How to measure an accident scene for your diagram

Anchor everything to fixed reference points

A distance means nothing without a starting point that will still exist next month. Use permanent features: the corner of a curb, a utility pole, the stop line, a hydrant. Measure from those to the vehicles and marks — not from one temporary thing to another.

What to measure, in priority order

If time is short, capture these first:

• ▸Final rest position of each vehicle (two measurements each, from different reference points, roughly at right angles).
• ▸Length and direction of skid or yaw marks.
• ▸The point of impact's distance from a fixed reference.
• ▸Road and lane widths.
• ▸Sight-line distances if visibility was a factor.

Feet or meters — pick one and stay consistent

Mixed units are one of the quietest ways a diagram loses credibility. Decide the unit before the first measurement. My Traffic Sketch works in either — set feet or meters once and every measurement label and the scale bar follow.

Recording measurements on the diagram

Draw each measurement as its own labeled dimension line between the two points it connects — not as a number floating in space. Keep the grid scale honest: if one square is 5 ft, resist stretching a vehicle to "look right" at the cost of the scale.

Be explicit about precision. A paced estimate is fine if it is labeled as one. What damages credibility is presenting estimates as measurements — diagram distances are illustrative until verified with proper equipment.