Improving Transferability of Safety Performance Functions by Bayesian Model Averaging
Bibliographic record
Abstract
A jurisdiction can import a safety performance function from another jurisdiction or another time period through model calibration. For the transfer to be achieved successfully, the calibrated model must sufficiently capture local road and traffic features. As proposed in the AASHTO Highway Safety Manual, the model calibration factor is estimated to be the ratio of the sum of observations in a local sample to the sum of predictions for the sample from the uncalibrated model. Although this approach may be adequate for overall goodness-of-fit measures, achievement of a satisfactory fit over all ranges of the covariates is not guaranteed. This paper seeks to address this limitation by investigating a new methodology for the transfer of models with four groups of sample data from Canada and Italy. First, the calibration factor approach was evaluated by the use of goodness-of-fit tests. Then, local models were developed and evaluated. For these models, a variety of random structures for frequentist and Bayesian approaches was explored with generalized linear regression, nonlinear mixed fitting, or Markov chain Monte Carlo simulation procedures. Finally, a Bayesian model averaging approach that integrated all considered models was investigated as an alternative to traditional model selection. This methodology did improve model transferability over all ranges of covariates, suggesting that Bayesian model averaging can be a sound alternative to conventional model calibration, especially when the flexibility and estimation ease of this technique are considered. Moreover, this approach is conceptually superior to selection of a single best model because it explicitly addresses model uncertainty.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.032 | 0.080 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.003 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.004 |
| Open science | 0.003 | 0.004 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".