# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 2 Research Methodology and Literature Review
### Contribution of EAT-Increasing Runway Capacity, Reducing Delay
Figure 2 shows the SHA airport layout; 2-3 aircraft can cross the inner runway simultaneously. As runway capacity approaches saturation, a queue of aircraft often accumulates during takeoff peak periods. Once the preceding aircraft takes off and the runway is clear, the next aircraft in line must promptly enter the runway entrance while others wait for their turn to cross the runway. The limited time window available for crossing calls for close cooperation between air traffic controllers, ground pilots, and airborne pilots. Any delay or disruption in any link may jeopardize the runway capacity for takeoff, thereby increasing the risk of runway incursions [10,11]. To mitigate this risk, a new taxiway construction project was launched, and the North-South EAT started operating in 2021. Compared with February 2019, the flight departure punctuality rate has increased by approximately 15% [52]. Currently, around 70% of total aircraft crossing the runway use the EAT, resulting in an increase in hourly capacity during peak hours by two flights [53]. DFW faced capacity saturation issues earlier than other airports, which led to in-depth studies on the use of EATs. After implementing EATs, DFW compared the change in runway capacity before and after construction using ASDE-X and ADS-B data. The results showed a significant improvement in the hourly takeoff capacity during peak hours by approximately 25% and a decrease in takeoff delays by around 37.8% [41,42]. Before construction, many airports used simulation software to compare the efficiency of EATs. However, it is important to note that different simulation results may not be comparable on the same scale before the implementation strategy of EAT has been determined. Nevertheless, these simulations can demonstrate certain effects of EAT construction. Using a fast-time model, researchers simulated the impact of EAT implementation at Istanbul's new airport, which included plans for six runways with two EATs currently constructed. Comparing the delay conditions with and without EATs, the length of the takeoff queue was significantly reduced during peak hours by using EATs. In three periods, the length of the takeoff queue decreased from 7/20/30 aircraft to 6/9/12 aircraft. Arrival delays decreased by 34%, and takeoff delays decreased by 68% [5]. Similar simulation results were also observed at Pudong Airport. Researchers used Flexsim software to simulate the usage of EATs during peak hours with 23 incoming flights  
Figure 2: Shanghai Hongqiao International Airport (SHA) end-around taxiway and runway cross-taxiway. and an EAT utilization rate of 21.7%. The simulation showed a 3.7% reduction in average taxi time for incoming aircraft during peak hours [21]. This closely spaced parallel runway group has a capacity of 47.59 aircraft per hour under the \"inside takeoff outside landing\" (runway 16R/34L for takeoff and 16L/34R for landing) mode. After using the EAT, the capacity increased to 51.11 aircraft per hour, with an increase rate of 7.40% [54]. This suggests that when runway capacity reaches saturation, relying solely on spacing between taking-off aircraft may not be sufficient to meet the needs of runway crossings, resulting in additional runway occupancy time [55]. The construction of EATs can significantly increase runway capacity and reduce delay times. Therefore, it is recommended that airport master plans include plans for EAT land use for hub airports. However, during the early stages of airport development, the benefits of EATs on runway capacity and efficiency may not be significant, while they are more likely to provide benefits in reducing runway incursions. They can be built at a later stage when capacity growth necessitates them. Drawbacks or Open Challenges--Possible Increase in Detour Distance and Fuel Consumption/Emissions without Conclusive Results  
This paper compares the taxiway length, EAT distance from runway end, and taxing time under different taxiway layouts at ATL, DTW, and DFW.