difference in dimension. In an examination, test impressions of the tire made while under load on a vehicle are necessary to provide a comparable dimensional standard for comparison with a crime scene impression. Tires are built of many components, including a liner, sidewall components, the bead, plies, belts, and tread rubber. These are assembled on a rotating and collapsible drum. After assembly of the components, the ‘green tire,’ whose tread rubber contains no tread or sidewall design at this point, is transferred to a mold. In the mold, under extreme heat and pressure, the various tire components will be vulcanized and bonded together. A steampressured bladder will inflate inside the tire and press the green tire against the surfaces of the mold. It is here that the tread and sidewall designs will be molded into the rubber.
Tire Construction
Tire Designs and Databases
There are three basic types of tire construction that have been used in tire building: bias, bias-belted, and radial. A bias tire
There are thousands of designs of tires, including those made for passenger vehicles; light, medium, and heavy trucks;
DOTR
YPY
1211
Retreated tire
Goodyear Retread Frederickton, NB Canada
12th week of 2011
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
agricultural vehicles; off-the-road vehicles; and motorcycles. Since the 1960s, the Tread Design Guide® (Tire Guides Inc., Boca Raton, FL, USA) has offered a listing and photographs of most tire designs. This guide is published annually in hard copy form and up through 2010, a more comprehensive version on a CD-ROM known as Tread Assistant, which included over 18 000 tire designs, was produced. The CD version was discontinued with the year 2011. The CD version was subdivided by the type of tire category, that is, ribbed tire, metric, lugged tire, and so on, allowing for easier search on a PC computer format. In recent years, a new database known as TreadMate® (Foster & Freeman Ltd, Vale Park, Evesham, Worcestershire, WR11 1TD, UK) has been launched. These sources provide the investigator a method of linking a crime scene impression to a specific tire design and manufacturer. Once done, additional information of relevance can be sought from the respective manufacturer if needed.
Original Equipment Tires Versus Replacement Tires Original equipment manufacturer (OEM) tires, usually referred to as just ‘OE’ tires, are those which are put on a vehicle when it is manufactured. Replacement tires are those which are purchased to replace the OE tires, or other replacement tires, when they wear out. A particular vehicle with its four OE tires will not be a rare occurrence, as many thousands of those vehicles would have been sold with the same design and size of OE equipment. On the other hand, a vehicle with one or more replacement tires on it constitutes a much less frequent occurrence, as other vehicles of that type and brand are less likely to have the same combination of brand and style replacement tires. A vehicle with three or four different designs of replacement tires in a particular size constitutes a rare occurrence that would probably not be repeated, owing to the large number of available designs and sizes.
flatter and proportionally wider, whereas a tire with a higher profile, such as 70, appears more conventional. Today, an increasing number of passenger cars are equipped with lowprofile tires to increase traction and performance.
Noise Treatment Tires produce noise for many reasons. Noise is generated differently as a tire crosses different surfaces, such as from asphalt to concrete. Noise is also generated as air is trapped in the void areas of the tread design upon impact with the substrate, creating a noise when it escapes. In addition, the individual tread blocks will vibrate, creating noise notable at higher speeds. Manufacturers attempt to treat and reduce this category of ‘noise’ by varying the pitch, or size, of the tread blocks as they are positioned around the tire. The sounds emitted by varied pitches create better harmonics than the sounds emitted by the same pitch repetitively. The industry refers to this as ‘noise treatment.’ Noise treatment originally involved creating three sizes of tread blocks (design elements), that is, s, m, and l (or 1, 2, and 3). In some cases, the tread blocks may follow a 1,2,3,1,2,3,1,2,3,. . . arrangement around the tire. Or, they may have an arrangement of those same three sizes, but in a more random order, such as 1,3,2,2,3,1,2,3,1,1,2,3,3,2,2,1 and so forth. In other cases, more complex and varied arrangements, including more than just three different sizes, may involve a pattern such as 1,2,3,4,4,3,2,1, 3,3,2,2,2,2,3,3,4,3,2,1,1,2,3,4, and so forth. An example of such an arrangement is illustrated in Figure 2. In this example, the noise treatment consists of 64 design elements of four different sizes. They are arranged in four
A B C D
12344321 4321 1234 22 33 33 22 33 2222 33
D A
4
3
3 3 2 2 2 2 3 21 3
4
4
Tire Size Designations
3 2
1
32112 3 4 2 4 32
1
2 3 4 4 3 2 4 1 1 23 2
1/
th
3
3
6
3
3
2 32
2
2
1 2 3 4 43 2 1
The aspect ratio, otherwise known as the tire profile, is the relation of the height of a tire to its width. The appearance of a tire with a low profile or aspect ratio, such as 45, will look
3
Aspect Ratio
3
Metric: 195R14; 195, approximate section width in millimeters; R, radial tire; 14, rim diameter; P-Metric, P 195/75 R 14; P, passenger tire; 195, approximate section width in millimeters; 75, aspect ratio; R, radial tire; 14, rim diameter.
2
C
Newer Designations
B
1
B
Numeric: 6.45–14; 6.45, approximate section width in inches; 14, rim diameter; Alphanumeric: E R 78–14; E, load/size relationship; R, radial tire; 78, aspect ratio; 14, rim diameter.
3
2
Tire sizes have been designated in a number of ways throughout the years. The tire size designations that have been used are shown below.
Older Designations
3
C
A
4 3
3 2 1 1 4
4
2 3
3
2 2 3 3
2 1 3 3 2 2
Tire impressions
Figure 2 Noise treatment example.
A
4
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
sequences, represented by models A, B, C, and D. The six treadwear indicators are also included in Figure 2. The lower part of the figure represents a crime scene impression. Note that only one possible area of the tire could have produced the noise treatment in that impression. This is because the portion of noise treatment for model A plus the portion of model D, as shown in Figure 2, does not repeat elsewhere in the tire. Tires were originally produced with a nondirectional noise treatment, that is, the pitch sequence was identical on both sides of the tire as shown below. With this form of noise treatment, the tire will leave an identical repeating sequence in either direction. Examination of a crime scene impression made by a tire with nondirectional noise treatment would not enable determination of the direction of the vehicle based on this alone.
(0.16 cm) above the base of the grooves. In this way, as the tire wears down, the wear indicators will appear as bald strips across the remaining tread design. Tread-wear indicators are visible in a two-dimensional impression only if the tire is worn down to that level. They may be visible in three-dimensional impressions if the tire had produced a deep enough impression in the substrate. Tread-wear indicators will occur in different portions relative to the noise treatment of that tire. Each tread-wear indicator will therefore be in a different portion of the noise treatment arrangement (Figure 2). This can be of further assistance in locating the precise portion of the tire that made the impression.
1 2 31 2 3 1 2 31 2 31 2 3
The noise treatment of tires is used whenever possible during the examination of tire impressions, as it assists in locating the possible position on the tire that could have made a particular impression. An average passenger or light truck tire may have 2 m or more of tread in a full circumference impression. A crime scene photograph or a cast of a tire impression may only be 0.25–0.5 m in length. If it is of sufficient length, the crime scene impression will only match one location around the circumference of the tire that made it. Once that position is located, it will then be additionally examined for evidence of wear and acquired individual characteristics. Recovering longer segments of impressions at crime scenes allows for a more specific determination of the portion(s) of the tire that made the impression. Every examiner who conducts forensic tire impression examinations should be knowledgeable about tread design noise treatment and how it is significant in the comparison process.
Known standards of tires fall into two different categories. They include those obtained for tires that differ in design from the questioned impression such as police and emergency vehicles and thus can easily be eliminated, and those that are similar in design and must be exhaustively compared with the impression with regard to the characteristics of tread design, dimension, wear, and individual characteristics. For those that fall into the category of being of a different design to the questioned impressions, elimination standards need only consist of a digital photograph or adhesive lift of a short segment of the design. In addition, the sidewall brand name and style and size should be noted, as well as what vehicle the tire is associated with. If the tire is similar in design to the questioned impression, the actual tire is required. If the actual vehicle is seized, that vehicle can be used to produce the known standards. If the tires alone are seized from the vehicle, each tire’s position on the vehicle (left front, right rear, etc.) and the side of the tire facing out (white wall side or black wall side) should be noted and should be marked directly on the tire before it is removed from the vehicle. To assist in the comparison process, known full circumference impressions of the tire must be obtained to assist in that comparison process. This is accomplished with inks or powders on long pieces of solid core chart board, or on clear polyester film placed over the chart board. This may be done on the actual suspect vehicle, or on a vehicle which will accommodate the tire. Cases involving large trucks or trailer rigs should utilize those trucks or trailers when obtaining the known impressions. Tires should not be removed from any trucks that have double tires mounted on each side if they are to be compared with double tire impressions from the scene of the crime. Only after adequate known impressions are taken should they be removed for a more detailed examination. This is because the relative position of the tires to one another, as they have been mounted, is highly significant. Removal of the tires would lose that important aspect of the evidence.
Tread-Wear Indicators
Examination of Tire Impressions
Tread-wear indicators, also known as wear bars, are required in tire manufacturing. On tires 13 inch. or larger in diameter, tread-wear indicators must appear at least six times around the tire’s circumference. For tires having a 12-inch. diameter or smaller, there must be at least three tread-wear indicators. They consist of rubber bars which are raised 2/32nds of an inch
Forensic examination first evaluates the general class characteristics of the tread design and dimension. If the tread design of the questioned impression is visibly different from a particular tire, that tire can be eliminated. If the tread design is similar, a more detailed examination must take place and requires full circumference impression standards of that tire. These must be
Direction
Tire center line
Direction
3 2 13 2 1 3 2 13 2 13 2 1
A directional noise treatment has a pitch sequence that is different on each side of the tire; thus, it lays down a different sequence of noise treatment in each direction, relative to its direction of travel. An example of this is illustrated below. An impression made by a tire with directional noise treatment would enable a determination of the direction of the vehicle from the impression, as long as the position of the tire (left or right side of vehicle) and the way the tire was mounted on the wheel (which side is out, which side is in) are known. Directional noise treatment should not be confused with a directional tire, which must be mounted in a prescribed way and whose direction can be visually distinguished. 1 2 31 2 3 1 2 31 2 31 2 3
Direction
Tire center line
Direction
1 2 31 2 3 1 2 31 2 31 2 3
Known Standards of Tires
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
made on a vehicle under load. With the full circumference impressions, the specific tread design and its dimensions, including agreement or disagreement of the noise treatment, can be compared. This examination of the tire will require superimposition of the known impressions over the questioned impression(s). This assists in locating the specific design, size, and noise treatment features, as well as characteristics of wear and individual characteristics. If the design, size, and noise treatment correspond, further comparison of the tire or tires proceeds. Any wear characteristics, such as worn-away tread pattern, sipes, irregular tire wear, and tread-wear indicators, will assist further in locating the possible area or areas of the tire that could potentially have made the crime scene impression. Finally, any randomly acquired individual characteristics such as scratches, tears, cuts, stone holds, and sipe damage that appear on the tires and are clearly evident in the impression are examined. Their presence on the tire is random in nature and results in a tire that differs from others of the same tread dimension and design. The presence of random individual characteristics will contribute toward, or be the basis for, identification of that tire as making the crime scene impression. When making examinations between a crime scene tire impression and a suspect tire, a range of conclusions is possible. It can be concluded that a tire positively made an impression. This would occur when the crime scene impression and suspect tire correspond in design, noise treatment, dimension, condition of wear, and also share sufficient randomly acquired individual features. In less conclusive examinations, it is still often possible to associate a crime scene tire impression as sharing significant features in common with the suspect tire, such as design, noise treatment, dimension, and condition of wear. Because of the large number of possible designs and sizes and conditions of wear, particularly when dealing with replacement tires, this category of conclusion is still valuable and highly relevant. Finally, substantive differences in class characteristics of size or design in the noise treatment or significant differences in the condition of wear can contribute toward, or be the basis for, elimination of the tire. It is noted that the absence of random individual characteristics, either in the crime scene impression or tire, does not constitute a basis for nonidentification for a few reasons. The impression may not have retained sufficient detail to allow for examination of those areas, or sufficient additional mileage on the vehicle may have worn off old characteristics or it may have acquired new characteristics.
5
of the front wheels. The rear tire track measurements will always record in the substrate accurately, whether going straight or while turning, as they are attached to a fixed axle. The front wheel track measurement will only measure accurately if the vehicle is going straight, but will change dramatically if the vehicle is turning as the resulting tracks will be closer together. Consequently, the front track measurement is less reliable. With regard to both front and rear measurements, it should be noted that in substrates that are uneven, or in cases where the impression does not record sufficiently, it becomes more difficult to measure track width accurately. Additionally, if custom wheels of different dimensions have been placed on the vehicle, or if the wheel mounting changes, as in the case of mounting wheels in a reversed position, the track width for that vehicle will be changed from its original specifications. The track width on trucks that have two tires mounted on each side is measured from the point that is the direct center between the two wheels on one side to the center of the two wheels on the opposite side. Should trucks of the same type, model, and year be configured with different axles or different wheels, the track width will be changed. Track width and wheelbase measurements are illustrated in Figure 3.
Wheelbase The wheelbase of a vehicle is the dimension measured longitudinally between the center of the front and rear wheels. A close equivalent to the wheelbase can be measured as the distance between the leading edges of the front and rear tire tracks, as in the case where the tires have sunk in the ground or have turned. Measurements should be taken from each side of the impression, as the leading edge of a tire, when turning, will cause this measurement to increase or decrease, depending on which side of the tire is used for the measurement.
(a)
Vehicle Dimensions and Turning Tread Design Width Tread design width, also known as “arc” width, is the distance between the edges of the tire tread. This is sometimes difficult to measure, owing to uneven wearing of the tire, the incompleteness of some impressions, and other factors.
Track Width (Stance) Track width, also known as “tire stance,” is the distance measured perpendicularly from the center of one wheel, tire, or impression to the opposite wheel, tire, or impression. In most vehicles, the track width of the rear wheels is different from that
(b)
Figure 3 (a) Track width: the dimension measured between the tire and wheel centers. The front and rear track widths for most vehicles are not the same. (b) Wheelbase: the dimension measured longitudinally between the center of the front and rear wheels.
6
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement Turning diameter ¼ ðB2 AÞ þ A
Turning Positions Tires positioned at the rear of a vehicle, when the vehicle is turning, track to the inside of the respective front tires. This is very important to understand when reconstructing the position of tires at a crime scene and later linking similar positions to the respective tires. This is illustrated in Figure 4.
For example, in Figure 5, if line x to x0 equals 9 m, then B equals 4.5 m, and if A equals 3.1 m, then: Turning diameter ¼ ð4:52 3:1Þ þ 3:1 ¼ ð20:25 3:1Þ þ 3:1 ¼ 6:53 þ 3:1 ¼ 9:63m
Turning Diameter Every vehicle has a turning radius or turning diameter that represents the smallest radius that that particular vehicle type can turn in a circle. A crime scene impression with front wheel tracks that turn sharply can be measured and used to include or eliminate vehicles which can or cannot turn in that diameter or less. The measurement of the track should be made at its outer margin. The following formula and Figure 5 illustrate this procedure.
Left rear
Left front
Right rear
Right front
Figure 4 Turning positions. When the vehicle is turning, the rear tires track to the inside of the respective front tires.
x
B
A
B
x⬘
Figure 5 Turning diameter. Measurements are taken from the outer edge of the arc made by the outermost front tire. See text for details.
Recovery Methods Specific to Tires Photography The general crime scene and examination quality photography of tire impressions at the scene of a crime is carried out in the same manner as for footwear marks, with one exception. That exception involves the need sometimes to document a tire impression which is longer than that typically captured in a single examination quality photograph. This normally applies to impressions that are in excess of 0.5 m in length. Impressions longer than 0.5 m require a sequence of overlapping photographs, which upon processing and enlarging can be combined to recreate the long tire impression for comparison. To take sequenced photographs of a long tire impression, a rigid meter stick should be laid alongside the full length of the long impression. The meter stick should be placed so it is on the same level or plane as the bottom of the tire impression. Once laid down and once photography begins, it should not be disturbed. It will not be used as a scale but only to help reconstruct the sequence and later splice the photographs together. A more accurate scale can be positioned on top of the meter stick in each individual tire impression segment photographed and moved accordingly as the sequence of photographs are taken along the length of the long impression. The photograph of each section should be approximately 0.5 m and overlap the previous photography by 6–10 cm. With this method, a long impression can be photographed in several segments, each accurately representing the respective section. The natural size enlargements of the segments can be assembled together to recreate the full impression. This method is illustrated in Figure 6.
Casting Dental stone casts of three-dimensional tire impressions are invaluable for examination and, if properly taken, will provide the most detailed and accurately sized representation of the tire impression. Casts capture the contours and uneven qualities of the tire impressions, which are not always apparent or able to be recovered in photographs. In deeper impressions, sidewall treatments are often recorded, revealing potentially important information. For this reason, the casting material should be allowed to completely fill and overflow out of the tire impression. Because of the noise treatment, it is also desirable to cast the largest tire segment as is reasonably possible. Impressions at crime scenes that are 1 m or less should always be cast in their entirety. Larger casts can be made for longer impressions but as they increase in length, particularly if they are deep, their size and weight will rapidly become unmanageable. In cases
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
7
Figure 6 Documenting a long tire impression photographically.
involving long segments of one or more tire tracks from a vehicle, at least one cast, a minimum of 1 m long if possible, should be made of the best portion of each separate track. Additional casts, particularly of the more detailed segments of the tracks, should be considered, if possible. On the back of the cast, information about each impression and its relative direction should be noted. In addition, general scene photographs should be taken of the casts, once they are all poured but before they are lifted from the scene. This will also document the position and direction of the casts. Tracks made by trucks with dual assemblies, that is, two tires mounted side by side, should be cast as one unit. This will assure that a record of the exact relative position of those tires to each other is made.
crime scene tire impression. Some newer precured processes use a continuous band of tread that is stretched around the tire carcass, eliminating the splice joint. Retread tires for passenger vehicles are not made in the quantities that original molded tires are made. The occurrence of a particular design of a retreaded tire on a vehicle is therefore less frequent and thus more significant. Information to support the production volume of a particular tire can be obtained by contacting the retreading facility, via the retread code on the tire. A retread DOT code, explained earlier, should be present on the retread tire.
See also: Investigations: Preservation; Recording; Recovery of Human Remains.
Retreaded Tires Retreaded tires are predominantly used on medium and large trucks, where the monetary savings between new tires and retreaded tires is significant. Some retread designs for truck tires closely simulate the design of OEM tires. Retreaded tires are made using one of two processes. Each of these processes leaves characteristics that reveal that the tire is a retread and some may also contribute to the individuality of the tire. They are known as the ‘mold cure’ process and the ‘precured’ process. The mold cure process uses strips of raw rubber that are applied to the used tire carcass, which is then placed into a mold where the new tread is formed. The traditional precured process uses premolded rubber containing the tread design, which is then bonded to the original tire carcass and will contain a splice joint, revealing where the precured tread rubber was joined together. The position of this joint will be different from most other retread tires of this design, and will be very significant should evidence of it be retained in a
Further Reading Bodziak WJ (2000) Footwear Impression Evidence: Detection, Recovery and Examination, 2nd edn. Boca Raton, FL: CRC Press. Bodziak WJ (2008) Tire Tread and Tire Track Evidence. Boca Raton, FL: CRC Press. Bodziak WJ (2009) Forensic Tire Tread and Tire Track Evidence. Forensic science: An introduction to scientific and investigative techniques, 3rd edn., ch. 20, pp. 393–406. Boca Raton, FL: CRC Press. McDonald P (1989) Tire Imprint Evidence. Boca Raton, FL: CRC Press. Nause L (1987) The science of tire impression identification. RCMP Gazette 49(1): 1–25. Nause L (2001) Forensic Tire and Vehicle Track Identification. Ottawa: Canadian Police College. Tread Design Guide, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually. Who Makes it and Where, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually. Who Retreads Tires, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually.
Contents Vehicle Tire Marks and Tire Track Measurement Plastic Bag Striations Bare Footprint Marks The Friction Ridge Skin of the Feet Palm Prints Footwear Marks Serial Number Shotgun Ammunition on a Target Physical Match Tools Analysis, Comparison, Evaluation, and Verification (ACE-V)
Vehicle Tire Marks and Tire Track Measurement WJ Bodziak, Bodziak Forensics, Palm Coast, FL, USA ã 2013 Elsevier Ltd. All rights reserved.
Introduction
Sidewall Information
In today’s highly mobile society, criminals often use vehicles to travel to and from the scenes of the crimes they commit. Their vehicles track over surfaces such as sand, soil, and snow, which will often retain the impressions of one or more tires. There are two forms of tire evidence potentially left at the scenes of crime. Tire marks or tire impressions are those left by the tread design. Tire tracks leave dimensional information exclusive of the tread design, and include track width, wheelbase, turning radius, as well as the relative positions of the tracks of all four tires. Tire evidence ranges from a partial impression of one tire to a full set of tracks representing all four tires. Often details produced are sufficient to provide evidence of a vehicle’s presence. Proper recovery of this evidence, through good notes and crime scene drawing measurements, photography, and casting, serves as a way of preserving the evidence for subsequent comparison with the tires and track dimensions of a vehicle. Figure 1 gives some basic nomenclature.
Much information is molded into the sidewall. Portions of that information are of importance to the investigator and examiner, and should be noted when investigating or examining any tire. First noted should be the brand name and style name, such as Michelin XMþS 244 and the size of the tire, such as P 195 75/R 14. Also of importance is the United States Department of Transportation (DOT) number, which will usually begin with the letters DOT. Because of the worldwide tire market, this information will be found on tires made in any country. The DOT information is now required to be on both sidewalls. The DOT number will be similar to the following example:
Encyclopedia of Forensic Sciences, Second Edition
DOT Department of transportation
HM
L9
Manufacturer Size code and plant code Michelin Tire Stoke-on-Trent, England
ABCD
4911
Optional symbols for manufacturer
Date of manufacturer 49th week of 2011
In this example, the two letters following the DOT number, such as HM, are symbols for the manufacturer and plant code. By
http://dx.doi.org/10.1016/B978-0-12-382165-2.00273-7
1
2
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
Groove Rib
Center line Sipe
Design element Slot or lateral groove Lug
Tread surface
Tread wear indicator (wear bar)
Belts Radial plies Inner liner White sidewall (a)
Bead wire
(b)
Bead wrap
Figure 1 (a) and (b) Radial tire: basic terminology.
looking this code up in a reference source, such as who makes it and where, or searching the Internet for ‘tire plant code HM,’ the specific plant in this example can be identified as the Michelin Tire Company, located in Stoke-on-Trent, England. The next letter and number are the tire size code. The following four letters, for example, ABCD, are optional and are the manufacturer’s symbols. The last four numerical digits are important, as they indicate the week and year in which the tire was manufactured. For example, the numbers 4911 in this example would indicate the tire was made in the 49th week (49) of 2011 (11). Tires made prior to the year 2000 only had three numbers, thus a number here of ‘491’ would indicate the 49th week of 1991. Retreaded tires have a slightly different DOT number on them. The retread DOT number will begin with the letters DOTR or perhaps just R. The original DOT number that was on the new tire should still be present, so it is likely that a retreaded tire will have both a DOT and a DOTR number on it. The DOTR number consists of three letters and three numbers and would be similar to the following example:
In this example, the three letters are a code to identify the retreading facility. A publication, Who Retreads Tires, lists approximately 5000 retreading facilities by their three-letter code. The four numbers identify the week and year of retreading.
will have its plies running at a bias angle across the tire. A biasbelted tire will have the same plies, but will have the addition of a belt beneath the tread area. While bias and bias-belted tires were predominant many years ago, only some large truck tires and tires for large construction equipment will likely be found to still have bias construction. Bias and bias-belted tires are less effective at reducing tire squirm, that is, the degree of contraction of the tire tread while under load. Thus, the impression left by a bias or bias-belted tire may appear to have a narrower appearance than what appears on the tire itself. A radial tire will have the plies running in a radial direction, from bead to bead. Radial tires, because of the radial direction of their plies, reduce the amount of squirm, and result in almost no difference in dimension. In an examination, test impressions of the tire made while under load on a vehicle are necessary to provide a comparable dimensional standard for comparison with a crime scene impression. Tires are built of many components, including a liner, sidewall components, the bead, plies, belts, and tread rubber. These are assembled on a rotating and collapsible drum. After assembly of the components, the ‘green tire,’ whose tread rubber contains no tread or sidewall design at this point, is transferred to a mold. In the mold, under extreme heat and pressure, the various tire components will be vulcanized and bonded together. A steampressured bladder will inflate inside the tire and press the green tire against the surfaces of the mold. It is here that the tread and sidewall designs will be molded into the rubber.
Tire Construction
Tire Designs and Databases
There are three basic types of tire construction that have been used in tire building: bias, bias-belted, and radial. A bias tire
There are thousands of designs of tires, including those made for passenger vehicles; light, medium, and heavy trucks;
DOTR
YPY
1211
Retreated tire
Goodyear Retread Frederickton, NB Canada
12th week of 2011
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
agricultural vehicles; off-the-road vehicles; and motorcycles. Since the 1960s, the Tread Design Guide® (Tire Guides Inc., Boca Raton, FL, USA) has offered a listing and photographs of most tire designs. This guide is published annually in hard copy form and up through 2010, a more comprehensive version on a CD-ROM known as Tread Assistant, which included over 18 000 tire designs, was produced. The CD version was discontinued with the year 2011. The CD version was subdivided by the type of tire category, that is, ribbed tire, metric, lugged tire, and so on, allowing for easier search on a PC computer format. In recent years, a new database known as TreadMate® (Foster & Freeman Ltd, Vale Park, Evesham, Worcestershire, WR11 1TD, UK) has been launched. These sources provide the investigator a method of linking a crime scene impression to a specific tire design and manufacturer. Once done, additional information of relevance can be sought from the respective manufacturer if needed.
Original Equipment Tires Versus Replacement Tires Original equipment manufacturer (OEM) tires, usually referred to as just ‘OE’ tires, are those which are put on a vehicle when it is manufactured. Replacement tires are those which are purchased to replace the OE tires, or other replacement tires, when they wear out. A particular vehicle with its four OE tires will not be a rare occurrence, as many thousands of those vehicles would have been sold with the same design and size of OE equipment. On the other hand, a vehicle with one or more replacement tires on it constitutes a much less frequent occurrence, as other vehicles of that type and brand are less likely to have the same combination of brand and style replacement tires. A vehicle with three or four different designs of replacement tires in a particular size constitutes a rare occurrence that would probably not be repeated, owing to the large number of available designs and sizes.
flatter and proportionally wider, whereas a tire with a higher profile, such as 70, appears more conventional. Today, an increasing number of passenger cars are equipped with lowprofile tires to increase traction and performance.
Noise Treatment Tires produce noise for many reasons. Noise is generated differently as a tire crosses different surfaces, such as from asphalt to concrete. Noise is also generated as air is trapped in the void areas of the tread design upon impact with the substrate, creating a noise when it escapes. In addition, the individual tread blocks will vibrate, creating noise notable at higher speeds. Manufacturers attempt to treat and reduce this category of ‘noise’ by varying the pitch, or size, of the tread blocks as they are positioned around the tire. The sounds emitted by varied pitches create better harmonics than the sounds emitted by the same pitch repetitively. The industry refers to this as ‘noise treatment.’ Noise treatment originally involved creating three sizes of tread blocks (design elements), that is, s, m, and l (or 1, 2, and 3). In some cases, the tread blocks may follow a 1,2,3,1,2,3,1,2,3,. . . arrangement around the tire. Or, they may have an arrangement of those same three sizes, but in a more random order, such as 1,3,2,2,3,1,2,3,1,1,2,3,3,2,2,1 and so forth. In other cases, more complex and varied arrangements, including more than just three different sizes, may involve a pattern such as 1,2,3,4,4,3,2,1, 3,3,2,2,2,2,3,3,4,3,2,1,1,2,3,4, and so forth. An example of such an arrangement is illustrated in Figure 2. In this example, the noise treatment consists of 64 design elements of four different sizes. They are arranged in four
A B C D
12344321 4321 1234 22 33 33 22 33 2222 33
D A
4
3
3 3 2 2 2 2 3 21 3
4
4
Tire Size Designations
3 2
1
32112 3 4 2 4 32
1
2 3 4 4 3 2 4 1 1 23 2
1/
th
3
3
6
3
3
2 32
2
2
1 2 3 4 43 2 1
The aspect ratio, otherwise known as the tire profile, is the relation of the height of a tire to its width. The appearance of a tire with a low profile or aspect ratio, such as 45, will look
3
Aspect Ratio
3
Metric: 195R14; 195, approximate section width in millimeters; R, radial tire; 14, rim diameter; P-Metric, P 195/75 R 14; P, passenger tire; 195, approximate section width in millimeters; 75, aspect ratio; R, radial tire; 14, rim diameter.
2
C
Newer Designations
B
1
B
Numeric: 6.45–14; 6.45, approximate section width in inches; 14, rim diameter; Alphanumeric: E R 78–14; E, load/size relationship; R, radial tire; 78, aspect ratio; 14, rim diameter.
3
2
Tire sizes have been designated in a number of ways throughout the years. The tire size designations that have been used are shown below.
Older Designations
3
C
A
4 3
3 2 1 1 4
4
2 3
3
2 2 3 3
2 1 3 3 2 2
Tire impressions
Figure 2 Noise treatment example.
A
4
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
sequences, represented by models A, B, C, and D. The six treadwear indicators are also included in Figure 2. The lower part of the figure represents a crime scene impression. Note that only one possible area of the tire could have produced the noise treatment in that impression. This is because the portion of noise treatment for model A plus the portion of model D, as shown in Figure 2, does not repeat elsewhere in the tire. Tires were originally produced with a nondirectional noise treatment, that is, the pitch sequence was identical on both sides of the tire as shown below. With this form of noise treatment, the tire will leave an identical repeating sequence in either direction. Examination of a crime scene impression made by a tire with nondirectional noise treatment would not enable determination of the direction of the vehicle based on this alone.
(0.16 cm) above the base of the grooves. In this way, as the tire wears down, the wear indicators will appear as bald strips across the remaining tread design. Tread-wear indicators are visible in a two-dimensional impression only if the tire is worn down to that level. They may be visible in three-dimensional impressions if the tire had produced a deep enough impression in the substrate. Tread-wear indicators will occur in different portions relative to the noise treatment of that tire. Each tread-wear indicator will therefore be in a different portion of the noise treatment arrangement (Figure 2). This can be of further assistance in locating the precise portion of the tire that made the impression.
1 2 31 2 3 1 2 31 2 31 2 3
The noise treatment of tires is used whenever possible during the examination of tire impressions, as it assists in locating the possible position on the tire that could have made a particular impression. An average passenger or light truck tire may have 2 m or more of tread in a full circumference impression. A crime scene photograph or a cast of a tire impression may only be 0.25–0.5 m in length. If it is of sufficient length, the crime scene impression will only match one location around the circumference of the tire that made it. Once that position is located, it will then be additionally examined for evidence of wear and acquired individual characteristics. Recovering longer segments of impressions at crime scenes allows for a more specific determination of the portion(s) of the tire that made the impression. Every examiner who conducts forensic tire impression examinations should be knowledgeable about tread design noise treatment and how it is significant in the comparison process.
Known standards of tires fall into two different categories. They include those obtained for tires that differ in design from the questioned impression such as police and emergency vehicles and thus can easily be eliminated, and those that are similar in design and must be exhaustively compared with the impression with regard to the characteristics of tread design, dimension, wear, and individual characteristics. For those that fall into the category of being of a different design to the questioned impressions, elimination standards need only consist of a digital photograph or adhesive lift of a short segment of the design. In addition, the sidewall brand name and style and size should be noted, as well as what vehicle the tire is associated with. If the tire is similar in design to the questioned impression, the actual tire is required. If the actual vehicle is seized, that vehicle can be used to produce the known standards. If the tires alone are seized from the vehicle, each tire’s position on the vehicle (left front, right rear, etc.) and the side of the tire facing out (white wall side or black wall side) should be noted and should be marked directly on the tire before it is removed from the vehicle. To assist in the comparison process, known full circumference impressions of the tire must be obtained to assist in that comparison process. This is accomplished with inks or powders on long pieces of solid core chart board, or on clear polyester film placed over the chart board. This may be done on the actual suspect vehicle, or on a vehicle which will accommodate the tire. Cases involving large trucks or trailer rigs should utilize those trucks or trailers when obtaining the known impressions. Tires should not be removed from any trucks that have double tires mounted on each side if they are to be compared with double tire impressions from the scene of the crime. Only after adequate known impressions are taken should they be removed for a more detailed examination. This is because the relative position of the tires to one another, as they have been mounted, is highly significant. Removal of the tires would lose that important aspect of the evidence.
Tread-Wear Indicators
Examination of Tire Impressions
Tread-wear indicators, also known as wear bars, are required in tire manufacturing. On tires 13 inch. or larger in diameter, tread-wear indicators must appear at least six times around the tire’s circumference. For tires having a 12-inch. diameter or smaller, there must be at least three tread-wear indicators. They consist of rubber bars which are raised 2/32nds of an inch
Forensic examination first evaluates the general class characteristics of the tread design and dimension. If the tread design of the questioned impression is visibly different from a particular tire, that tire can be eliminated. If the tread design is similar, a more detailed examination must take place and requires full circumference impression standards of that tire. These must be
Direction
Tire center line
Direction
3 2 13 2 1 3 2 13 2 13 2 1
A directional noise treatment has a pitch sequence that is different on each side of the tire; thus, it lays down a different sequence of noise treatment in each direction, relative to its direction of travel. An example of this is illustrated below. An impression made by a tire with directional noise treatment would enable a determination of the direction of the vehicle from the impression, as long as the position of the tire (left or right side of vehicle) and the way the tire was mounted on the wheel (which side is out, which side is in) are known. Directional noise treatment should not be confused with a directional tire, which must be mounted in a prescribed way and whose direction can be visually distinguished. 1 2 31 2 3 1 2 31 2 31 2 3
Direction
Tire center line
Direction
1 2 31 2 3 1 2 31 2 31 2 3
Known Standards of Tires
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
made on a vehicle under load. With the full circumference impressions, the specific tread design and its dimensions, including agreement or disagreement of the noise treatment, can be compared. This examination of the tire will require superimposition of the known impressions over the questioned impression(s). This assists in locating the specific design, size, and noise treatment features, as well as characteristics of wear and individual characteristics. If the design, size, and noise treatment correspond, further comparison of the tire or tires proceeds. Any wear characteristics, such as worn-away tread pattern, sipes, irregular tire wear, and tread-wear indicators, will assist further in locating the possible area or areas of the tire that could potentially have made the crime scene impression. Finally, any randomly acquired individual characteristics such as scratches, tears, cuts, stone holds, and sipe damage that appear on the tires and are clearly evident in the impression are examined. Their presence on the tire is random in nature and results in a tire that differs from others of the same tread dimension and design. The presence of random individual characteristics will contribute toward, or be the basis for, identification of that tire as making the crime scene impression. When making examinations between a crime scene tire impression and a suspect tire, a range of conclusions is possible. It can be concluded that a tire positively made an impression. This would occur when the crime scene impression and suspect tire correspond in design, noise treatment, dimension, condition of wear, and also share sufficient randomly acquired individual features. In less conclusive examinations, it is still often possible to associate a crime scene tire impression as sharing significant features in common with the suspect tire, such as design, noise treatment, dimension, and condition of wear. Because of the large number of possible designs and sizes and conditions of wear, particularly when dealing with replacement tires, this category of conclusion is still valuable and highly relevant. Finally, substantive differences in class characteristics of size or design in the noise treatment or significant differences in the condition of wear can contribute toward, or be the basis for, elimination of the tire. It is noted that the absence of random individual characteristics, either in the crime scene impression or tire, does not constitute a basis for nonidentification for a few reasons. The impression may not have retained sufficient detail to allow for examination of those areas, or sufficient additional mileage on the vehicle may have worn off old characteristics or it may have acquired new characteristics.
5
of the front wheels. The rear tire track measurements will always record in the substrate accurately, whether going straight or while turning, as they are attached to a fixed axle. The front wheel track measurement will only measure accurately if the vehicle is going straight, but will change dramatically if the vehicle is turning as the resulting tracks will be closer together. Consequently, the front track measurement is less reliable. With regard to both front and rear measurements, it should be noted that in substrates that are uneven, or in cases where the impression does not record sufficiently, it becomes more difficult to measure track width accurately. Additionally, if custom wheels of different dimensions have been placed on the vehicle, or if the wheel mounting changes, as in the case of mounting wheels in a reversed position, the track width for that vehicle will be changed from its original specifications. The track width on trucks that have two tires mounted on each side is measured from the point that is the direct center between the two wheels on one side to the center of the two wheels on the opposite side. Should trucks of the same type, model, and year be configured with different axles or different wheels, the track width will be changed. Track width and wheelbase measurements are illustrated in Figure 3.
Wheelbase The wheelbase of a vehicle is the dimension measured longitudinally between the center of the front and rear wheels. A close equivalent to the wheelbase can be measured as the distance between the leading edges of the front and rear tire tracks, as in the case where the tires have sunk in the ground or have turned. Measurements should be taken from each side of the impression, as the leading edge of a tire, when turning, will cause this measurement to increase or decrease, depending on which side of the tire is used for the measurement.
(a)
Vehicle Dimensions and Turning Tread Design Width Tread design width, also known as “arc” width, is the distance between the edges of the tire tread. This is sometimes difficult to measure, owing to uneven wearing of the tire, the incompleteness of some impressions, and other factors.
Track Width (Stance) Track width, also known as “tire stance,” is the distance measured perpendicularly from the center of one wheel, tire, or impression to the opposite wheel, tire, or impression. In most vehicles, the track width of the rear wheels is different from that
(b)
Figure 3 (a) Track width: the dimension measured between the tire and wheel centers. The front and rear track widths for most vehicles are not the same. (b) Wheelbase: the dimension measured longitudinally between the center of the front and rear wheels.
6
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement Turning diameter ¼ ðB2 AÞ þ A
Turning Positions Tires positioned at the rear of a vehicle, when the vehicle is turning, track to the inside of the respective front tires. This is very important to understand when reconstructing the position of tires at a crime scene and later linking similar positions to the respective tires. This is illustrated in Figure 4.
For example, in Figure 5, if line x to x0 equals 9 m, then B equals 4.5 m, and if A equals 3.1 m, then: Turning diameter ¼ ð4:52 3:1Þ þ 3:1 ¼ ð20:25 3:1Þ þ 3:1 ¼ 6:53 þ 3:1 ¼ 9:63m
Turning Diameter Every vehicle has a turning radius or turning diameter that represents the smallest radius that that particular vehicle type can turn in a circle. A crime scene impression with front wheel tracks that turn sharply can be measured and used to include or eliminate vehicles which can or cannot turn in that diameter or less. The measurement of the track should be made at its outer margin. The following formula and Figure 5 illustrate this procedure.
Left rear
Left front
Right rear
Right front
Figure 4 Turning positions. When the vehicle is turning, the rear tires track to the inside of the respective front tires.
x
B
A
B
x⬘
Figure 5 Turning diameter. Measurements are taken from the outer edge of the arc made by the outermost front tire. See text for details.
Recovery Methods Specific to Tires Photography The general crime scene and examination quality photography of tire impressions at the scene of a crime is carried out in the same manner as for footwear marks, with one exception. That exception involves the need sometimes to document a tire impression which is longer than that typically captured in a single examination quality photograph. This normally applies to impressions that are in excess of 0.5 m in length. Impressions longer than 0.5 m require a sequence of overlapping photographs, which upon processing and enlarging can be combined to recreate the long tire impression for comparison. To take sequenced photographs of a long tire impression, a rigid meter stick should be laid alongside the full length of the long impression. The meter stick should be placed so it is on the same level or plane as the bottom of the tire impression. Once laid down and once photography begins, it should not be disturbed. It will not be used as a scale but only to help reconstruct the sequence and later splice the photographs together. A more accurate scale can be positioned on top of the meter stick in each individual tire impression segment photographed and moved accordingly as the sequence of photographs are taken along the length of the long impression. The photograph of each section should be approximately 0.5 m and overlap the previous photography by 6–10 cm. With this method, a long impression can be photographed in several segments, each accurately representing the respective section. The natural size enlargements of the segments can be assembled together to recreate the full impression. This method is illustrated in Figure 6.
Casting Dental stone casts of three-dimensional tire impressions are invaluable for examination and, if properly taken, will provide the most detailed and accurately sized representation of the tire impression. Casts capture the contours and uneven qualities of the tire impressions, which are not always apparent or able to be recovered in photographs. In deeper impressions, sidewall treatments are often recorded, revealing potentially important information. For this reason, the casting material should be allowed to completely fill and overflow out of the tire impression. Because of the noise treatment, it is also desirable to cast the largest tire segment as is reasonably possible. Impressions at crime scenes that are 1 m or less should always be cast in their entirety. Larger casts can be made for longer impressions but as they increase in length, particularly if they are deep, their size and weight will rapidly become unmanageable. In cases
Pattern Evidence | Vehicle Tire Marks and Tire Track Measurement
7
Figure 6 Documenting a long tire impression photographically.
involving long segments of one or more tire tracks from a vehicle, at least one cast, a minimum of 1 m long if possible, should be made of the best portion of each separate track. Additional casts, particularly of the more detailed segments of the tracks, should be considered, if possible. On the back of the cast, information about each impression and its relative direction should be noted. In addition, general scene photographs should be taken of the casts, once they are all poured but before they are lifted from the scene. This will also document the position and direction of the casts. Tracks made by trucks with dual assemblies, that is, two tires mounted side by side, should be cast as one unit. This will assure that a record of the exact relative position of those tires to each other is made.
crime scene tire impression. Some newer precured processes use a continuous band of tread that is stretched around the tire carcass, eliminating the splice joint. Retread tires for passenger vehicles are not made in the quantities that original molded tires are made. The occurrence of a particular design of a retreaded tire on a vehicle is therefore less frequent and thus more significant. Information to support the production volume of a particular tire can be obtained by contacting the retreading facility, via the retread code on the tire. A retread DOT code, explained earlier, should be present on the retread tire.
See also: Investigations: Preservation; Recording; Recovery of Human Remains.
Retreaded Tires Retreaded tires are predominantly used on medium and large trucks, where the monetary savings between new tires and retreaded tires is significant. Some retread designs for truck tires closely simulate the design of OEM tires. Retreaded tires are made using one of two processes. Each of these processes leaves characteristics that reveal that the tire is a retread and some may also contribute to the individuality of the tire. They are known as the ‘mold cure’ process and the ‘precured’ process. The mold cure process uses strips of raw rubber that are applied to the used tire carcass, which is then placed into a mold where the new tread is formed. The traditional precured process uses premolded rubber containing the tread design, which is then bonded to the original tire carcass and will contain a splice joint, revealing where the precured tread rubber was joined together. The position of this joint will be different from most other retread tires of this design, and will be very significant should evidence of it be retained in a
Further Reading Bodziak WJ (2000) Footwear Impression Evidence: Detection, Recovery and Examination, 2nd edn. Boca Raton, FL: CRC Press. Bodziak WJ (2008) Tire Tread and Tire Track Evidence. Boca Raton, FL: CRC Press. Bodziak WJ (2009) Forensic Tire Tread and Tire Track Evidence. Forensic science: An introduction to scientific and investigative techniques, 3rd edn., ch. 20, pp. 393–406. Boca Raton, FL: CRC Press. McDonald P (1989) Tire Imprint Evidence. Boca Raton, FL: CRC Press. Nause L (1987) The science of tire impression identification. RCMP Gazette 49(1): 1–25. Nause L (2001) Forensic Tire and Vehicle Track Identification. Ottawa: Canadian Police College. Tread Design Guide, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually. Who Makes it and Where, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually. Who Retreads Tires, pp. 1101–1106. S. Rogers Circle, Boca Raton, FL: Tire Guides Inc., published annually.