## 4 Limitations of Past Research and Implementation Barriers
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Researchers** & **Methodology** & **Findings** & **Limitations (for Future Works)** \\ \hline \hline \multirow{4}{*}{[PERSON] et al. [1]} & & - & AV and ride-sharing interaction & - & Prioritisation SAVs. \\  & Analytical & & needed for AV-PRTs. & - & Policy and regulations. \\  & & - & AV-buses need dedicated roads. & - & Lane-keeping and docking. \\  & & - & Vehicle fatality rates may reduce. & - & Mode-choices effects. \\  & & - & Vehicle gap reduction. & - & Ride-sharing \\ \multirow{4}{*}{[PERSON] and [PERSON] [11]} & \multirow{4}{*}{Analytical} & - & High penetration rate is needed & - & Increase in traffic due to AV use as a private vehicle. \\  & & - & Data privacy, hacking, security, & - & - \\  & & - & cost and regulatory concerns exist. & - \\ \multirow{4}{*}{[PERSON] and [PERSON] [13]} & \multirow{4}{*}{Analytical} & - & Ride-sharing will increase. & - & Mode shift effects. \\  & & - & Lower GHG and energy use. & - & Electric power grid source. \\  & & - & Traffic congestion will decrease. & - & Growth in car traffic. \\  & & - & VMT will change. & - & Occupancy level. \\  & & - & VMT will change. & - & Mixed-use traffic. \\  & & & - & Dynamic ride-share (DRS). \\  & & - & Ride-sharing had positive results. & - & Life-cycle impacts. \\  & & - & Single SAV can replace 11 CVs. & - & Simulation of actual data. \\  & & - & SAV adds 10\% in travel distance. & - & Different types of vehicles. \\  & & - & Most travelless waited for \(\leq 5\) min. & - & Real traffic speed changes. \\  & & - & SAV sedans decreased energy & - & SAV relocation for parking. \\ \multirow{4}{*}{[PERSON] and [PERSON] [14]} & \multirow{4}{*}{Agent-based model} & \multirow{4}{*}{Agent-based model} & \multirow{4}{*}{light-duty vehicles.} & \multirow{4}{*}{-} & Modelling of longer trips. \\  & & - & GHC emissions decreased by & - & SAV occupancy levels. \\  & & 5.6\%. & - & SAV replacement rate. \\  & & - & SO\({}_{2}\), PM and NO\({}_{x}\) reduced by & - & Alternate SAV fuel. \\  & & 19\%, 6.5\% and 18\%, respectively, & - & Emission regulations. \\  & & - & Mode to CAVs. & - & Mode choice, destination and \\  & & - & SAVs used \(<\) 10\% of CV parking & - & AV technology aspects. \\  & & - & SAVs provide high service level. & - & Socio-economics. \\  & & - & SAVs increased travel time by \(\leq\) & - & Transport system analysis. \\ \multirow{2}{*}{[PERSON] [22]} & \multirow{2}{*}{Simulation modelling} & \multirow{2}{*}{-} & \multirow{2}{*}{Benefits of SAVs are dependent on user’s willingness to accept ride-sharing.} & \multirow{2}{*}{-} & \multirow{2}{*}{Sharely and legal aspects.} \\  & & - & DRS of SAVs reduces travel cost. & - & \\  & & - & Private operators can earn 19\% & \\ \multirow{2}{*}{[PERSON] and [PERSON] [24]} & \multirow{2}{*}{Simulation modelling} & \multirow{2}{*}{-} & \multirow{2}{*}{DRS critical in limiting VMTs.} & \multirow{2}{*}{-} & Traffic emissions. \\  & & - & DRS reduce waiting by 4.5 min. & \\  & & - & Service time reduced by 0.3 min. & \\ \multirow{6}{*}{[PERSON] et al. [26]} & \multirow{6}{*}{Microscopic simulation} & \multirow{6}{*}{-} & \multirow{6}{*}{ACC had minimal change on lane capacity.} & \multirow{6}{*}{-} & Dynamic response of ACC systems. \\  & & - & Cooperative ACC can increase lane capacity (almost double) with high market penetration rate & - & Response to a strong traffic disturbance. \\  & & & (around 100\%). & - & Emergency stopping conditions. \\  & & - & Restricted AV-bus use showed & - & Restricted trials. \\  & & - & user acceptance. & - & Regulations. \\ \multirow{4}{*}{[PERSON] and [PERSON] [28]} & \multirow{4}{*}{Analytical} & \multirow{4}{*}{-} & AV-buses have less likelihood of speed-limit violations.} & \multirow{4}{*}{-} & Mode-shift and mode choices \\  & & - & AV-bus showed reduced fuel & - & Sustainable development. \\ \multirow{4}{*}{[PERSON] and [PERSON] [28]} & \multirow{4}{*}{Analytical} & \multirow{4}{*}{-} & \multirow{4}{*}{AV-bus showed reduced fuel} & \multirow{4}{*}{-} & Infrastructure design. \\  & & - & consumption and emissions. & - & System-wide integration. \\ \hline \hline \end{tabular}
\end{table}