Stopping Sight Distance Requirements for Basic Turbo Roundabouts
Bibliographic record
Abstract
Turbo roundabouts, originating from the Netherlands, have been proven to have safety and operations benefits compared to traditional multilane roundabouts. Turbo roundabouts are gradually being adopted by North American transportation and road authorities. However, no design guidelines have been developed yet per North American practices. Sight distance requirements were not even specifically addressed in the Dutch mature design guidelines for turbo roundabouts. This paper focuses on basic turbo roundabouts, examines stopping sight distance (SSD) characteristics, recommends SSD requirements for three critical locations—circulatory roadway, entry approach, and crosswalk on the exit approach—based on AASHTO and Transportation Association of Canada’s (TAC’s) SSD guidelines, presents analytical models, and develops design guidelines for the required lateral clearance and intersection clear sight triangles to meet the required SSD. The values of the required SSD at the circulatory roadway and to the crosswalk on the exit approach equal the values for the speeds. The required approach SSD is the same as for any roadway section with the same design speed. The minimum crosswalk setback of a one-vehicle gap of 6.0 m between the queued vehicle and the crosswalk is sufficient to meet the required SSD. The required lateral clearance and intersection clear sight triangles are recommended. The recommended guidelines would help develop future design guides per North American practices and provide a guide to property needs for planning basic turbo roundabouts.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".