To alleviate traffic congestion in developed small-medium cities like Zhangjiagang, the resident trip selection behaviors of car trip and public transit trip are analyzed based on the collected 1303 questionnaires. Then, it is found that public transit trip sharing rates of residents with and without private cars are both low, although public transit overall satisfaction is quite high, i.e., public transit trip is less attractive because citizens prefer selecting cars in commuting. Furthermore, in consideration of the game process between car trip and public transit trip, improving the public transit attraction becomes an efficient way for reducing traffic pressure in peak hours. Finally, through reviewing advanced experiences in Seoul, Zurich, Nanjing, and Kunshan, and combining these experiences with the investigated resident trip selection behavior characteristics of Zhangjiagang, the public transit priority development support system for small-medium cities is proposed.