Choosing intervals for a traffic count

Set the counting rule

Shorter bins show sharper peaks but require more frequent attention. The right interval depends on the question and the observer's workload.

Put the rule into practice

Steps for a reliable tally

1. Set the interval length before starting and use a clock to change bins at exact boundaries.
2. Preserve the raw interval counts when summing a total.
3. Add the interval totals and compare with the full-session count.
4. If they differ, review the boundary times and any traffic observed at the switch.

Why this detail matters

A total alone can hide the time of highest demand. Equal intervals preserve that pattern, while a single running counter can lose the boundaries. Save each interval before resetting or use a new named counter for the next bin. Keep the timezone and date with the final file.

In the field

Save each bin's value at the boundary rather than trying to reconstruct it from a final total. If the observer misses a boundary, note the actual start and end time of that bin. Equal-length intervals are easiest to compare, but an honest irregular interval is better than a falsely labeled regular one.

What can go wrong?

Unequal bins should not be compared as though they represent the same duration.

Common questions