Development of Recommended Guidelines for Preservation Treatments for Bicycle Routes
This project was a continuation of a previous study that focused on the effects of pavement macrotexture on bicycle ride quality using input from bicycle club members and their bicycles on state highways, and considered changes to Caltrans chip seal specifications that resulted in seals with larger maximum size stones being typically used. This second project included a wider range of bicycle riders and bicycle types, considered pavement roughness and distresses in addition to macrotexture, and included measurements on urban preservation treatments and city streets as well as on treatments on state highways and county roads. This study also examined preservation treatment aggregate gradations and the mechanistic responses of bicycles to pavement macrotexture and roughness. The results of both projects were used to prepare recommended guidelines for the selection of preservation treatments that are best suited to bicycle routes on California’s state highways and local streets. Macrotexture, roughness, and pavement distresses were measured for different preservation treatments on 67 road sections distributed in five northern California and Nevada cities (Davis, Richmond, Sacramento, Reno, and Chico) and on a number of Caltrans highway sections and county roads. Bicycle ride quality surveys were conducted with a total of 155 participants. Correlations of pavement texture, bicycle vibration, and bicycle ride quality were developed. Correlations between pavement roughness and distresses, correlations between bicycle ride quality and roughness, and correlations between pavement texture and treatment specifications were preliminarily explored. Models for bicycle ride quality and physical rolling resistance were also developed. Long-term monitoring of pavement macrotexture for larger stone seals on LA-2, SLO-1, and Mon-198 was completed to determine how much texture is reduced by traffic. Major conclusions drawn from the results and analyses include the following: 1) changes in Caltrans chip seal gradation specifications have resulted in higher macrotexture values, as seen on example sections on LA-2, SLO-1, and Mon-198; 2) preliminary (first study on highways plus second study on streets) results show that 80 percent of riders rate pavements with mean profile depth (MPD) values of 1.8 mm or less as acceptable and 50 percent rate pavements with MPD values of 2.3 mm or less as acceptable; 3) most slurry seals on city streets produce high acceptability across all cities; 4) a clear relationship was found between the critical aggregates sizes (#4 and #8 [4.26 and 1.18 mm]) and MPD; 5) pavement texture generally tends to decrease over time due to traffic; 6) both IRI and MPD are important parameters for determining whether riders find a particular pavement section acceptable; 7) there is considerable variability among people and among sections that influences what bicyclists’ perceive as acceptable pavement condition; and 8) the presence of distresses, particularly cracking, lowers the ratings that riders give to pavements.