Parking

Lecture notes in Transportation Systems Engineering

3 August 2009

Overview

Parking is one of the major problems that is created by the increasing road traffic. It is an impact of transport development. The availability of less space in urban areas has increased the demand for parking space especially in areas like Central business district. This affects the mode choice also. This has a great economical impact.

Parking studies

Before taking any measures for the betterment of conditions, data regarding availability of parking space, extent of its usage and parking demand is essential. It is also required to estimate the parking fares also. Parking surveys are intended to provide all these information. Since the duration of parking varies with different vehicles, several statistics are used to access the parking need.

Parking statistics

Parking accumulation:  It is defined as the number of vehicles parked at a given instant of time. Normally this is expressed by accumulation curve. Accumulation curve is the graph obtained by plotting the number of bays occupied with respect to time.
Parking volume:  Parking volume is the total number of vehicles parked at a given duration of time. This does not account for repetition of vehicles. The actual volume of vehicles entered in the area is recorded.
Parking load : Parking load gives the area under the accumulation curve. It can also be obtained by simply multiplying the number of vehicles occupying the parking area at each time interval with the time interval. It is expressed as vehicle hours.
Average parking duration:  It is the ratio of total vehicle hours to the number of vehicles parked.

$parking duration= \frac{parking load}{parking volume}$

Parking turnover: It is the ratio of number of vehicles parked in a duration to the number of parking bays available.

$parking turnover= \frac{parking volume}{No. of bays available}$

This can be expressed as number of vehicles per bay per time duration.

Parking index: Parking index is also called occupancy or efficiency. It is defined as the ratio of number of bays occupied in a time duration to the total space available. It gives an aggregate measure of how effectively the parking space is utilized. Parking index can be found out as follows
\begin{displaymath} {\mathrm{parking index}} = \mathrm{\frac{parking load}{parking  capacity}}\times 100 \end{displaymath} (1)

To illustrate the various measures, consider a small example in figure 1, which shows the duration for which each of the bays are occupied(shaded portion). Now the accumulation graph can be plotted by simply noting the number of bays occupied at time interval of 15, 30, 45 etc. minutes ias shown in the figure.

Figure 1: Parking bays and accumulation curve
\begin{figure}\centerline{\epsfig{file=t85-parking-example.eps,width=8cm}}\end{figure}

The various measures are calculated as shown below:

Parking volume= 5 vehicles.

Parking load = $(1+2+1+0+1+2+3+1)\frac{15}{60}$= $\frac{{11}\times{15}}{60}$ = 2.75 veh hour.

Average parking duration = $\frac{2.75 veh hours}{5 veh}$= 33 minutes.

Parking turnover = $\frac{5 veh/2 hours}{3 bays}$= 0.83 veh/hr/bay.

Parking index = ${\frac{2.75 veh hour}{3\times{2} veh hours}}\times{100}$= 45.83%

Parking surveys

Parking surveys are conducted to collect the above said parking statistics. The most common parking surveys conducted are in-out survey, fixed period sampling and license plate method of survey.
  1. In-out survey:  In this survey, the occupancy count in the selected parking lot is taken at the beginning. Then the number of vehicles that enter the parking lot for a particular time interval is counted. The number of vehicles that leave the parking lot is also taken. The final occupancy in the parking lot is also taken. Here the labor required is very less. Only one person may be enough. But we wont get any data regarding the time duration for which a particular vehicle used that parking lot. Parking duration and turn over is not obtained. Hence we cannot estimate the parking fare from this survey.
  2. Fixed period sampling:  This is almost similar to in-out survey. All vehicles are counted at the beginning of the survey. Then after a fixed time interval that may vary between 15 minutes to i hour, the count is again taken. Here there are chances of missing the number of vehicles that were parked for a short duration.
  3. License plate method of survey:  This results in the most accurate and realistic data. In this case of survey, every parking stall is monitored at a continuous interval of 15 minutes or so and the license plate number is noted down. This will give the data regarding the duration for which a particular vehicle was using the parking bay. This will help in calculating the fare because fare is estimated based on the duration for which the vehicle was parked. If the time interval is shorter, then there are less chances of missing short-term parkers. But this method is very labor intensive.

Ill effects of parking

Parking has some ill-effects like congestion, accidents, pollution, obstruction to fire-fighting operations etc.
Congestion: Parking takes considerable street space leading to the lowering of the road capacity. Hence, speed will be reduced, journey time and delay will also subsequently increase. The operational cost of the vehicle increases leading to great economical loss to the community.
Accidents: Careless maneuvering of parking and unparking leads to accidents which are referred to as parking accidents. Common type of parking accidents occur while driving out a car from the parking area, careless opening of the doors of parked cars, and while bringing in the vehicle to the parking lot for parking.
Environmental pollution:  They also cause pollution to the environment because stopping and starting of vehicles while parking and unparking results in noise and fumes. They also affect the aesthetic beauty of the buildings because cars parked at every available space creates a feeling that building rises from a plinth of cars.
Obstruction to fire fighting operations:  Parked vehicles may obstruct the movement of firefighting vehicles. Sometimes they block access to hydrants and access to buildings.

Parking requirements

There are some minimum parking requirements for different types of building. For residential plot area less than 300 sq.m require only community parking space. For residential plot area from 500 to 1000 sq.m, minimum one-fourth of the open area should be reserved for parking. Offices may require atleast one space for every 70 sq.m as parking area. One parking space is enough for 10 seats in a restaurant where as theatres and cinema halls need to keep only 1 parking space for 20 seats. Thus, the parking requirements are different for different land use zones.

On street parking

On street parking means the vehicles are parked on the sides of the street itself. This will be usually controlled by government agencies itself. Common types of on-street parking are as listed below. This classification is based on the angle in which the vehicles are parked with respect to the road alignment. As per IRC the standard dimensions of a car is taken as 5$\times$ 2.5 metres and that for a truck is 3.75$\times$ 7.5 metres.
Parallel parking: The vehicles are parked along the length of the road. Here there is no backward movement involved while parking or unparking the vehicle. Hence, it is the most safest parking from the accident perspective. However, it consumes the maximum curb length and therefore only a minimum number of vehicles can be parked for a given kerb length. This method of parking produces least obstruction to the on-going traffic on the road since least road width is used. Parallel parking of cars is shown in figure 2.
Figure 2: Illustration of parallel parking
\begin{figure}\centerline{\epsfig{file=t32-parallel-parking.eps,width=8cm}}\end{figure}
The length available to park $N$ number of vehicles, L = $\frac{N}{5.9}$
30$^\circ $ parking: In thirty degree parking, the vehicles are parked at 30$^\circ $ with respect to the road alignment. In this case, more vehicles can be parked compared to parallel parking. Also there is better maneuverability. Delay caused to the traffic is also minimum in this type of parking. An example is shown in figure 3. From the figure,

\begin{eqnarray*} AB &= OB sin 30^\circ =& 1.25,\\ BC &= OP cos 30^\circ =& 4.3... ...5,\\ CD &= BD-BC = 5-4.33 =& 0.67,\\ AB+BC &= 1.25+4.33 =&5.58 \end{eqnarray*}

For $N$ vehicles, L = AC + (N-1)CE =5.58+(N-1)5 =0.58+5N

Figure 3: Illustration of 30$^\circ $ parking
\begin{figure}\centerline{\epsfig{file=t34-thirty-degree-parking.eps,width=8cm}}\end{figure}
45$^\circ $ parking: As the angle of parking increases, more number of vehicles can be parked. Hence compared to parallel parking and thirty degree parking, more number of vehicles can be accommodated in this type of parking. From figure 4, length of parking space available for parking $N$ number of vehicles in a given kerb is $L$ = 3.54 N+1.77
Figure 4: Illustration of 45$^\circ $ parking
\begin{figure}\centerline{\epsfig{file=t35-forty-five-degree-parking.eps,width=8cm}}\end{figure}
60$^\circ $ parking: The vehicles are parked at 60$^\circ $ to the direction of road. More number of vehicles can be accommodated in this parking type. From the figure 5, length available for parking $N$ vehicles =2.89N+2.16.
Figure 5: Illustration of 60$^\circ $ parking
\begin{figure}\centerline{\epsfig{file=t37-sixty-degree-parking.eps,width=8cm}}\end{figure}
Right angle parking: In right angle parking or 90$^\circ $ parking, the vehicles are parked perpendicular to the direction of the road. Although it consumes maximum width kerb length required is very little. In this type of parking, the vehicles need complex maneuvering and this may cause severe accidents. This arrangement causes obstruction to the road traffic particularly if the road width is less. However, it can accommodate maximum number of vehicles for a given kerb length. An example is shown in figure 6. Length available for parking $N$ number of vehicles is $L$ = 2.5N.
Figure 6: Illustration of 90$^\circ $ parking
\begin{figure}\centerline{\epsfig{file=t38-right-angle-parking.eps,width=8cm}}\end{figure}

Off street parking

In many urban centres, some areas are exclusively allotted for parking which will be at some distance away from the main stream of traffic. Such a parking is referred to as off-street parking. They may be operated by either public agencies or private firms. A typical layout of an off-street parking is shown in figure 7.
Figure 7: Illustration of off-street parking
\begin{figure}\centerline{\epsfig{file=t73-offstreet-parking.eps,width=8cm}}\end{figure}

Example 1

From an in-out survey conducted for a parking area consisting of 40 bays, the initial count was found to be 25. Table gives the result of the survey. The number of vehicles coming in and out of the parking lot for a time interval of 5 minutes is as shown in the table 1. Find the accumulation, total parking load, average occupancy and efficiency of the parking lot.
Table 1: In-out survey data
Time In Out
5 3 2
10 2 4
15 4 2
20 5 4
25 7 3
30 8 2
35 2 7
40 4 2
45 6 4
50 4 1
55 3 3
60 2 5

Solution

The solution is shown in table 2
Table 2: In-out parking survey solution
Time In Out Accumulation Occupancy Parking load
(1) (2) (3) (4) (5) (6)
5 3 2 26 65 130
10 2 4 24 60 120
15 4 2 26 65 130
20 5 4 27 67.5 135
25 7 3 31 77.5 155
30 8 2 37 92.5 185
35 2 7 32 80 160
40 4 2 34 85 170
45 6 4 36 90 180
50 4 1 39 97.5 195
55 3 3 39 97.5 195
60 2 5 36 90 180
Total 1735

Example 2

The parking survey data collected from a parking lot by license plate method is s shown in the table 3 below. Find the average occupancy, average turn over, parking load, parking capacity and efficiency of the parking lot.
Table 3: Licence plate parking survey data
Bay Time
  0-15 15-30 30-45 45-60
1 1456 9813 - 5678
2 1945 1945 1945 1945
3 3473 5463 5463 5463
4 3741 3741 9758 4825
5 1884 1884 - 7594
6 - 7357 - 7893
7 - 4895 4895 4895
8 8932 8932 8932 -
9 7653 7653 8998 4821
10 7321 - 2789 2789
11 1213 1213 3212 4778
12 5678 6678 7778 8888

Solution

See the following table for solution 4.
Table 4: Licence plate parking survey solution
Bay Time Time  
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
  15 30 45 60 15 30 45 60 Turn over
1 1456 9813 - 5678 1 1 0 1 3
2 1945 1945 1945 1945 1 1 1 1 1
3 3473 5463 5463 5463 1 1 1 1 2
4 3741 3741 9758 4825 1 1 1 1 3
5 1884 1884 - 7594 1 1 0 1 2
6 - 7357 - 7893 0 1 0 1 2
7 - 4895 4895 4895 0 1 1 1 1
8 8932 8932 8932 - 1 1 1 0 1
9 7653 7653 8998 4821 1 1 1 1 3
10 7321 - 2789 2789 1 0 1 1 2
11 1213 1213 3212 4778 1 1 1 1 3
12 5678 6678 7778 8888 1 1 1 1 4
  Accumulation       10 11 9 11  
  Occupancy       0.83 0.92 0.75 0.92 2.25
Columns 1 to 5 is the input data. The parking status in every bay is coded first. If a vehicle occupies that bay for that time interval, then it has a code 1. This is shown in columns 6, 7, 8 and 9 of the table corresponding to the time intervals 15, 30, 45 and 60 seconds.

Summary

Providing suitable parking spaces is a challenge for traffic engineers and planners in the scenario of ever increasing vehicle population. It is essential to conduct traffic surveys in order to design the facilities or plan the fares. Different types of parking layout, surveys and statistics were discussed in this chapter.

Problems

  1. The parking survey data collected from a parking lot by license plate method is shown in table 5 below. Find the average occupancy, average turnover, parking load, parking capacity and efficiency of parking lot.

Table 5: Licence plate: problem
Bay Time
  0-15 15-30 30-45 45-60
1 1501 1501 4021 -
2 1255 1255 1255 1255
3 3215 3215 3215 3215
4 - - 3100 3100
5 1623 1623 1623 -
6 2204 2204 - -

Solution

Refer table 6.
Table 6: License Plate Problem: Solution
Bay Time Time  
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
  15 30 45 60 15 30 45 60 Turn over
1 1501 1501 4021 - 1 1 1 0 2
2 1255 1255 1255 1255 1 1 1 1 1
3 3215 3215 3215 3215 1 1 1 1 1
4 - - 3100 3100 0 0 1 1 1
5 1623 1623 1623 - 1 1 1 0 1
6 2204 2204 - - 1 1 0 0 1
  Accumulation       5 5 5 3  
  Occupancy       0.83 0.83 0.83 0.5  
Column 1 to 5 is the input data. The parking status in every bay is coded first. If a vehicle occupies that bay for that time interval, then it has a code 1. This is shown in columns 6, 7, 8 and 9 of the tables corresponding to the time intervals 15,30,45 and 60 seconds.

Bibliography

Prof. Tom V. Mathew 2009-08-03