A Concept of Surface Roughness Index for Cycle Path: Bicycle Ride Index (BRI)

On cycle paths, surface roughness is one of the dominant measures related to the level of service for cyclists. Then, in recent years, the demand for the maintenance and improvement of cycle path surfaces increases in terms of ride quality all over the world. However, the conventional approaches to the roughness evaluation are based on the viewpoints of four-wheel motor cars especially in terms of the International Roughness Index (IRI). The purpose of this study is to introduce a concept of a profile-based index which is the Bicycle Ride Index (BRI) suitable for cycle paths considering bicycle vibration responses to the surface roughness. BRI is based on a two degree of freedom model which is compatible with the quarter-car model for the IRI. To reproduce the interaction between road surface and bicycle, this study employs four types of bicycles such as hybrid bike, electric hybrid bike, electric city bikes for considering parameters of the model by performing vibration tests. As a result, the bicycles have two resonance frequencies around 10 and 20 Hz in the body and axle masses assuming handlebar and front wheel, respectively. This result proves that bicycles respond to wavelengths ranging from 0.1 to 1.0 m at normal traveling speed as 15 km/h unlike the conventional definition of “roughness” that covers wavelengths ranging from 0.5 to 50 m. This study also describes the definition of BRI which is applied to the same data accumulation procedure as the IRI.