Investigation of the clear sight areas on suburban roundabouts

Ahac, Saša; Kipa, Petra · 2022 · Crossref

DOI: 10.5592/co/cetra.2022.1348

archive: archived pipeline: cataloged verified

Get this paper ↗ (DOI — opens at the source; we link to it, we don't host it)

Summary

This paper investigates the evaluation of clear sight areas on suburban single-lane roundabouts, addressing the critical safety requirement that drivers without the right of way must have adequate visibility to enter traffic safely. Motivated by the global proliferation of roundabouts and the lack of standardized procedures for sight distance evaluation, the study compares design standards from Australia, Croatia, and Italy. These countries were selected due to their significant roundabout infrastructure and diverse regulatory approaches. The research aims to identify key influential parameters, highlight discrepancies in existing guidelines, and specifically critique the limitations of Croatian regulations. The methodology involves a critical review of the aforementioned national standards, focusing on how they define intersection sight distance and circulating carriageway sight distance. The authors categorize existing approaches into three distinct methods for intersection sight distance and two for circulating carriageway visibility. To empirically compare these standards, the researchers applied the guidelines to a theoretical four-legged, single-lane suburban roundabout with a 20-meter outer radius. The analysis assumed an approach speed of 50 km/h and a circulating speed of 25 km/h. Australian guidelines were adapted for right-hand traffic to ensure comparability. The study calculated the resulting clear sight areas based on specific parameters such as driver eye height, obstacle height, and required path lengths defined by each standard. The results demonstrate significant variation in the size and construction of clear sight areas depending on the regulatory framework. The Australian guidelines produced the largest total clear sight area, driven by a mandatory minimum sight distance of 70 meters to the left, based on a five-second critical acceptance gap. Conversely, the Italian standard yielded the smallest clear sight area, relying solely on geometric tangents relative to the roundabout’s outer radius and central island, without specifying driver eye or obstacle heights. The Croatian guidelines produced intermediate results but revealed a critical design flaw: the required clear sight area extends over the entire central island, failing to obstruct the line of sight toward the opposing exit. This lack of obstruction contradicts the principle that visibility across the central island should be limited to prevent entering drivers from neglecting the right of way of circulating vehicles. The study concludes that sight distance evaluation approaches vary widely in complexity and parameter dependency. While Australian and Croatian guidelines provide detailed instructions based on vehicle speed and stopping distances, the Italian standard offers only basic geometric instructions. The authors identify a specific deficiency in Croatian guidelines, noting that they do not adequately mandate the obstruction of sight lines across the central island, which could compromise traffic clarity and safety. The paper recommends improving Croatian guidelines by incorporating requirements for vegetation or traffic equipment to limit sight distance over the central island. Future research is proposed to include regulations from Spain, Portugal, Slovenia, and Poland to further refine recommendations for roundabout design standards.

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed.

Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• intersection design