Pavements engineering for urban applications is unique and differs in many aspects to that of rural or highway applications. This represents a challenge for major municipal agencies in maintaining the desired level of serviceability of pavements in the most cost effective manner. Over the past decade, the City of Calgary has initiated a number of processes and technologies to address the unique demands of urban pavements.
Transit bus traffic, not typically encountered in rural applications, represents the most significant loading to which an urban major roadway is subjected in many cases. The loading associated with articulating transit buses can be ten times or more than that of a standard single unit truck. In addition, the stresses of this type of loading can significantly impact surfacing materials and the resulting performance, and the potential move to electric transit bus types will further increase the effects of these vehicle types. Instability rutting of flexible pavements, and in particular intersection rutting is another aspect of pavement performance that is relatively unique to the urban context. This represents not only a pavement distress causing a reduction in service life, but a significant safety concern. The use of reclaimed materials is generally more of a consideration in the urban context, due to the significant ongoing supply of materials such as Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS). Although, jurisdictions such as the City of Calgary have been leaders in utilizing these types of materials, there needs to be a compromise between increased use of reclaimed materials and pavement performance. Other aspects of urban pavements represent restrictions that must be accommodated in the design and construction processes. Underground utilities and the need to maintain pavement surface elevations result in impacts on potential subsurface activity, while decreasing the number of options available to rehabilitate and maintain roadways. Traffic accommodation and maintaining business access are also challenges that must be considered during the design and construction of urban pavement rehabilitation and reconstruction.
The City of Calgary has, over the past number of years, developed processes and considered newer technologies in addressing the unique challenges of urban pavement performance. This paper will discuss many of these initiatives including enhanced specification development, use of newer technologies to minimize intrusive testing and the implementation of alternate materials for roadway construction (such as Stone Matrix Asphalt (SMA) Polymer Modified Asphalt Binders (PMA) and concrete pads at bus stops). The paper will also discuss the City’s experience with the use of RAP and RAS, and some of the limitations that have been experienced.
Johnston, A.
Lakkavalli, V.
Sharma, V.
