Roundabout Count Methodology

Definition and purpose

A roundabout count follows movements from an entry arm to a selected exit arm, with the site layout and movement labels established before observation begins.

Use it to understand how traffic distributes through a roundabout for access, operational or design studies.

Required inputs

• Roundabout layout and arm labels
• Entry-to-exit movement matrix
• Periods, intervals and classes
• Active-travel scope
• Output template

Video and camera considerations

Footage should show each included entry and exit clearly enough to distinguish an entry-to-exit path. Large or multi-lane roundabouts may need more than one source viewpoint.

Observation, classification and intervals

Observation process

Record each agreed entry, exit and relevant circulating path against the movement matrix. Keep arm naming consistent between site plan, workbook and final files.

Movement and classification process

Classify at the point specified by the brief, using a documented class scheme. Active-travel observations are kept separate where requested.

Time intervals

Use the approved interval structure consistently across all arms; do not combine partial intervals without a note.

Validation and QA/QC

Check that entry totals reconcile with mapped exit movements for the observed scope and investigate missing paths or atypical entries.

Common problems and limitations

• A central island or vegetation can hide exit choices.
• Multi-lane entries can make a late path change hard to see.
• Inconsistent arm labels can invalidate a matrix.

It is an observed movement record, not a simulation or a prediction of future operation.

Typical deliverables

• Entry-exit movement tables
• Classified or active-travel splits where scoped
• Layout/matrix reference
• Quality and exception notes

Illustrative output format

Illustrative sample data only — not a project result or benchmark.

Frequently asked questions