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.

TABLE 3: DEVELOPMENT CAPACITY FORECAST MODEL
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.