# Quality Behaviour of Turnouts: Comparison, Problem Specification and Recommendation of Measures
## 1 Introduction  
Turnouts play a vital role in railway infrastructure by allowing track changes while the train is in motion. They introduce operational flexibility to an otherwise rigid railway system. Turnouts facilitate the efficient use of infrastructure for planned operations and also allow short-term adjustments in case of interruptions. Consequently, mixed traffic networks typically include a certain number of turnouts, even if they may not be absolutely necessary at all times but are operationally desired. In Austria, the railway network incorporates 13,285 turnouts across a length of 9759 track kilometres, resulting in an average of 1.36 turnouts per kilometre (0.9 for the main network) [1]. The cumulative network of EU27 countries estimates a ratio of 1 turnout per track kilometre, which amounts to approximately 300,000 turnouts within these networks [2]. Due to their technical complexity, operational significance and emphasis on safety, turnouts are expensive assets in the railway system. Network-wide evaluations of life cycle costs (LCCs) in Austria reveal a seventiold difference between the LCCs of one meter of turnout and an equivalent length of an open track [3]. This factor increases to 13 when only considering maintenance costs. In the UK, Cornish reported that the maintenance and renewal costs of turnouts in 2011/2012 amounted to GBP 200 million for maintenance and GBP 189 million for renewal [4]. These figures represent 24% of the total track maintenance budget, despite turnouts accounting for only 5% of the network's total mileage [4]. Regardless of the great importance and costs of turnouts, quality assessments are not as sophisticated as for an open track. Reasons for this are on the one hand the complexity of turnouts [5] and on the other hand the possibility of intensive manual inspection [6]. Since turnouts represent infrastructure that is limited in its longitudinal extent, manual inspection is easier to handle compared to an open track. However, as higher infrastructuredemands are expected in the coming decades due to increased usage [7], and a shortage of track workers are foreseen [8], improvements in data-based quality assessment of turnouts are essential. As for the open track, this assessment starts with track geometry. Track geometry holds great importance as a quality parameter for railway tracks and turnouts [9]. Regulations require the rehabilitation of track geometry when it falls below a certain threshold [10]. This restoration process involves automated techniques such as levelling, lining and tamping, which are relatively cost-effective. However, due to a need for multiple tamping operations over the lifespan of a turnout, absolute costs of tamping constitute a significant portion of the maintenance budget [11]. Poor track geometry not only causes significant correction costs but also indicates suboptimal system behaviour [12]. Deterioration of track geometry depends on the quality/condition of turnout components, interactions between these components and the loading introduced [13]. Through interactions, these parameters are dependent on each other. Negative properties of one of the parameters have a negative effect on the others. Future evaluation methods not only have to indicate turnout sections with poor track geometry behaviour but must additionally search for root causes of poor behaviour [14]. For achieving this aim, every essential component of a turnout must be considered. The most essential components are subsoil, the ballast bed, sleepers and different metal parts. Only by eliminating the cause will symptoms of poor behaviour be eliminated sustainably. Two typical causes of poor track behaviour are problems in subsoil and the ballast bed. A good subsoil is a basic prerequisite for an effective railway system and is therefore also essential for turnouts. Problems with subsoil, for example due to incorrect drainage, lead to disturbed load transfer, resulting in an increased need for maintenance and a reduction in service life.