# Survey of Smart Parking Systems
## 7 Discussion and Open Problems
### Information Gathering  
Every SPS needs accurate information on the status of each parking slot to provide the information to users, establish routes that guide drivers, or predict availability or occupancy in certain time segments. As analyzed and classified in Section 4, VDT for parking slots, which can be obtained from various sources, provide information on the availability of the parking spaces. Table 8 shows that sensors predominate as elements for sensing and obtaining the required data. There are different types of sensors such as ultrasonic, magnetic, or light that fall into the IRS category. On the other hand, video processors, image detection, infrared sensors, or RFID are also classified as ORS. While the sensors are highly accurate in measuring the information they provide [163], to operate, they require an underlying infrastructure [4], for instance, the purchase of and installation in each parking slot, plus nodes or antennas that collect the information, and servers that receive and provide \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **SPS** & **City** & **Strengths** & **Weaknesses** \\ \hline \multirow{4}{*}{[26]} & \multirow{4}{*}{PGIS} & \multirow{4}{*}{
\begin{tabular}{c} Boston, United States \\ of America (USA) \\ \end{tabular} } & & Provides information to users on & \\  & & & availability and guides them to & No information is given about the \\  & & & available locations. & sensors used. \\  & & & Information is updated in real time. & Is implemented in a semi-public and \\  & & & Results indicate a reduction in & closed parking lot. \\  & & & parking space search time. & & \\ \hline \multirow{4}{*}{[204]} & \multirow{4}{*}{SD} & \multirow{4}{*}{Santander, Spain} & Has a web interface for users. & Uses DFTP. \\  & & & Is implemented in public car parking & Just sets up a parking prediction and \\  & & & spaces along the road. & does not indicate available/occupied \\ \hline \multirow{4}{*}{[21]} & \multirow{4}{*}{PRS} & \multirow{4}{*}{Taichung, Taiwan} & Offers alternative booking or free & Is implement in a closed parking slot. \\  & & & access to the parking slot. & Vehicles need an RFID reader to enter \\  & & & Provides a mechanism to avoid & the parking lot. \\  & & & disputes over the parking slot. & \\ \hline \multirow{4}{*}{[223]} & \multirow{4}{*}{SD} & \multirow{4}{*}{Riyadh, Saudi Arabia} & Results show a high level of accuracy & Just implements a detection method. \\  & & & in the sensed data. & Does not provide information to users. \\ \hline \multirow{4}{*}{[217]} & \multirow{4}{*}{SD} & \multirow{4}{*}{Pisa, Italy} & Results show a high level of accuracy & \multirow{4}{*}{Camera and sensor installation} \\  & & & in the sensed data. & are complex. \\ \cline{1-1}  & & & Is implemented in public car parks on & - First version tested does not provide \\ \cline{1-1}  & & & Information is updated in real time. & information to users. \\ \hline \multirow{4}{*}{[179]} & \multirow{4}{*}{CAPS} & \multirow{4}{*}{Zhejiang, China} & Provides information to users on & \multirow{4}{*}{No information provided to guide users} \\  & & & availability of parking. & \\ \cline{1-1}  & & & Information is updated in real time. & \\ \cline{1-1}  & & & Offers the possibility of paying for & concerning available locations. \\ \cline{1-1}  & & & parking through a & \\ \cline{1-1}  & & & third-party application. & \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Implemented works: principal strengths and weaknesses. all the sensed data [101]. This implies a cost that local government or private parking lots must consider when implementing an SPS to facilitate the task of parking for their citizens or users. Even though most of the solutions implement the sensors described, other alternatives may allow intelligent parking systems to be implemented at a lower cost. For example, the crowdsourcing systems offer the possibility of sensing the parking activity of a large number of drivers using data collected from their smartphones via an app [143].