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 fastest and most accurate.

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 vehicle a travel arrow, 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.

Finish with a short written narrative. A picture plus three sentences beats either one alone.

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. Remember the diagram is illustrative: verify measurements independently before official use.

The whole method on one example

Here is the five-step order applied to a typical case, with illustrative values. A sedan (V1) northbound on a two-lane road begins a left turn into a driveway; a motorcycle (V2) is overtaking it at that moment. They collide at the entrance of the driveway.

Step 1: the road first. The two-lane template, plus a short custom road for the driveway, drawn with the road tool and snapped to the main road's edge. Step 2: V1 drawn angled mid-turn across the oncoming lane, V2 in the oncoming lane where it struck. Step 3: a curved arrow for V1's turn, a straight arrow for V2's overtake, X1 at the driveway mouth; the only context element added is the van parked before the driveway that mattered for what V2 could see. Step 4: plates on both vehicles; two measurements — X1 to the driveway's north edge (approx. 2 m) and the parked van's rear to the driveway (approx. 6 m); north set to match the road's real bearing. Step 5: a three-sentence narrative and export.

Total drawing time with a tool that handles the geometry for you: about five minutes. The order is what made it fast: every element landed on something already in place, so nothing had to be redrawn.

Before you leave the scene

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 measurements from the list above, 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.