## 2 Materials and Methods
### Inclusion Criteria  
Our research strictly adheres to the PRISMA guidelines (Figure 1). For literature retrieval, we employed the Topic (TS) field rather than limiting it to Title (TI), which searches the title, abstract, keyword plus, and author keywords, ensuring a comprehensive capture of terminology related to VRUs, wearable technology, and traffic safety appearing  
\begin{table}
\begin{tabular}{l l} \hline
**PICo Element** & **Search Keywords** \\ \hline Population (P) & TS = (“vulnerable road user“ OR pedestrian” OR cyclist” OR bicyclist” OR motorcyclist” OR scooter* OR (“visually impaired” OR blind”) OR (“hearing impaired” OR deaf”) OR (“mobility impair” OR “wheelchair user”)) \\ \hline Phenomenon of Interest (I) & TS = (wearable* OR ((haptic* OR tactile* OR vibrotactile* OR vibration*) NEAR/3 (feedback OR cue* OR alert* OR warming”)) OR ((visual* OR light* OR LED* OR “ambient light”) NEAR/3 (feedback OR cue* OR alert* OR warming”)) OR ((audio* OR auditory* OR sound*) NEAAR/3 (feedback OR cue* OR alert* OR warning”)) OR ((multidonald* OR multisensor* OR multisensory) NEAR/3 (feedback OR cue* OR alert* OR warming”) OR ((smart* OR safe*) NEAR/3 (helmet* OR glasses OR cap* OR vest* OR jacket* OR watch* OR wristband* OR glove* OR shoe* OR insole* OR belt*))) \\ \hline Context (Co) & TS = (“road safety” OR “traffic safety” OR “intersection safety” OR (collision avoid* OR collision warm* OR crash avoid* OR crash prevent* OR “accident prevention”) OR (road hazard* OR traffic hazard*) OR (“street navigation” OR “road navigation” OR “urban navigation” OR “outdoor navigation” OR “traffic navigation” OR “route navigation” OR “bike navigation” OR “bicycle navigation” OR “pedestrian navigation” OR “crosswalk navigation” OR “intersection navigation” OR “intersection navigation” OR “street crossing”) \\ \hline \end{tabular}
\end{table}
Table 1: Search strategy for wearable devices for VRU safety.  
in titles, abstracts, and keywords. We avoided using the ALL field to maintain compatibility with the NEAR/3 proximity operator, thereby optimizing retrieval precision.  
The literature search was completed on 4 May 2025, covering publications from 2000 to 2025. After excluding the non-English literature, review articles, and conference abstracts, we retrieved 462 records. During the title and abstract screening phase, we excluded 386 publications irrelevant to our research focus, allowing 76 publications to proceed to the full-text assessment stage. Based on predefined inclusion and exclusion criteria, we further excluded 18 non-compliant publications during the full-text evaluation. Ultimately, 58 publications that fully met the research requirements were included in our final analysis.  
Papers were included in this review if they met the following criteria:  
* Coverage of all three core elements of the PICo framework: focusing on VRUs, involving wearable technology applications, and targeting traffic safety;
* Written in English.  
Papers were excluded if they had any of the following characteristics:
* Absence of traffic hazard scenarios (e.g., wearable technology only used for indoor applications);
* Literature review article.