The basic idea of dynamic floating charge is to keep the space occupancy of shared parking facilities within an ideal range. If the occupancy rate is within this range in the current time interval, parking charges remain unchanged in the next time period. If the occupancy rate is below the ideal range in the current time interval, parking charges will be cut a floating step in the next time interval to attract more shared parking demand. If the occupancy rate is higher than the ideal range, parking charges will be raised a floating step in the next period to prevent more shared parking demand. Based on the principle of the dynamic floating space charge method, the upper and lower limits of a floating space are set according to the actual situation. The occupancy rate maintains a relatively stable level through such dynamic adjustment, realizing the effective utilization of idle space resources. Priority parking for the parking lot’s own needs is not affected.
By referring to the parking charge mechanism of San Francisco city, this parking occupancy rate ideal range was set to 60–80%. After determining the occupancy rate as the key indicator, the time interval, the floating step, and upper and lower limits of price floating were determined.
3.2. Floating Charge Process
Based on the space occupancy rate, the process of the dynamically floating charge is as follows:
The parking facilities that are seeking shared spaces are denoted as Y, the parking facilities that open shared spaces are denoted as .
Step 1: Get the shared space–time window of parking facility . Divide the shared space-time window into 15-min intervals and mark them as , for example, represents the first interval after open sharing, and so on.
Step 2: Get the total parking spaces of parking facilities and , recorded as and , respectively. Get the initial parking occupancy and parking charges of parking facility and ; space occupancy rates are denoted as and , respectively; space occupancy are denoted as and respectively; parking charges are denoted as and , respectively; make .
Divide the interval in which the occupancy is located into ,, , , marked as occupancy condition .
Step 3: For the time period, the number of new vehicles arriving at parking facility is ; the number of vehicles leaving parking facilities Y is ; then, the net number of vehicles entering in this period is . If , then proceed to Step 4. Otherwise, the parking facility does not seek shared spaces externally in the time period. Space occupancy is own demand for shared parking facilities .
Step 4: According to the behavior selection model, when the price of the sharing facility and space occupancy conditions of parking facility change, the probability of selecting is calculated. During the time period, when the parking occupancy condition of is , and the price of is , the probability of potential parking users willing to choose is .
Step 5: According to the space occupancy rate of parking facility in the previous time period , calculate the demand to enter the shared parking facility .
If due to the saturation of parking facility , the number of vehicles willing to go to the shared parking facilities is . According to the probability calculation formula (3), the probability of choosing shared parking facilities can be obtained under different saturations and prices.
If , the corresponding space occupancy condition is , which should be discussed in two cases:
First, the net number of entering vehicles during the period plus the number of spaces occupied during the period is still less than or equal to the total number of spaces of the parking facility ; that is, . During time period, the number of vehicles willing to go to the shared parking facilities is , and in this case, .
Second, the net number of entering vehicles during the period plus the number of spaces occupied during the period is more than the total number of spaces of the parking facilities ; that is . There are two parts to demand for the shared parking facilities , one part is demand for when parking facility Y is not saturated, because of the low price or other factors; that is . The other part is the shared parking demand for in the net number of entering vehicles due to the saturation of parking facility ; that is, .Then the driving demand of parking facility S is .
Step 6: Calculate the space occupancy rate and space condition of shared parking facilities in the time period.
According to the driving demand of the parking facility in the time period, the number of departures in the time period is obtained. Therefore, the space occupancy rate of the shared parking facility during the period is obtained; that is , where is the space occupancy of its own demand of the shared parking facilities in the period time, and the space occupancy condition is marked as .
Step 7: Recalculate the space occupancy rate and space conditions of shared parking facilities in the time period.
That is, , and the corresponding space condition is obtained. If , it is no longer necessary to stimulate or suppress the sharing demand by adjusting the price of the parking facility , so the price of the shared parking facility is maintained, that is , otherwise Steps 7 is continued.
Step 8: Adjust the price of shared parking spaces according to the occupancy condition of parking facility in the time period.
When , the space occupancy rate of parking facility S is still less than 60% after open sharing, reduce the price by one step to attract more shared demand, that is .
When , the space occupancy rate of parking facility S is kept within the range of 60–80% after open sharing, there is no need to change the price, that is .
When , the space occupancy rate of parking facility S exceeds 80% after open sharing, increase the price by one step to suppress more shared demand, that is .
Step 9: Repeat Step 3 until the shared space–time window is closed. Complete the floating charge process of sharing space price.
The corresponding flowchart is shown below (
Figure 2).