One challenge facing transportation agencies employing Spring Weight Restrictions (SWR) is the ability to broadly monitor the road network for critical real time changes in road strength. Some agencies employ a subjective assessment of road roughness changes as a proxy to changes in strength and the need for further weight restrictions, though the geographic scope is limited to the travel of the road supervisor. Smartphone devices have been shown to be effective and accurate mobile platforms for collecting accelerometer data that can be converted into International Roughness Index (IRI) values. These devices have the potential to expand the extent and frequency of roughness monitoring over spring thaw if instrumented on fleet vehicles or crowd-sourced. This could support the development of objective trigger values for changes in roughness that would support the decision-making by a district engineer regarding imposing additional weight restrictions or focusing strength testing. If changes in roughness could be correlated with changes in strength, it may be possible to isolate specific areas of road weakness at high speed and in real-time.
This research explored the potential of using smartphones to monitor road roughness changes on 1 km sections of two proximate collector and local highways over the SWR period in New Brunswick from March 15 – May 17, 2015. IRI values were calculated from an average taken from four runs on 26 different days at a speed of 80 km/h, reduced to 60 km/h on the local highway due to excessive road heaving. IRI values doubled from baseline to peak on both sections (collector and local baseline (peak): 1.35 m/km (2.54 m/km); 3.34 m/km,(6.60 m/km)) within the first two weeks of SWR, returning to baseline values two weeks before SWR ended. Data collection twice a week would capture the majority of significant changes in IRI values between observations. The change from a baseline IRI to the peak IRI and back occurred within the SWR window, suggesting the dates were appropriate if roughness was correlated with strength. Further work should explore trigger values that initiate a protocol to respond to drastic weather changes and the relationship between road strength and IRI.
Allaire, F.
Hanson, T.
