5.1. Discussion
At present, the main stopping schemes of urban rail transit include stop-by-stop trains, express and slow trains and express trains.
In the stop-by-stop train operation scheme, the train stops at all stations. Currently, in addition to a single stop by the stop plan, the stop-by-stop train operation scheme also appears in express and slow trains.
In the express-and-slow train operation scheme, there are one or more express schemes in addition to the stop-by-stop scheme. These express trains only stop at some stations. The express and slow trains work in the following two modes:
When express and slow trains adopt the common track operation, the express train may need to overtake the slow train. At present, in countries that have opened express and slow trains, the main way is to set overtaking stations. When the express train needs to overtake, the slow train stops at the overtaking station and waits. After the express train overtakes, the slow train continues to run.
- (2)
No-overtaking mode
If the express and slow trains adopt the common rail operation without overtaking, it is necessary to adjust the departure interval of the express and slow trains and focus on the running speed of the express train. If the express train might overtake the slow train, slow down or stop it in advance to ensure that the express train in the rear does not overtake the slow train in the front.
There is no stop-by-stop operation scheme for the express train, and several express trains are complementary in order to meet the travel needs of all passengers and ensure that at least one express train stops at the same time between two stations.
This paper compared and analyzed the stop-by-stop train operation scheme, the overtaking scheme of express and slow trains, the no-overtaking scheme of express and slow trains and the express train operation scheme according to the actual situation of Beijing rail transit.
From the perspective of passenger travel time, the longest travel time is required for passengers in the stop-by-stop train operation scheme. In the express-and-slow train operation, only some passengers can reduce their travel time and these passengers are limited to a few lines that express trains can reach. The express train operation scheme can ensure that the travel time of most passengers can be reduced, not just the travel time of short-distance passengers. Therefore, the express train operation scheme is the most efficient way to save passengers’ travel time.
From the aspect of line passing capacity, the stop-by-stop train operation scheme can maximize the layout and drawing of the operation diagram as long as the train between trains does not exceed the minimum safety interval. In the express-and-slow train operation scheme, the total travel time gap between express and slow trains is large, so in the same time interval, the number of trains that can be drawn is reduced, leading to a decline in the line passing capacity. In the express train operation scheme, the difference in total travel time between different types of express trains is much smaller compared with express and slow trains. Therefore, although the number of trains paved may be less than that in the stop-by-stop train operation scheme, it is far larger than the number of express and slow trains. In view of the actual situation of Beijing rail transit, the line capacity during the off-peak period is far greater than the passenger flow demand. Therefore, the express train operation scheme can fully adapt to the current situation of Beijing rail transit.
From the perspective of the operation cost of the operating enterprise, the number of stops in the stop-by-stop train operation scheme is the highest and the number of trains is also the highest because of the long total travel time. Since the turnover time of the express train is reduced, the express-and-slow train operation scheme can reduce the number of stops to a certain extent, which reduces the energy consumption required for train starts and stops and also reduces the number of trains required. However, in the overtaking mode of express and slow trains, an overtaking station needs to be established, which costs a lot. In the no-overtaking mode of express and slow trains, if the line is divided in a common track, a lot of rectification work needs to be carried out to the line. In the express train operation scheme, the number of stops is the least. Moreover, all express trains have the least total turnover time and the minimum number of trains required. Express trains can run on a common track, and no additional planning is required. Therefore, in terms of operating costs of operating enterprises, the express train operation scheme saves the most cost. Combined with the current situation of Beijing rail transit, the conditions are unsuitable to set up overtaking stations on the existing rail transit lines. In addition, the cost is huge. Therefore, the express train operation scheme is feasible for Beijing rail transit.
The results of empirical research show that the express train operation scheme reduces the cost of train starts and stops by 27.78%, which will speed up the operation of trains, improve the operation efficiency of the operating enterprise and reduce the operation cost. After optimization of the express train operation scheme, more than half of the passengers’ travel time will be reduced, the total travel time can be reduced by more than 11%, the unnecessary waiting time can be reduced by more than 57% and the full load rate of the train can be maintained at a more comfortable level. Therefore, the method adopted in this paper can meet the needs of fast travel and enhance the comfort of trains, which will improve the attractiveness of urban rail transit. The model and method proposed in this paper can promote the benign interaction between operators and passengers, provide a theoretical basis for the formulation of public norms of a train operation scheme, make the public norms more scientific and reasonable and promote the development of urban rail transit.
5.2. Conclusions
The train operation scheme is the most critical part of the rail transit operation. A reasonable operation plan can speed up the train turnover, improve the operation efficiency and improve the capacity of the urban rail, thus saving the travel time and cost of passengers, reducing the operation cost of operating enterprises and comprehensively developing the transportation capacity of urban rail transit. In this paper, based on the passenger flow conditions, the express train operation scheme was studied, an optimization model of the express train operation scheme was stablished and a heuristic genetic algorithm was used to solve the model.
Based on the actual passenger flow data of the Changping Line in Beijing, the model was validated and analyzed. From the experimental data, after the operation of the express train operation scheme, the full load rate of the train was maintained at about 60% on weekends and the maximum full load rate of the train in the peak period on Monday also decreased to a certain extent. This can not only enhance the comfort of passengers but also reduce the resource wastage caused by trains. In terms of time, more than half of the passengers can reduce their travel time whether on weekends or Mondays. The total travel time can be reduced by more than 11%, and the unnecessary waiting time can be reduced by more than 57%. From the perspective of operating costs of operating enterprises, the starting and stopping costs of trains can be reduced by 27.78%, which speeds up the operation of trains, improves the operating efficiency of operating enterprises and reduces operating costs. Therefore, the optimization model of the express train operation scheme proposed in this paper is reasonable, feasible and effective and can significantly improve the capacity of urban rail transit, reduce the travel time and cost of passengers and the operating cost of operating enterprises, enhance the attractiveness of rail transit, meet the fast travel needs of passengers and form a benign interaction between operating enterprises and passengers. The model and method proposed in this paper provide a theoretical basis for the formulation of public norms of the express train operation scheme, make it more reasonable and scientific and promote the development of urban rail transit.