How to show vehicle direction of travel in an accident diagram

One arrow per vehicle, attached to the vehicle

Draw each vehicle's travel arrow starting at or just behind the vehicle, pointing along its actual path. An arrow floating in a lane is ambiguous — attached to V1, it is V1's testimony.

The vehicle's own orientation must agree with its arrow. A car pointing north with an arrow pointing west reads as an error and undermines the whole diagram.

Show the path, not just the heading

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 arrow tool in segments, or use the pen for a freehand curve — then place the vehicle at the point of impact along that path.

Intended maneuver vs. actual movement

"V1 was turning left" (intent) and "V1 traveled straight through the intersection" (movement) can both be true in sequence. When intent matters, note it in the narrative and reserve the arrows for what physically happened. Never draw an arrow for a movement that did not occur.

Direction needs a compass

"Northbound" only means something if the diagram shows north. Drag the compass in the editor so it matches the real orientation of the scene, and the words in your narrative and the arrows in your diagram will finally agree.