# Feasibility Study for Using Piezoelectric-Based Weigh-In-Motion (WIM) System on Public Roadway
## 1 Introduction  
### General Introduction  
The over-loaded trucks have been a critical issue in many countries, which causes more damage to the pavement and reduces the service life of the roadway. Compared with the static weighing system, weigh-in-motion (WIM) system provides the traffic loading data with less accuracy, but much less impact on the traffic flow [1]. The WIM systems weigh vehicles at highway speeds and introduce much less delay to the transportation network than the static one. For these reasons, WIM systems have been widely deployed to support transportation infrastructure management [2; 3; 4]. It also serves as primary weight compliance checkpoints of commercial trucks for weight enforcement [5; 6].  
The total number of trucks in the United States has increased from 60 million to 85 million from 1992 to 2002 [7]. The annual travel mileage of heavy trucks has increased from 99.5 million to 138.6 million miles during the same period [8]. The increased workload promoted the deployment of additional WIM systems and weighing equipment. Installing a permanent WIM system in the pavement can be costly (about $250,000 for a four-lane road [9]. It brings a dilemma to government agencies that either increasing the budget to install more WIM systems by cutting off other projects ortolerating the results of lacking weighing enforcement for today's increasing traffic. Highway Statistic 2017 indicates that the annual miles traveled by vehicles on rural roads decrease slightly from 2007 to 2017 (1,032,790 million miles to 963,206 million miles) [10]. However, according to the chapter \"Growth in Volume and Loadings on the Rural Interstate System\" included in the report Highway Statistic 2013 by Federal Highway Administration, the average daily load on rural roads is increasing annually since 1970 [11]. The average daily load on rural roads in 2013 is almost 6 times greater than in 1970. It indicates that there is a greater chance of overweight violation on rural roads today, which significantly reduces their service life. Researchers are developing new approaches to find alternative methods of weighing vehicles. However, in recent years, most of the development of WIM is conducted for monitoring the traffic over bridges. [PERSON] et al. have developed a weigh-in-motion method to identify the vehicle speed and axle loading on bridges using long-gauge fibre Bragg grating (LGFBG) sensor [12]. [PERSON] et al. proposed an equivalent shear force method to identify vehicle information, including speed and axle loading [13]. The research activities on WIM in the pavement were mostly focused on optimizing the existing system to achieve better accuracy or better understanding of the pavement-WIM interaction. [PERSON] et al. provided an optimization framework for the in-pavement WIM system in their study [14]. [PERSON] and [PERSON] have conducted a comprehensive study to find the weighing accuracy of in-pavement WIM over the pavement/sensor complex behavior [15].  
This paper presented a proof-of-concept evaluation of an alternative to permanent WIM system with much lower cost using the piezoelectric material, which is named as P-WIM. The P-WIM consists of several piezoelectric disks sealed in a protective package made from engineering plastic. The fabricated prototype P-WIMs are installed at the entrance of Troutville Weigh Station near Roanoke, VA. On-site evaluations are performed to find if the installed P-WIMs are capable of capturing the axle loading of passing vehicles. The axle loading data, measured by the Virginia Department of Motor Vehicle (VDMV) using their static weight, was used to find the relationship between the voltage generated from P-WIMs and the actual traffic loading.