# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 3 End-Around Taxiways (EATs) around the World
### End-Around Taxivay Classification  
(1) By comparing the layouts of EATs, EATs can be classified into three types: N-type, M-type, and Large N-type, as shown in Table 3.  
Both Type N and Type M are typically used for parallel runways with a medium to close distance between them. Aircraft are usually assigned to use the inboard runways for takeoff and the outboard runways for landing [62]. In some airports, during morning peak periods, both runways may be used for takeoff. In this case, the EAT is utilized to dispatch takeoff aircraft without crossing the active runway. M-type is used for the two or more terminal buildings arranged separately on both sides of the parallel runways and an additional branch on the taxiway between the two runways. Takeoff and landing aircraft can come from either terminal area. The EATs of PEK, SIN, and AMS are referred to as Large N-type in this paper, which is used for the flows between the distant runways (with a distance of more than 760 m). Typically, a main terminal area lies between these runways, and Air Traffic Control (ATC) assigns landing aircraft to the runway nearest to their target gate. However, due to factors like compatibility between runway and aircraft types or the need to maximize runway utilization, aircraft may sometimes land on a runway further from their intended terminal and gate. In such scenarios, utilizing EAT to reach the gate without crossing another  
Figure 7: The land occupation of EATs (ha). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Classification** & **ICAO CODES** & **Characteristics** \\ \hline N-Type & ATL, MIA, DXB, KWE, PKX, MXP, & One or more groups of runways with a distance of less than 760 m. The main terminal building is arranged on one side of a group of parallel runways. \\ \hline M-Type & SHA, DFW, FRA & One or more groups of runways with a distance of less than 760 m. The terminal buildings are arranged separately on both sides of the parallel runways. \\ \hline Large N-Type & AMS, SIN, PEK & One or more groups of runways with a distance of more than 760 m; for aircraft transfer between different terminal areas. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: EAT layouts, classifications, and characteristics. runway improves both runways' efficiency, which is especially crucial for busy airports. Nevertheless, this taxiing method greatly increases both distance and time compared to traditional methods. Therefore, optimizing the taxiway layout through careful design is vital to minimizing taxiing distance and time. (2) Another classification considers the interaction between aircraft operating on EATs and aircraft taking off or landing on the runway that they may go around. Based on this, EATs can be grouped into three types: Back-Around Taxiways (BATs), Runway End-Around Taxiways (REATs), and Start-Around Taxiways (SATs). This approach is preferred in practical planning and design, as it offers clearer operational guidelines for the taxiway system. (a) BATs (Back-Around Taxiways) are positioned behind the runway's takeoff point, ensuring that departing aircraft do not have a visual line of sight with the taxiing plane. The only factor that aircraft on the taxiway need to consider is the potential impact of the jet blast from the departing aircraft. Many airports permit aircraft to cross takeoff runways using entrance taxiways as BATs once departing aircraft have safely taken off or reached a safe distance. This approach necessitates precise spacing between departing flights, leading to additional waiting time. Figure 8 shows the example of typical BAT operation. A BAT can effectively improve operational efficiency with generally lower construction restrictions and costs. BATs located behind the takeoff point of the runway eliminate departure interval restrictions for taxiing aircraft. However, landing aircraft must turn around in the opposite direction to follow the BAT, increasing taxi distance, time, and fuel consumption. Airports such as PKX, MIA, and AMS have implemented BATs, achieving notable safety benefits.