Tuesday, April 19, 2011

PARKING LOT DESIGN IMPLICATIONS

"Surface Parking Limits on the Shelter Capacity of Land" is a more recent post dealing with this issue.



       Parking lots are taken for granted and ignored, but their influence is much greater than their appearance would imply. Fig 1 illustrates the impact of parking lot design decisions on gross building area capacity GBA when various amounts of open space (S’) are included in the lot. Gross building area increments are arranged along the Y-axis. Parking angle increments are arranged along the X-axis. The chart displays the GBA capacity implications of open space decisions within a parking lot for various parking angle configurations. Desirable parking lot open space percentages S’ are a matter for debate, so I’ve included options from 10% to 60%. The GBA results are to be expected, but the performance profiles and GBA ranges are surprising.

FIGURE 1: GBA OPTIONS
Produced by (s) Values Entered in the CG1L Development Capacity Forecast Model




The GBA range in Fig 1 extends from 36,062 sq ft to 66,599 sq ft given the design specification values involved. This will be explained in detail, but Fig 1 should indicate that there is much more to these decisions than appearance; and they will affect our ability to provide shelter capacity within a limited built environment.

I once found that a corporate headquarters building had 50% of its gross building area available for workstations. I don’t recall the average area per workstation, including circulation, but will use 150 sq. ft. Under these circumstances the GBA range forecast in Fig 1 could shelter business activities for 120 to 222 people. This range has many implications including, but not limited to, the potential scope of public revenue generated. Since there is an 85% difference in potential however, this example should indicate the public significance of the ubiquitous parking lot in a complete set of design specification decisions and public regulations. Don’t rush out and pave the town however. Building mass in a sea of pavement does little for our shared quality of life.

If the parking lot provided 1.5 spaces per dwelling unit, and the average gross dwelling unit area were 1,000 sq. ft., the GBA options above would indicate a dwelling unit range of 24 to 44 units. This affects public revenue and private return on investment, but is even more significant to our sustainable future -- if you believe that shelter for growing populations must be contained within limits that protect the functions of our Natural Domain. Balance is critical within this Built Domain however, because building mass and pavement without open space is one option that can reduce our quality of life and its agricultural support. I’ll have more to say, and some equations to offer, in a future essay.

Total parking lot area includes circulation area, parking area and open space (S’). Open space is devoted to landscape islands, miscellaneous furniture and wasted space. Circulation area is function of its one-way or two-way width and the parking space frontage involved. A parking area is equal to the sum of its parking space areas. Open space is calculated as a percentage of the circulation and parking area subtotal. It is added to the subtotal to find the gross parking lot area. In order to calculate these areas, seven values are requested in the design specification template of Table 1.

The data shown in the Table 1 was used to calculate the parking area per space values (s) in the lower forecast panel. For instance, when a 90 degree parking angle and an 8.5 ft. nominal parking space width is considered, an open space provision of 20% is predicted to produce a 36,312 sq. ft. parking area and 363.1 sq. ft. of average parking area per space (s) based on the 100 spaces required. Forecast values for (s) change when the parking angle is modified in Table 1, but examples were produced for 45, 60 and 90 degree parking options. A fourth option was created by changing the bay width to 64 ft. and the two-way circulation aisle width to 24 ft. All (s) values for an 8.5 ft. wide parking space were then summarized in Table 2. A lower value indicates greater efficiency, but an unrealistically low value indicates a lack of maneuverability. The performance profiles in Fig 2 indicate the efficiency of each (s) value produced by the design specification values entered in Table 1.



TABLE 1: PARKING LOT FORECAST MODEL









PARKING LOT DESIGN SPECIFICATION TEMPLATE 









Parking. angle in degrees

90.0




Number of parking spaces required

100




Bay width when pkg angle = 90

66




Useable pad length within pkg space in ft.
20.0




% one-way two-side pkg aisles

0.0%
 enter zero when pkg angle = 90

Two-way circulation aisle width in ft.

26.0




% two-way two-side pkg aisles

80.0%














PARKING LOT PLANING FORECAST in SQ FT 





open space % within pkg area perimeter

perpendicular
bay
one-way
parking
parking
10.0%
20.0%
pkg space
width
aisle
space
aisle




width

dimension
area
area
PLA
area / space
s
PLA
area / space
s









7.0
66
na
14,000
10,920
27,412
274.1
29,904
299.0
7.5
66
na
15,000
11,700
29,370
293.7
32,040
320.4
8.0
66
na
16,000
12,480
31,328
313.3
34,176
341.8
8.5
66
na
17,000
13,260
33,286
332.9
36,312
363.1
9.0
66
na
18,000
14,040
35,244
352.4
38,448
384.5
9.5
66
na
19,000
14,820
37,202
372.0
40,584
405.8
10.0
66
na
20,000
15,600
39,160
391.6
42,720
427.2


















PARKING LOT FORECAST in SQ FT






open space % within pkg area perimeter

perpendicular
pkg space
width
30.0%
40.0%
50.0%
60.0%








PLA
area / space
s
PLA
area / space
s
PLA
area / space
s
PLA
area / space
s









7.0
32,396
324.0
34,888
348.9
37,380
373.8
39,872
398.7
7.5
34,710
347.1
37,380
373.8
40,050
400.5
42,720
427.2
8.0
37,024
370.2
39,872
398.7
42,720
427.2
45,568
455.7
8.5
39,338
393.4
42,364
423.6
45,390
453.9
48,416
484.2
9.0
41,652
416.5
44,856
448.6
48,060
480.6
51,264
512.6
9.5
43,966
439.7
47,348
473.5
50,730
507.3
54,112
541.1
10.0
46,280
462.8
49,840
498.4
53,400
534.0
56,960
569.6


















**Circulation aisles that do not have contiguous parking on a least one side are separately calculated as driveways.



TABLE 2: SUMMARY of (s) VALUES from TABLE 1





S’
parking angle
90-alt bay size
% parking lot open space

45
60
90

(s) values
10
438
400
333
322
20
478
436
363
351
30
517
473
393
380
40
557
509
424
409
50
597
546
454
439
60
637
582
484
468








Fig 1 shows the GBA implications associated with each (s) value calculated. The data for Fig 1 was acquired with the help of the forecast model illustrated by Table 3. Each (s) value from Table 2 was entered in the design specification template of Table 3 to produce a GBA forecast. All other values in the template were held constant to evaluate the GBA influence of each (s) value. The GBA results for a 5 story building were summarized in Table 4 with each corresponding (s) value. These results were charted in Fig 1 to demonstrate the influence of open space components S’ within parking lot efficiency values (s) in terms of their development capacity GBA implications.





DESIGN SPECIFICATION TEMPLATE


Gross Land Area in AC

5.000
data entry
217,800

Public/ private right-of-way & paved easements

0.100
data entry

21,780


Net Land Area

4.500
calculated

196,020

Existing and expansion areas to remain as fraction of GLA

0.200
data entry

43,560


Gross Land Area Reduction
X=
0.300
calculated

65,340

Buildable Land Area Remaining
BLA=
3.500

calculated

152,460

Est. gross pkg. lot area per space in SF
s =
393
data entry



Building SF permitted per parking space
a =
250
data entry




No. of loading spaces
l=
0
data entry




Gross area per loading space
b =
0
data entry

0

Project Open Space as fraction of BLA
S=
0.300
data entry

45,738

Private Driveways as fraction of BLA
R=
0.030
data entry

4,574

Misc. Pavement as fraction of BLA
M=
0.020
data entry

3,049


Loading area as fraction of BLA
L=
0.000
calculated

0

Total Site Support Areas as a fraction of BLA
Su=
0.350
calculated

53,361

Core development area as fraction of BLA
C=
0.650
calculated

99,099

Core development area as fraction of GLA

0.455
calculated

99,099










PLANNING FORECAST 

no. of floors

minimum land area for BCG & PLA

CORE
gross building area
parking lot area
pkg. spaces
footprint
bldg SF / acre
function of BLA


SFAC
flr area ratio
function of BLA


FAR





GBA




PLA 




NPS 




 BCA
FLR









1.00

99,099
38,530
60,569
154.1
38,530
11,009
0.253
2.00


47,828
75,185
191.3
23,914
13,665
0.314
3.00


52,011
81,762
208.0
17,337
14,860
0.341
4.00


54,390
85,501
217.6
13,598
15,540
0.357
5.00


55,925
87,914
223.7
11,185
15,979
0.367
6.00


56,997
89,599
228.0
9,500
16,285
0.374
7.00
NOTE:
Be aware when BCA becomes too small to be feasible
57,788
90,844
231.2
8,255
16,511
0.379
8.00
58,397
91,799
233.6
7,300
16,685
0.383
9.00
58,878
92,557
235.5
6,542
16,822
0.386
10.00
59,270
93,172
237.1
5,927
16,934
0.389
11.00
59,594
93,681
238.4
5,418
17,027
0.391
12.00
59,866
94,110
239.5
4,989
17,105
0.393
13.00
60,099
94,476
240.4
4,623
17,171
0.394
14.00
60,300
94,792
241.2
4,307
17,229
0.396
15.00
60,475
95,067
241.9
4,032
17,279
0.397












FIGURE 2: (s)-VALUES
Produced by the Parking Lot Forecast Model

               

To summarize, (s) values represent the average area provided per space in a parking lot. This includes the open space S’ provided. This average area emerges from a series of design decisions made in Tables 1 and 3. The S’ value influences parking lot efficiency, but at least some must be included to accommodate the functions mentioned. For instance, if a 90 degree parking angle and a parking lot open space provision of 30% is chosen, Table 1 predicts that an 8.5 ft wide parking space will require approximately 393.4 sq ft of total area per space based on all design specification values entered. This value is rounded to 393 in Table 2 and shown at the intersection of the .30 S profile with the 60 degree parking angle in Fig 2. The value is then entered in the design specification template of Table 3. The planning forecast panel in this table predicts that the (s) value entered can support a GBA of 55,925 sq ft when a five story building is considered. This prediction is summarized in Table 4 and can be seen at the intersection of the .30 S profile with the 90 degree parking angle in Fig 1. The relationships shown in Fig 1 should explain why so any buildings float in a sea of asphalt. They should also reveal one reason why developers with insufficient land often seek relief from parking requirements. They cannot compress an (s) value below realistic limits of maneuverability, so other options must be explored when larger GBA values are desired.




TABLE 4: SUMMARY of (s) and GBA VALUES


parking angle
S’
45
60
90
90 alt
pkg open space
s
GBA 5 flrs
s
GBA 5 flrs
s
GBA 5 flrs
s
GBA 5 flrs









10
438
50,768
400
55,055
333
64,686
322
66,599
20
478
46,922
436
50,977
363
59,987
351
61,782
30
517
43,694
473
47,370
393
55,925
380
57,616
40
557
40,815
509
44,320
424
52,267
409
53,975
50
597
38,292
546
41,568
454
49,156
439
50,664
60
637
36,062
582
39,201
484
46,395
468
47,828





































SUMMARY of GBA VALUES

parking angle




S’
45
60
90
90 alt




pkg open space
GBA 5 flrs
GBA 5 flrs
GBA 5 flrs
GBA 5 flrs













10
50,768
55,055
64,686
66,599




20
46,922
50,977
59,987
61,782




30
43,694
47,370
55,925
57,616




40
40,815
44,320
52,267
53,975




50
38,292
41,568
49,156
50,664




60
36,062
39,201
46,395
47,828
















            The average parking lot area provided per parking space (s) is significant to the entire community. It is not simply a question of the maximum development capacity GBA that can be introduced per acre of buildable land area available. This statistic defines intensity, and we all know it can be overdone. Within any project, the parking lot open space S’ provided combines with project open space S to off-set pavement and building mass. Intensity has physical, social and economic implications that affect our health, safety and welfare. To me, welfare means “quality of life”. Its social and economic components are sheltered and served by its physical component. The average intensity of this physical environment must serve our needs but not overwhelm our senses. It must also coexist with a Natural Domain that does not compromise and demands that we respect its privacy. We cannot live without shelter so we must learn more about intensity, because building mass and pavement can overwhelm open space within and beyond any present built environment. Intensity may shelter population growth, but it must also define a sustainable and rewarding quality of life. When successful, the result will be architecture that speaks to the ages with a new level of planning awareness.

Parking lots are part of the issue. They have been considered project open space because they are not building mass that prevents light and air from reaching street level. They do not off-set intensity, however. Building mass and pavement combine to create intensity. This is offset by project open space, which is a defense against excessive intensity that can threaten our quality of life. Project open space S combines with parking lot open space S’ to reduce potential development capacity per acre, or intensity. The conflict is obvious and the future is in question, but excessive intensity is a recipe for stress that ignores the people and their quality of life. The devil is always in the detail, but the ability to accurately forecast options for all affected parties at least makes dialogue, policy and strategy possible. Tactical detail will always require talent to successfully achieve each objective, but tactics without leadership is a blind campaign attempting to reach a sustainable goal.

AUTHOR NOTE: I should have mentioned the obvious from Figures 1 and 2. Gross building area GBA is inversely proportional to the parking lot value (s) when all other values are held constant in a design specification template.