CASE 012
:
THE CASE OF THE MIDNIGHT COLLISION
12:17 AM. A rural intersection. Two cars. No witnesses. Both drivers insist they had the right of way — and the camera missed the moment of impact. The wreckage, the tyre marks, and the data recorded in the final seconds before impact are the only witnesses left. But witnesses can be misread.
CASE BRIEFING
The call came in at 12:19 AM.
A two-vehicle collision at the intersection of Harwick Lane and Millfield Road — a rural four-way junction six kilometres outside Millhaven. No traffic signals. A standard give-way arrangement. No street lighting beyond a single lamp post at the northwestern corner.
When the first patrol car arrived at 12:31 AM both vehicles were stationary. Both drivers were conscious.
James Okafor, 34, a warehouse supervisor — had been driving westbound on Harwick Lane in a silver Honda Civic. His vehicle had come to rest on the northern side of the intersection — partially on the grass verge of Millfield Road, facing northwest. The front passenger side showed significant impact damage.
Caroline Mercer, 52, a secondary school administrator — had been driving northbound on Millfield Road in a dark blue Volvo estate. Her vehicle had come to rest in the centre of the intersection, facing slightly northeast. The front driver side showed significant impact damage.
Both drivers were examined by paramedics. James Okafor had a laceration to his forehead and a suspected fractured wrist. Caroline Mercer had bruising to her chest from the seatbelt and a suspected concussion.
A roadside breath test was administered to both drivers as standard procedure.
Caroline Mercer: 0.00 — no alcohol detected.
James Okafor: 0.04 — below the legal limit of 0.08 but above zero.
The attending officer noted the reading in his report.
Both drivers were interviewed at the scene.
James Okafor: "I was travelling west on Harwick Lane. I approached the junction, checked both ways, and entered. I had priority — Millfield Road gives way to Harwick Lane at this junction. She came from my right at speed. I didn't even have time to brake properly before she hit me."
Caroline Mercer: "I entered the intersection first — I was already through the give-way line when he appeared. He was going too fast. He crossed into my path and hit me. I barely had time to react."
The attending officer examined the wreckage positions.
James Okafor's silver Civic had come to rest on the northern side of the intersection — on the Millfield Road verge. That is the side from which Caroline Mercer had been approaching northbound.
To the officer the conclusion appeared straightforward. If James Okafor had been travelling westbound on Harwick Lane his vehicle should have come to rest further west — not on the northern verge. Its position on the northern side suggested it had been travelling northbound — from the direction James Okafor claimed Caroline Mercer had come from.
At 2:15 AM the attending officer filed a preliminary report attributing probable cause to James Okafor — citing the wreckage position, the inconsistency between his stated direction of travel and his vehicle's final resting position, and the above-zero alcohol reading.
James Okafor was issued a notice of intended prosecution for careless driving.
He called his sister from the hospital at 4:00 AM.
"They're saying it was my fault," he said. "But I know what happened. I know where I was. The car ended up there because she hit me. Doesn't anyone understand how physics works?"
The Road Traffic Investigation Unit received the case file the following morning.
Lead investigator DC Priya Nair read the preliminary report, looked at the scene photographs, and noted one thing that the attending officer had not mentioned.
The intersection had a traffic camera — mounted on the lamp post at the northwestern corner. The camera had been recording. Heavy rain had obscured the lens at the moment of impact — but the footage from the ten seconds before impact was intact.
She requested the footage immediately.
She also requested the Event Data Recorders from both vehicles.
"The wreckage tells you where things ended up," she said. "Physics tells you how they got there. Those are not the same thing."
Your investigation begins now.
A rural intersection at midnight. Two drivers with contradictory accounts. A camera that missed the critical moment. A preliminary conclusion that appears supported by the evidence — until you examine the physics of what actually happens to vehicles when they collide.
Examine all five Evidence Files. The tyre marks, the Event Data Recorders, the impact geometry, the camera footage, and the vector reconstruction all have something to say.
The wreckage positions are not where the police think they are from. The physics will show you where they actually came from — and who is telling the truth.
Instructions:
Play solo or with a team of up to 5 investigators. Examine the five Evidence Files together, or divide them among your team and have each investigator analyze different clues. Share what you discover, compare theories, and decide which evidence matters most.
When you've examined all the evidence, work individually or as a team to reach your final verdict—then reveal the solution to see if you cracked the case.
EVIDENCE FILES
EVIDENCE FILE 01 +
EVIDENCE FILE 01 — SCENE EXAMINATION AND TYRE MARK ANALYSIS
Case Reference: MRTI-2024-0914
Evidence Item: EV-01 — Road surface examination and scene measurements
Prepared By: DC Priya Nair, Road Traffic Investigation Unit
Date: Thursday — 9:00 AM
BACKGROUND
Tyre marks on a road surface preserve physical evidence of a vehicle's braking behaviour and position in the moments before a collision. DC Nair attended the scene at first light to examine and record all available tyre marks before weather degraded them further.
The intersection of Harwick Lane and Millfield Road is a standard rural four-way junction. Harwick Lane runs east-west. Millfield Road runs north-south. Give-way markings on Millfield Road require northbound and southbound traffic to yield to eastbound and westbound traffic on Harwick Lane.
Under the give-way arrangement — James Okafor travelling westbound on Harwick Lane had priority. Caroline Mercer travelling northbound on Millfield Road was required to give way.
TYRE MARKS — JAMES OKAFOR — SILVER HONDA CIVIC
A set of tyre marks consistent with the Civic's tyre width was identified on Harwick Lane approaching the intersection from the east.
Mark length: 11.3 metres
Character: moderate braking — consistent with a driver reacting to an unexpected hazard rather than pre-emptive braking
Direction: westbound — consistent with James Okafor's stated direction of travel
Position: centred in the westbound lane of Harwick Lane — no deviation toward the centre line prior to the intersection
The marks end approximately 2 metres east of the intersection centre point — consistent with the vehicle entering the intersection before coming to a complete stop.
TYRE MARKS — CAROLINE MERCER — DARK BLUE VOLVO ESTATE
A set of tyre marks consistent with the Volvo's tyre width was identified on Millfield Road approaching the intersection from the south.
Mark length: 4.1 metres
Character: heavy braking — deeper impression at the start, consistent with sudden emergency braking
Direction: northbound — consistent with Caroline Mercer's stated direction of travel
Position: centred in the northbound lane of Millfield Road
The marks begin approximately 3.8 metres south of the give-way line — meaning Caroline Mercer began braking before reaching the give-way line but very close to it.
WHAT THE TYRE MARKS ESTABLISH — AND WHAT THEY DO NOT
The two sets of marks differ significantly in length.
James Okafor's marks: 11.3 metres — braking began well before the intersection
Caroline Mercer's marks: 4.1 metres — braking began very close to the give-way line
Longer marks indicate earlier brake application relative to the intersection — not necessarily higher speed. The standard skid mark formula can estimate approach speed when a vehicle brakes to a complete stop. In this case neither vehicle stopped — both were still moving at the moment of impact. The formula therefore cannot reliably establish approach speeds from the marks alone.
What the marks do establish:
James Okafor began braking approximately 11.3 metres before the impact point — well before the intersection.
Caroline Mercer began braking approximately 4.1 metres before the impact point — very close to the give-way line and significantly later relative to the intersection than James Okafor.
The marks establish the timing and position of braking relative to the intersection — not approach speeds. Entry speeds will be established more reliably by the Event Data Recorder analysis in Evidence File 02.
WRECKAGE POSITIONS
James Okafor's silver Civic: final resting position on the northern grass verge — facing northwest
Caroline Mercer's dark blue Volvo: final resting position in the centre of the intersection — facing slightly northeast
The Civic's final position on the northern verge was the basis for the attending officer's preliminary conclusion — attributing probable cause to James Okafor.
VEHICLE MASSES — RELEVANT DETAIL
Vehicle mass is a matter of public record from manufacturer specifications.
James Okafor's Honda Civic: 1,200 kilograms
Caroline Mercer's Volvo Estate: 1,800 kilograms
The Volvo is 50% heavier than the Civic.
YOUR TASK
The tyre mark analysis has established the braking positions and directions of both vehicles — both consistent with their stated directions of travel. James Okafor began braking significantly earlier and further from the intersection than Caroline Mercer.
But consider the wreckage positions carefully before drawing conclusions.
James Okafor's Civic ended up on the northern verge — the side from which Caroline Mercer was approaching. The attending officer concluded this meant the Civic had been travelling northbound.
Is that the only explanation — or could a westbound vehicle end up on the northern verge after being struck from the right by a heavier northbound vehicle? Research what happens to vehicles of different masses during a collision — and consider what the 600 kilogram mass difference between the Civic and the Volvo tells you about momentum transfer.
The tyre marks tell you where each vehicle was braking and in what direction. The Event Data Recorder in Evidence File 02 will tell you how fast they were going — and what that means for the collision that followed.
EVIDENCE FILE 02 +
EVIDENCE FILE 02 — EVENT DATA RECORDER ANALYSIS
Case Reference: MRTI-2024-0914
Evidence Item: EV-02 — Vehicle EDR data extraction and analysis
Prepared By: DC Priya Nair, Road Traffic Investigation Unit
Date: Thursday — 2:00 PM
BACKGROUND
Modern vehicles are equipped with an Event Data Recorder — EDR — sometimes called a black box. Similar in principle to an aircraft flight data recorder the EDR continuously overwrites its memory but permanently saves the final 5 seconds of data before and during a collision trigger event.
Saved parameters typically include vehicle speed, brake application, throttle position, steering input, and seatbelt status.
EDRs from both vehicles were extracted and analysed by a specialist technician under DC Nair's supervision.
JAMES OKAFOR — SILVER HONDA CIVIC
Data recorded in the 5 seconds before collision trigger:
T-5 seconds: Speed 34 mph — travelling westbound — throttle at 12% — no brake application
T-4 seconds: Speed 33 mph — throttle reducing to 0%
T-3 seconds: Speed 31 mph — brake application begins — 40% pressure
T-2 seconds: Speed 27 mph — brake pressure increasing to 85%
T-1 second: Speed 22 mph — full brake application
T-0 — collision trigger: Speed 19 mph
Steering input: minor correction to the left in the final 1.5 seconds — consistent with a driver attempting to avoid a vehicle approaching from the right.
Seatbelt: fastened throughout.
CAROLINE MERCER — DARK BLUE VOLVO ESTATE
Data recorded in the 5 seconds before collision trigger:
T-5 seconds: Speed 48 mph — travelling northbound — throttle at 34%
T-4 seconds: Speed 47 mph — throttle at 28%
T-3 seconds: Speed 46 mph — throttle reducing to 0%
T-2 seconds: Speed 43 mph — brake application begins — 60% pressure
T-1 second: Speed 38 mph — brake pressure increasing to 95%
T-0 — collision trigger: Speed 34 mph
Steering input: no steering correction recorded in the final 5 seconds.
Seatbelt: fastened throughout.
KEY FINDINGS
Finding 1 — Speed discrepancy:
Caroline Mercer's EDR recorded a speed of 48 mph at T-5 seconds — 18 mph above the 30 mph speed limit on Millfield Road.
James Okafor's EDR recorded a speed of 34 mph at T-5 seconds — 4 mph above the speed limit on Harwick Lane — reducing progressively as he braked.
Finding 2 — Braking timeline:
James Okafor began reducing throttle at T-4 seconds and applied brakes at T-3 seconds — consistent with his tyre marks beginning 11.3 metres from the intersection.
Caroline Mercer began reducing throttle at T-3 seconds and applied brakes at T-2 seconds — consistent with her tyre marks beginning only 4.1 metres from the give-way line.
Finding 3 — Collision speeds:
James Okafor entered the collision at 19 mph.
Caroline Mercer entered the collision at 34 mph.
TYRE MARK RECONCILIATION
The EDR speeds at the point of braking allow reconciliation with the tyre mark lengths from Evidence File 01.
James Okafor began braking at approximately 31 mph — producing 11.3 metre marks on wet tarmac. Consistent with EDR data.
Caroline Mercer began braking at approximately 43 mph — but her tyre marks measured only 4.1 metres. This is consistent with braking from 43 mph with only 4.1 metres available before impact — she began braking very late, very close to the give-way line, from a significantly higher speed than the tyre marks alone suggested.
YOUR TASK
The EDR data has established two significant findings that the tyre mark analysis alone could not reveal.
Caroline Mercer was travelling at 48 mph in a 30 mph zone in the seconds before the collision — nearly 60% above the speed limit.
James Okafor was travelling at 34 mph — 4 mph above the limit — and had been progressively braking for 3 seconds before impact.
Consider what the speed differential means for the collision dynamics. Caroline Mercer's Volvo — 1,800 kilograms at 34 mph at impact — carried significantly more momentum into the collision than James Okafor's Civic — 1,200 kilograms at 19 mph.
Research the formula for momentum — mass multiplied by velocity. Calculate the momentum of each vehicle at the moment of impact and consider what the momentum difference tells you about which vehicle would push the other — and in which direction.
Does the momentum analysis begin to explain where James Okafor's Civic ended up — and how it got there?
EVIDENCE FILE 03 +
EVIDENCE FILE 03 — IMPACT GEOMETRY AND CRUSH ANALYSIS
Case Reference: MRTI-2024-0914
Evidence Item: EV-03 — Vehicle damage examination and impact angle analysis
Prepared By: Dr. Peter Osei, Collision Reconstruction Specialist
Date: Friday — 10:00 AM
BACKGROUND
When two vehicles collide the damage patterns on each vehicle record the geometry of the impact — the angle at which they met, the direction of the force applied, and which vehicle struck which surface. Dr. Osei examined both vehicles at the secure compound where they had been recovered following the accident.
JAMES OKAFOR — SILVER HONDA CIVIC
Primary damage zone: Front passenger side — the right side of the vehicle from the driver's perspective.
The impact damage is concentrated on the right front quarter — from the front bumper to the B-pillar — the structural post between the front and rear doors.
Crush depth: Maximum crush of 38 centimetres at the right front wheel arch — reducing to 12 centimetres at the B-pillar.
Force direction: Analysis of the crush pattern indicates the primary force was applied from the right side — at an angle of approximately 85 degrees to the Civic's direction of travel.
In plain terms — the Civic was struck almost perpendicularly on its right side by something travelling at close to a right angle to it.
Undercarriage: The right front suspension and wheel assembly show upward and leftward deformation — consistent with a heavy object striking the right side and pushing the vehicle upward and to the left at the point of contact before the vehicle rotated.
CAROLINE MERCER — DARK BLUE VOLVO ESTATE
Primary damage zone: Front of the vehicle — centred slightly left of the centreline — the driver's side front.
The impact damage is concentrated on the left front quarter — from the front bumper to the A-pillar — the structural post beside the windscreen.
Crush depth: Maximum crush of 52 centimetres at the left front corner — reducing to 18 centimetres toward the centre of the bumper.
Force direction: Analysis of the crush pattern indicates the primary force was applied from ahead and slightly to the right — at an angle of approximately 10 to 15 degrees to the Volvo's direction of travel.
In plain terms — the Volvo struck something that was almost directly in front of it and slightly to its right.
IMPACT GEOMETRY — COMBINED ANALYSIS
The damage patterns on both vehicles are consistent with one specific collision geometry:
The Volvo travelling northbound struck the Civic travelling westbound on the Civic's right front quarter — at close to a perpendicular angle.
This is a classic T-bone configuration — one vehicle travelling in one direction strikes the side of another vehicle travelling at approximately 90 degrees to it.
The striking vehicle — the Volvo — shows frontal damage. The struck vehicle — the Civic — shows side damage at approximately 90 degrees to its direction of travel.
This geometry is consistent with James Okafor's account — that he was travelling westbound and was struck on his right side by a vehicle approaching from his right — from the south.
This geometry is inconsistent with Caroline Mercer's account — that James Okafor crossed into her path and struck her.
If James Okafor had crossed into Caroline Mercer's path and struck her — the Civic would show frontal damage and the Volvo would show side damage. The damage pattern is the reverse of what that account requires.
YOUR TASK
The crush analysis has identified a T-bone collision geometry — the Volvo struck the Civic on its right side at close to a perpendicular angle.
Consider what this tells you about which vehicle was the striking vehicle and which was the struck vehicle — and how that relates to the two drivers' accounts.
Research what a T-bone collision is and what the typical damage patterns look like on each vehicle. Consider whether the damage pattern is consistent with Caroline Mercer's account — that James Okafor crossed into her path — or with James Okafor's account — that he was struck on his right side by a vehicle approaching from the north.
The crush analysis has told you the geometry of the impact. Evidence File 04 will use that geometry — combined with the momentum data from Evidence File 02 — to explain exactly how James Okafor's Civic ended up on the northern verge.
EVIDENCE FILE 04 +
EVIDENCE FILE 04 — CAMERA FOOTAGE AND DEBRIS ANALYSIS
Case Reference: MRTI-2024-0914
Evidence Item: EV-04 — Traffic camera footage review and debris field mapping
Prepared By: DC Priya Nair, Road Traffic Investigation Unit
Date: Friday — 3:30 PM
BACKGROUND
Two additional evidence sources remained unexamined — the traffic camera footage from the lamp post at the northwestern corner of the intersection, and the distribution of debris across the road surface. Both provide independent corroboration of the collision geometry established in Evidence File 03.
PART ONE — CAMERA FOOTAGE
The camera mounted on the lamp post at the northwestern corner of the intersection recorded continuously on the night of the collision. Heavy rain obscured the lens at the moment of impact — the critical frame is not recoverable.
However the ten seconds of footage immediately before impact are intact and analysable.
Footage analysis — James Okafor — Silver Honda Civic:
The Civic is first visible at the eastern edge of the camera frame at T-9 seconds — travelling westbound on Harwick Lane.
At T-3 seconds the Civic's brake lights illuminate — consistent with the EDR recording brake application beginning at T-3 seconds before collision. The Civic is visibly decelerating.
At T-2 seconds the Civic enters the intersection from the east. Its trajectory is consistent with westbound travel on Harwick Lane — no deviation toward the northbound lane of Millfield Road is visible.
Footage analysis — Caroline Mercer — Dark Blue Volvo Estate:
The Volvo is first visible at the southern edge of the camera frame at T-6 seconds — travelling northbound on Millfield Road.
No brake lights are visible on the Volvo until T-2 seconds — consistent with the EDR recording brake application beginning at T-2 seconds before collision.
At T-2 seconds the Volvo is still south of the give-way line — moving at speed.
At T-1 second the Volvo crosses the give-way line. The Civic is already in the intersection.
At T-0 the lens is obscured by rain.
FOOTAGE SUMMARY
The camera footage establishes the following sequence in the final two seconds before impact:
At T-2 seconds — the Civic enters the intersection travelling westbound. The Volvo is still south of the give-way line.
At T-1 second — the Volvo crosses the give-way line. The Civic is inside the intersection.
The Civic entered the intersection before the Volvo crossed the give-way line.
PART TWO — DEBRIS FIELD ANALYSIS
When vehicles collide they shed debris — glass fragments, plastic trim, paint flakes, and fluid deposits — at or near the point of impact. The distribution of this debris identifies the primary point of contact between the two vehicles.
DC Nair mapped the debris field at first light using a grid reference system anchored to the intersection centre point.
Primary debris concentration:
The heaviest concentration of glass fragments, plastic trim, and paint transfer was located at a point 1.4 metres west and 0.6 metres north of the intersection centre — in the westbound lane of Harwick Lane, just inside the intersection.
This is the primary point of impact — where the two vehicles first made contact.
Fluid deposits:
Engine coolant and brake fluid deposits were identified at two locations:
Primary deposit — at the primary impact point — consistent with initial contact rupturing fluid lines on the Civic's right front quarter.
Secondary deposit — 3.2 metres northwest of the primary impact point — consistent with the Civic's final resting position on the northern verge.
No fluid deposits were identified on the northbound lane of Millfield Road south of the intersection — ruling out any collision event in that area.
DEBRIS FIELD INTERPRETATION
The primary debris concentration at 1.4 metres west of centre in the westbound lane tells investigators where the collision occurred — not where the vehicles came from or where they ended up.
The collision happened in the westbound lane of Harwick Lane — James Okafor's lane.
A vehicle travelling westbound on Harwick Lane would be in exactly this position at the moment of impact.
A vehicle travelling northbound that had crossed into the westbound lane would also be in this position — but the camera footage places the Volvo south of the give-way line at T-2 seconds, when the Civic was already at this location inside the intersection.
YOUR TASK
The camera footage and debris analysis have added two independent pieces of evidence to the picture established in Evidence Files 01 through 03.
The camera shows the Civic entering the intersection before the Volvo crossed the give-way line. The debris field places the primary impact point in the westbound lane — James Okafor's lane — not in the northbound lane where Caroline Mercer's account would require it.
Consider what the camera footage establishes about who entered the intersection first — and what the debris field establishes about where the collision occurred. Do both pieces of evidence support the same conclusion — and is that conclusion consistent with the crush analysis in Evidence File 03?
Research how debris field analysis is used in collision reconstruction. Consider what the location of the primary debris concentration tells you about where the two vehicles were at the moment of impact — and whether that is consistent with either driver's account.
Evidence File 05 will use the momentum data from Evidence File 02 and the impact geometry from Evidence File 03 to reconstruct exactly what happened after the collision — and explain definitively how James Okafor's Civic ended up on the northern verge.
EVIDENCE FILE 05 +
EVIDENCE FILE 05 — MOMENTUM RECONSTRUCTION AND FINAL ANALYSIS
Case Reference: MRTI-2024-0914
Evidence Item: EV-05 — Vector momentum analysis and collision reconstruction
Prepared By: Dr. Peter Osei, Collision Reconstruction Specialist
Date: Saturday — 9:00 AM
BACKGROUND
Four evidence files have established the approach speeds, directions, impact geometry, camera sequence, and debris field for this collision. This file uses the physics of momentum and vectors to reconstruct what happened after the two vehicles made contact — and to explain definitively why James Okafor's Civic came to rest on the northern verge despite travelling westbound.
MOMENTUM — KEY CONCEPT
Momentum is the product of an object's mass and its velocity:
Momentum = Mass × Velocity
Momentum is a vector quantity — it has both magnitude and direction. When two objects collide their combined momentum is conserved — the total momentum after the collision equals the total momentum before it. This is the Law of Conservation of Momentum — one of the most fundamental principles in physics.
In a vehicle collision this means the combined momentum of both vehicles at the moment of impact determines the direction and speed at which they move immediately after contact.
A heavier vehicle travelling at higher speed carries more momentum — and in a collision it will push a lighter, slower vehicle in the direction it was travelling.
MOMENTUM CALCULATIONS — AT POINT OF IMPACT
Converting speeds to metres per second for calculation:
James Okafor — Civic:
Mass: 1,200 kg
Speed at impact: 19 mph = 8.5 m/s westbound
Momentum: 1,200 × 8.5 = 10,200 kg·m/s westbound
Caroline Mercer — Volvo:
Mass: 1,800 kg
Speed at impact: 34 mph = 15.2 m/s northbound
Momentum: 1,800 × 15.2 = 27,360 kg·m/s northbound
VECTOR ANALYSIS — POST-IMPACT DIRECTION
The two momentum vectors must be combined to determine the resultant direction of motion immediately after impact.
Breaking into components — using north as positive and east as positive:
Civic momentum components:
North component: 0 (travelling westbound — no northward momentum)
East component: −10,200 kg·m/s (westbound = negative east)
Volvo momentum components:
North component: +27,360 kg·m/s (northbound)
East component: 0 (travelling northbound — no eastward momentum)
Combined momentum:
North: 0 + 27,360 = +27,360 kg·m/s (northward)
East: −10,200 + 0 = −10,200 kg·m/s (westward)
Resultant direction:
arctan(10,200 ÷ 27,360) = arctan(0.373) = 20.4 degrees west of north = bearing 339.6 degrees
The combined momentum of both vehicles at the moment of impact points toward approximately 340 degrees — northwest.
WHAT THIS MEANS FOR THE CIVIC
At the moment of impact the Volvo's northward momentum — 27,360 kg·m/s — was 2.7 times greater than the Civic's westward momentum — 10,200 kg·m/s.
The Volvo struck the Civic on its right front quarter — a T-bone impact at close to 90 degrees. The Volvo's momentum dominated the collision dynamics. The lighter Civic — already moving westward — was pushed by the Volvo's northward momentum into a combined northwest trajectory.
A vehicle that was travelling westbound and is struck on its right side by a heavier, faster vehicle travelling northbound will be deflected northwest — pushed by the striking vehicle's momentum across and beyond the intersection.
Northwest from the impact point — which the debris field placed in the westbound lane of Harwick Lane — is the northern verge of Millfield Road.
Exactly where James Okafor's Civic came to rest.
THE ATTENDING OFFICER'S ERROR
The attending officer concluded that James Okafor's Civic must have been travelling northbound because it came to rest on the northern verge.
The momentum reconstruction shows why that conclusion was wrong.
A westbound vehicle struck on its right side by a heavier northbound vehicle will be deflected northwest by the collision — and will come to rest on the northern side of the intersection regardless of its original direction of travel.
The Civic's final resting position on the northern verge is not evidence that it was travelling northbound.
It is evidence that it was struck by a heavier vehicle travelling northbound.
The two explanations produce identical wreckage positions — but only one is consistent with the crush analysis, the debris field, the camera footage, and the EDR data.
COMPLETE RECONSTRUCTION — FINAL TWO SECONDS
T-2 seconds:
Civic enters the intersection travelling westbound at 22 mph — already decelerating. Volvo is south of the give-way line travelling northbound at 43 mph — brake application just beginning.
T-1 second:
Civic is in the westbound lane — 1.4 metres west of centre. Volvo crosses the give-way line at 38 mph — still decelerating. The Civic has priority. The Volvo is required to give way.
T-0 — impact:
Volvo travelling at 34 mph strikes the Civic travelling at 19 mph on the Civic's right front quarter at close to 90 degrees. Primary debris deposited at impact point — 1.4 metres west of centre in the westbound lane.
Post-impact:
Combined momentum directs both vehicles northwest. The Civic — lighter and struck on its side — is deflected northwest and comes to rest on the northern verge 3.2 metres from the impact point. The Volvo — heavier and already decelerating — comes to rest near the intersection centre having shed most of its northward momentum through the impact.
The reconstruction is consistent with every piece of physical evidence across all five files.
YOUR TASK
You now have all five Evidence Files.
The tyre marks established approach directions and speeds. The EDR data revealed Caroline Mercer was travelling at 48 mph in a 30 mph zone. The crush analysis identified a T-bone geometry — the Volvo struck the Civic's right side. The camera footage showed the Civic entering the intersection before the Volvo crossed the give-way line. And the momentum reconstruction has explained why the Civic ended up on the northern verge.
Using evidence from all five files — who caused the collision at the intersection of Harwick Lane and Millfield Road at 12:17 AM? Build your case using the physics — momentum, vectors, impact geometry, and the EDR data — and explain why the attending officer's initial conclusion was incorrect.
Consider also James Okafor's 0.04 alcohol reading. The EDR shows he was braking progressively and steering correctly. The debris field and camera footage place him in the correct lane at the correct time.
Does the alcohol reading change anything — or is it irrelevant to what the physics tells you happened?
HAVE YOU SOLVED THE CASE?
Review the evidence and decide what you think happened. If you're investigating with others, discuss your findings and agree on your final verdict before revealing the answer.
Once your team has reached a conclusion, reveal the answer.