隨著社會與經濟活動的快速發展，私人運具的需求與使用量持續增加，然而，道路資源有限，當旅運需求在特定時段高於道路容量時，往往導致交通擁擠與空氣汙染等問題。在臺灣，特定路段與時段經常發生嚴重的交通擁擠問題，為改善此問題，道路主管機關已先後施行不同的交通管理措施，然而仍無法有效解決上述問題。在道路交通管理措施中，因應交通擁擠而對不同道路用路人徵收不同費率的道路(擁擠)定價策略，已在世界各地廣泛的實施，並且被視為有效改善交通擁擠的方法之一。
不同車種通常具備不同的特性，導致內部與外部旅行成本的差異，進而影響用路人的旅次規劃與路徑選擇行為。因此，在實施道路擁擠定價時，應針對不同車種的特性與其對於整體社會成本之影響，制定相對應的差別費率水準，才能使交通擁擠的外部性適當的內部化，進而減少道路交通需求，有效改善道路交通擁擠問題。
本研究藉由邊際成本定價法探討不同車種之差別定價問題，實證研究以臺灣地區國道五號系統與整體高速公路路網為例，進行相關車流資料的蒐集與模式應用。數值分析結果顯示，國道五號雪山隧道路段的道路通行費，以道路擁擠定價的原理分析，針對目前小型車與大型車所徵收的通行費，平均而言應高於原先價格的兩倍(法定的上限)，此定價可以有效降低交通擁擠，並且將過多的交通流量轉移至替代道路；而國道五號其他多數路段之定價，平均而言則應低於原先價格的兩倍。此外，就整體高速公路路網的數值分析結果顯示，部分路段之擁擠定價高於原先價格的兩倍。 因此，綜合上述兩個不同案例的實證分析結果，國內高速公路的通行費之法定上限應適當的提高，使國道通行費的訂價策略，可以根據不同路段的供需條件，予以適當的調整，以達到社會福利最大化的目標。
最後，本研究在數值分析結果中發現，由於社會福利最大化的目標函數無法確保為凸集合，使得本研究使用的對角法與Frank-Wolfe演算法，在部分情境下無法求得全域最佳解，影響本研究所研提的模式與其求解演算法在實務應用上的可行性，未來研究可以尋求其他求解演算法，以改善本研究之限制。

As the increasing social and economic activities, the demand and usage of private vehicles have been constantly increasing. However, because road capacity is limited, travel demand is periodically greater than road capacity during specific time intervals and road segments, causing traffic congestion and air pollution problems. In Taiwan, severe traffic congestion occurs on specific locations and time periods. In order to mitigate traffic congestion problem, several traffic control and management schemes have been evaluated and/or implemented, but the results are not satisfactory. Among the traffic management strategies, road (congestion) pricing policy which charges specific road users with different characteristics by various tolls have been either tested or implemented around the world, and the results indicate that road (congestion) pricing policy is one of the effective methods to mitigate traffic congestion problems. Generally, different vehicle types have different characteristics that cause varying travel cost in terms of internal and external costs, which in turn influences users’ trip planning and route choice behaviors. Therefore, it is needed to charge differential tolls based on different vehicles’ characteristics and their impacts on the total societal cost. By doing so, traffic congestion external cost could be internalized to a certain extent. Traffic demand could be accordingly reduced, and the ultimate goal of the road pricing policy on resolving traffic congestion problems can be possibly achieved.
This study solves the differential pricing problem by the marginal cost pricing theory under different vehicle types. The empirical study based on the freeway No.5 system and entire freeway network in Taiwan is conducted under different test scenarios. The numerical analysis results indicate that the tolls of passenger car and bus need to be larger than twice of the standard tolls (the ceiling by law) on the Hsuehshan Tunnel segment. The resulted congestion tolls have an effect on reducing traffic congestion and transferring the exceeded traffic flow to alternative routes. Alternatively, for the other segments of the freeway No. 5 system, most resulted tolls are below twice of the standard tolls. As for the test results of the entire freeway system, the numerical analysis results indicate that congestion tolls for partial road segments are above twice of the standard tolls. Therefore, the ceiling by law needs to be relaxed so that the tolling policy can be respectively implemented to achieve the ultimate goal of social welfare maximization.
Finally, this study found that using the Diagonalization and Frank-Wolfe algorithms to solve the road pricing problem is not guaranteed to obtain the global optimal solutions for some cases because the objective function of the proposed social welfare maximization-based marginal-cost pricing model is not convex , which limits the popularity of the proposed congestion pricing model in practical applications. The other solution algorithms need to be pursued to overcome this research limitation.

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