# A Survey of Methods and Technologies for Congestion Estimation Based on Multisource Data Fusion
## 4 Data Collection Technologies
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & & **Definition** & **Equation** \\ \hline Delay & \(d\) & \begin{tabular}{c} The additional travel time experienced by a driver, difference between actual travel time \(TT\) \\ and free-flow travel time \(TT_{0}\) \\ \end{tabular} & \(d=TT-TT_{0}\) \\ \hline Travel Time Index & \(TTI\) & \begin{tabular}{c} The ratio between delay \(d\) and free-flow travel \\ time \(TT_{0}\) \\ \end{tabular} & \(TTI=\frac{d}{TT_{0}}\) \\ \hline Speed Reduction Index & \(SRI\) & \begin{tabular}{c} The ratio between free flow speed \(v_{0}\) and actual \\ speed \(v\) difference over free flow speed \(v_{0}\) \\ \end{tabular} & \(SRI=\frac{v_{0}-v}{v_{0}}\) \\ \hline Buffer Index & \(BI\) & \begin{tabular}{c} The extra time that travelers must add to their \\ average travel time when planning trips to \\ ensure on-time arrival \\ \end{tabular} & \(BI=\frac{d}{TT_{new}}\) \\ \hline Travel Rate Index & \(TRI\) & \begin{tabular}{c} The additional time that is required to make a \\ trip because of congested conditions on \\ the roadway. \\ \end{tabular} & \(TRI=\frac{TT_{par-hour}}{TT_{new-pred}}\) \\ \hline Proportion Stopped Time & \(PST\) & \begin{tabular}{c} The ratio of stopped time \(T_{s}\) to the total journey \\ time \(T_{r}\) (running time) \\ \end{tabular} & \(PST=\frac{T_{s}}{T_{s}+T_{s}}\) \\ \hline Acceleration Noise & \(AN\) & \
\begin{tabular}{c} Induce fluctuation in speed where \(\Delta t_{i}\) is the time \\ interval taken for a speed change \(\Delta v_{i}\) and \(T_{r}\) is \\ vehicle running time \\ \end{tabular} & \(AN=\sqrt{\frac{1}{T_{s}}\sum\limits_{i=1}^{N}\frac{\Delta v_{i}^{2}}{\Delta t _{i}}}\) \\ \hline Acceleration Noise Index & \(ANI\) &
\begin{tabular}{c} The ratio between actual acceleration noise and \\ acceleration noise in a free flow condition \\ \end{tabular} & \(ANI=\frac{AN}{\Delta N_{0}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Congestion Indexes or Indicators. reliability, caused by users who can generate random content in random places at random times and provide mixed information that is inaccurate. Still, if properly handled, it can be easily combined with conventional information sources. Technologies that provide data collection from connected vehicles [64] and airborne and satellite imagery also belong to area-wide sensors [65; 66; 67]. Based on location of mounting, fixed sensors can be classified into two categories: intrusive and non-intrusive sensors [68]. Intrusive sensors are installed on or in pavement, which include inductive loops, magnetic sensors and piezosensors. Non-intrusive sensors are placed above or next to the road, e.g., on poles or consoles. The main advantages of intrusive over non-intrusive sensors are high accuracy in detecting vehicles and the negligible impact of weather conditions. The main advantages of non-intrusive over intrusive sensors are faster and cheaper installation, often without interruption of traffic flow, and multiple flexible detection zones with most of these sensors. Every technology has its advantages and disadvantages with several characteristics that can affect their effectiveness and suitability for certain purposes: for example, ability to collect traffic flow parameters of interest, accuracy, reliability, price, installation cost, privacy, etc. In Table 3 the main advantages and disadvantages of certain sensors are shown.