How to draw a traffic accident diagram, step by step

1. Start with the road, not the vehicles

A common beginner mistake is placing the cars first and squeezing a road around them. Do the opposite: lay down the road geometry first (the intersection, curve or parking aisle), because everything else takes its meaning from the roadway.

In My Traffic Sketch you can pick from 23 road templates, draw your own roads with the road tool, or paste an aerial photo of the actual location and trace over it. If the real location is unusual, the photo route is usually the quickest way to match its real shape.

2. Place the vehicles at the moment of impact

Position each vehicle where it was when the collision happened, not where it ended up. If the rest positions also matter (they often do), draw them as a second set of outlines or note them in the narrative.

Rotate each vehicle to its true angle. A car turning left mid-intersection at 45 degrees tells a completely different story than one drawn square in its lane.

3. Add directions, the impact point and context

Give every moving vehicle a travel arrow (a vehicle that was stopped gets none), mark the point of impact explicitly, and add only the context that played a role: the stop sign one driver missed, the parked truck that blocked the view, the crosswalk. Leave out decoration. Every extra element costs the reader attention.

4. Identify, measure, annotate

Label vehicles V1 and V2 and record the license plates. A diagram where nobody can tell which car is which is a drawing, not documentation. Add the measurements that matter: skid length, distance from a reference point, lane width. Mark north so the reader can orient the scene.

Give each vehicle a short physical description: make, color and damaged area. "Blue Toyota Corolla, front-left fender damage" beats "passenger vehicle". In My Traffic Sketch the plates and descriptions print as a table under the diagram.

Finish with a short written narrative. A picture plus three sentences beats either one alone. The narrative carries what a drawing cannot: the sequence, weather and light, and what each driver said they intended.

5. Export and keep a copy

Export the diagram as a PDF. My Traffic Sketch adds a header with the case data, a table of vehicles with plates and descriptions, your narrative and a legend, so the single page reads as a complete report. The diagram is illustrative, so verify measurements independently before official use.

Arrows and direction of travel

Draw each moving vehicle's travel arrow behind it, along its actual path, with the arrowhead ending at or just behind the vehicle. An arrow floating in a lane is ambiguous. The vehicle's own orientation must agree with its arrow. Backing is the one exception to both rules (see below). A car pointing north with an arrow pointing west reads as an error.

For turns and lane changes, a curved arrow tracing the actual path says far more than a straight one. In My Traffic Sketch, draw the path with the Pen (freehand) or with Line strokes, then finish it with one short Arrow stroke, so only the last piece carries an arrowhead. Four patterns cover most collisions:

• ▸Straight travel: one straight arrow behind the vehicle, along the lane.
• ▸A turn: one curved arrow following the turning path from the approach lane into the exit lane, not two disconnected straight arrows.
• ▸A lane change: an arrow that starts in the original lane well before the impact and curves gently toward the new lane, so the drift is visible. If the vehicle finished the move before the impact, the arrow becomes a shallow S that straightens out in the new lane.
• ▸Backing: a short arrow starting at the vehicle's rear and pointing the way the rear faces, the opposite way to its front, so the reader sees it was reversing. If the rear is up against the other vehicle, draw the arrow alongside the vehicle instead. Slow movement is still movement.

What the arrows should and should not show

Arrows show what physically happened before the impact. When intent matters ("V1 was about to turn left"), put it in the narrative, and never draw an arrow for a movement that did not occur. If vehicles moved between impact and rest, that movement belongs in the narrative or in a clearly marked second outline, not in the same set of arrows.

Give each moving vehicle its own arrow, even when two were going the same way, do not start an arrow at the impact point, and leave out arrows for traffic that was not involved.

"Northbound" only means something if the diagram shows north. Turn the compass to match the real orientation of the scene early. Rotating north after everything is drawn invites exactly the inconsistency you were trying to avoid.

Situations that need one more element

The steps above cover a two-car collision. A few common situations each add one thing the reader will look for:

• ▸Three or more vehicles: number them in the order of the collision sequence, starting with the vehicle that struck first, not the order you noticed them, and add one impact point per contact (X1, X2…). Say the sequence in the narrative.
• ▸Pedestrian or cyclist: their position and direction at the moment of contact, plus the crosswalk or bike lane if there is one. The editor labels a pedestrian P1, P2…; a bicycle is placed like a vehicle, with its own V number. Never label a person by name.
• ▸Parking lot: the aisle direction arrows and stall lines nearest the collision, and which vehicle was backing out. Lots have no lanes in the usual sense, so the aisle arrows do the job lane markings do on a road.
• ▸Lane change or merge: the lane lines on both sides of the change, and where the lane change began, not just where the vehicles touched.
• ▸Hit while parked: the parked vehicle's exact position in its stall or at the curb, and the direction the other vehicle came from, even if it left.

What to leave out

Everything that did not influence the collision: buildings that played no role, every parked car on the block, decorative trees. Ask one question of every element: did it affect what happened, or does it help locate what happened? If neither, delete it.

The same discipline applies to precision. Record each number at the precision of the method that produced it: a tape measure earns one decimal, a measuring wheel whole units, and paces earn "approx." and nothing finer. Do not invent angles to the degree or distances to the centimeter that nobody measured.

Check it before you export

Run the finished diagram through this pass:

• ▸Cover the narrative and ask someone who was not there: can they tell which way each vehicle was going, and point to where they collided?
• ▸Does the sheet say whether the positions shown are at impact or at rest?
• ▸Can each vehicle be told apart by plate or description?
• ▸Can you find north and the scale bar without hunting, and tell which street is which?
• ▸For each number, can you name the tool that measured it?
• ▸Read the narrative while tracing each sentence on the picture. Every claim in the text needs a visible counterpart: an arrow, a position, a mark. If a sentence has nothing to point at, either the drawing is missing something or the sentence is.

What the diagram is for, and what it is not

A traffic accident diagram answers four questions at a glance: where each vehicle was, which way it was going, where they met, and what controlled the movement (a stop sign, a signal, lane markings). People draw one for an insurance claim, for their own records while memory is fresh, to explain the scene to an adjuster over the phone, or to attach to a statement.

It is not a ruling on fault, and it does not replace a police report. A diagram records geometry and observation. Who was responsible is decided from statements, evidence and the official report, not from the drawing, and a careful diagram never pretends otherwise.

Paper, phone or computer?

A pen-and-paper sketch at the scene is better than nothing, and some claim forms still have a small box for one. Its weaknesses are predictable: vehicles drawn out of scale, arrows that point two ways, and a drawing that has to be redone from scratch when one position turns out wrong.

An online diagram tool fixes those three problems: vehicles keep their proportions, every element can be moved without redrawing the rest, and the result exports as a clean PDF or PNG you can attach anywhere. If you sketch on paper at the scene, redraw it the same day while the details are fresh, and keep the original paper sketch with your records.

Four mistakes the site operator sees again and again

Asked on October 30, 2026 which documentation mistakes they see repeatedly, the person who runs this site named these four. Each one makes a diagram harder to trust, and each has a simple fix.

• ▸Moving the vehicles before anyone records where they stopped. If the cars can stay where they are safely, take a few photos of where they came to rest before they are moved. If they have to be moved for safety, or because police tell you to, move them, then say in the narrative that the positions in the diagram were reconstructed after the vehicles were moved.
• ▸Not writing down the plates and the other driver's details. Note every plate at the scene and exchange driver, insurance and vehicle details. On the diagram, give each vehicle its plate with the License plate field, so V1 and V2 can never be mixed up.
• ▸A sketch with no north and no direction of travel. Without a north arrow and an arrow behind each moving vehicle, "the car on the left" tells the reader nothing. Turn the compass to match the scene and give every vehicle that was moving its arrow.
• ▸Too few photos, or photos taken from too far away. Take wide shots from at least two corners to show the layout, then close-ups of each vehicle's damage, each plate and any marks on the pavement. Those photos are what let you redraw the scene correctly later.

Before you leave the scene

People come first. Helping anyone who is hurt, making the scene safe and calling emergency services all come before any documentation. Never move an injured person to take a measurement or a photo.

The diagram can be finished later; the facts cannot. Before leaving, make sure you have:

• ▸Photos of the overall scene from at least two corners, plus each vehicle's damage.
• ▸The key measurements, taken from fixed reference points such as a curb corner or a pole, or honest paced estimates labeled as such.
• ▸Plates, and the position of any traffic control (signal, sign, markings).
• ▸A note of conditions: light, weather, pavement state. They go in the narrative.

Frequently asked questions

Do I need to know how to draw? No. A readable diagram depends on order and completeness, not on drawing skill: road first, then vehicles at impact, then arrows, impact point and labels.

Can I make it on my phone? Yes. The editor runs in the phone's browser, with no app to install and no account, and the draft is saved on the device.

Do I include the other driver's personal information? Plates and vehicle descriptions, yes. Names, phone numbers and insurance details usually belong on the claim or exchange form, not on the drawing itself.

What if I do not know exactly where the impact happened? Mark your best estimate and say so in the narrative. An honest "approximate" keeps the rest of the diagram credible.