Improving the safety of level crossings has always been the direction that Taiwan Railways Administration strives for. In the past, the goal was achieved by improving railway-side protective devices; currently, drivers' behaviors of highway users are studied to discover ways to keep illegal trespassing to be the minimum. This study first reviewed past researches about behavior patterns of highway users and fault tree analysis of railway-side protective devices; then, the study developed an integrated fault tree for level crossing crashes in consideration of highway users' behavior patterns. Based on the proposed fault tree, highway-side primary hazard causes at level crossings can be effectively identified. Besides, this study also proposes corresponding improvement strategies and action plans to improve the safety levels of level crossings.