現今許多國家正遭遇嚴重的交通擁塞問題所帶來的巨大經濟損失。解決交通擁塞最常用的方法之ㄧ，就是找出擁塞路段並且告知駕駛員迴避此路段。因此，如何有效地偵測出擁塞路段，是目前重要的研究議題。過去的文獻大部分採用定期地於各路段收集行駛於該路段的車輛的平均速度，以此獲取該路段的交通狀況。其實，除了行駛車輛的平均速度，道路上的車輛密度也能反映出實際的交通狀況：車輛密度越高代表交通量越大，擁塞的可能性愈高。因此本論文提出一簡單有效的方法來偵測道路上的車輛密度：發起式車輛密度偵測 (Origination-based Vehicle Density Detection, OVDD) 方法。此一方法週期性地利用車間通訊協定(Inter-vehicle Communication Protocol)廣播訊息，聽到該訊息的車輛便開始進行回報或報數。由於廣播訊息可接收的範圍是固定的，因此我們利用回報的車輛數目，可求得道路上的車輛密度。此外，本論文提出車輛密度-最高平均車速轉換公式並且利用此轉換公式，將車輛密度轉換成最高平均速度。而模擬結果顯示出，OVDD方法能有效的避免車輛行駛於擁塞路段，與考慮路徑長短不考慮交通狀況的方式比較，可大量縮短行駛的旅途時間。 Nowadays many cities have suffered from traffic congestion problems and sustained serious economic loss. One of the most strategies for solving traffic congestion problem is to provide real time information of congestion roads for drivers. Therefore, identifying congestion roads is an important issue. Most of previous approaches used the average speed of vehicles traveling on a specific road section as a measure of traffic congestion. In this paper, we consider another measure of traffic congestion: vehicle density, number of vehicles per unit area of road. Vehicle density can reflect the actual situation of traffic congestion. Vehicle density is higher (lower) as traffic congestion become more (less) serious. We propose an effective scheme to determine vehicle density on the roads, named Origination-based Vehicle Density Detection (OVDD). In the proposed scheme, vehicles are chosen to broadcast initiated messages through Inter-vehicle Communication. Each vehicle which is receiving the message and traveling on the same road section replies a message to the sender. Since the communication range is fixed, vehicle density could be estimated by (the number of replying vehicles)/(communication diameter). In addition, we propose a formula to transform the vehicle density into maximal average speed on the road. The simulation results show that our OVDD scheme can efficiently avoid the vehicles passing the congested roads and the travel time is shorter than the shortest distance scheme.
