# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 2 Research Methodology and Literature Review
### Contribution of EAT-Increasing Runway Capacity, Reducing Delay  
EATs are essential in providing a clear path from the runway to the apron. They allow arriving aircraft to cross the runway without having to wait for departing aircraft, enabling a continuous flow of departing aircraft and eliminating the need for runway crossings [9; 44]. Therefore, EAT routing fundamentally reduces the possibility of runway incursions caused by taxiing. By implementing effective EAT routing, airports can ensure efficient and safe aircraft operations while minimizing potential safety hazards. The runway capacity at hub airports is extremely valuable, especially during peak hours when it tends to be saturated [45; 46]. Reducing the runway occupancy time for crossing can further increase the capacity to a certain extent [47; 48]. The controversial issue in constructing EATs based on the assumption of parallel runways with short or medium distances assumes that takeoff intervals meet the crossing demand and no additional departure intervals are required. Therefore, there is no need for a detour, as direct crossing is feasible; the controversial issue is: \"Is the construction of the end-around taxiway still necessary\"? Under certain runway infrastructure conditions, the wake turbulence separation often determines the number of aircraft takeoffs and landings per unit time on the airport runway. Since the wake turbulence separation standards directly affect the operational requirements of the runway, it has become one of the most direct key factors for increasing runway system capacity [49]. Therefore, whether the construction of EATs contributes to the growth of runway capacity depends on the takeoff interval. However, the FAA and ICAO set the approach and landing intervals for countries based on instrument or visual flight and the air traffic control level of the local area. This paper does not conduct in-depth discussions of it, and it only theoretically calculates the crossover times based on the current wake turbulence separation standards at SHA in China. The following example uses SHA to illustrate the timing for landing aircraft to cross the inner takeoff runway: once the departing aircraft has taken off, the air traffic controller issues the crossing command. In cases where there are sufficient crossing paths and no queuing of crossing aircraft, the total time from crossing to leaving the runway impact area is denoted by T. If T is less than the difference between the separation time t\({}_{1}\) of departing aircraft and the time t\({}_{2}\) taken for takeoff, then the crossing time requirement is met [50]. T \(\leq\) t\({}_{1}-\) t\({}_{2}\)  
T: runway occupancy time for crossing; the time it takes for the crossing aircraft to receive the air traffic control instruction and complete the crossing from start to finish. t\({}_{1}\): wake turbulence separation; the separation time between departing aircraft to prevent wake turbulence. A separation time of 2 min is used for this calculation [51]. t\({}_{2}\): takeoff roll time. According to actual measurements and statistics on runways of the same type, the average time required for aircraft of various types to take off from takeoff roll to liftoff is 50 s.  
T = L/V + tr  
L: crossing distance; the calculation takes the distance between two runway holding positions at Hongqiao Airport and uses 190 m as the value. V: crossing taxiing speed is taken as 10 knots. Crossing speed is limited in short distances and is not too fast. Taking 10 knots as the crossing speed is conservative but close to reality. t\({}_{\text{r}}\): startup time, which is the sum of the reaction time of the controller and pilot and the time for the aircraft to start, is estimated to be 30 s based on experience. Taking SHA as an example, the crossing probability is calculated. With a calculated T value of 67 s and a time difference between t\({}_{1}\) and t\({}_{2}\) of only 70 s, this meets the condition for a potential crossing event.