# Research on Optimization Design of Geometric Parameters of a Novel Frame-Embedded Track (NFET)
## 1 Introduction  
Modern tram belongs to the category of urban rail transit, which is similar to subway and light rails, but at the same time has its own unique technical and operational characteristics and is formed by comprehensive transformation and upgrading, on the basis of traditional tram. As a new type of public transportation, as shown in Figure 1, modern tram has the advantages of large passenger capacity, flexibility, comfort, and novelty, and it is especially suitable for the needs of urban transportation development, with low and medium passenger intensity and environmental sensitivity [1, 2, 3, 4, 5, 6, 7]. Since its application, it has been widely recognized by countries all over the world [8]. At present, modern tram operates in more than 100 cities in about 30 countries in Europe and more than 30 cities in North America, becoming one of the backbone forms of urban public transportation. In recent years, modern tram has also been rapidly promoted in Asian countries, such as China. More than 90 cities in China have planned to build trams, with a planned line mileage of more than 10,000 km. With the popularization and application of the tram system, many scholars have also made theoretical and technological innovations on the structures of tram tracks. The previous studies on tram track structure can be generally divided into three categories: The first category is to study the geometry and mechanical properties of track structure under external load, from the perspective of design and construction. For example, [PERSON] et al. established a finite element model of tram-embedded track with continuous welded rail on a bridge, studied the force and deformation of track structure under temperature load,train load, and braking load, and analyzed the influence of beam temperature difference, line longitudinal resistance, and pier longitudinal stiffness on the expansion-constriction force. The second category is from the perspective of operation and maintenance, in order to study the impact of track diseases on the service performance of track structures [9]. For example, by establishing a 3D nonlinear tram track coupled dynamic model and combining it with the generalized probability density evolution theory, [PERSON] et al. proposed a stochastic analysis model of the tram track coupled dynamic system and studied the stochastic dynamic response of trams at the small radius curved section and the accurate influence of the rail wear amount on running safety [10]. The third category is to study the impact of trams on human production and life, especially focusing on vibration and noise reduction. For example, [PERSON] et al. investigated the impact of tram-induced vibrations on earthquake-damaged buildings in the city of Zagreb, conducted on a tram network scale to identify the critical locations by performing continuous monitoring on the tram network and risk analysis based on the distance of buildings from the track, vibration amplitude at source, and building damage [11]. Most of the existing literature conduct experimental or theoretical research on the basis of the existing tram track structure, but there are few reports on the innovation of track form. Actually, the embedded track structure has gradually become a commonly used track structure for trams, as shown in Figure 2. The conventional embedded ballastless track structure is composed of two independent standard prefabricated rail seats. In the paving adjustment process, they are independent of each other, so they need to be adjusted separately, where the specifications must be ensured, and the gauge should be required. Compared with the slab track structure, the traditional embedded ballastless track greatly increases the time cost and difficulty for the adjustment [12; 13]. In order to improve the efficiency of the track geometry adjustment, we optimized the embedded track structure of the tram and invented a new type of frame-embedded  
Figure 1: Tram and track structure. (**a**) Tram and (**b**) track construction site.