University of Virginia Library

LECTURE 13 - PARKING AREAS:

DETERMINING SIZE:

The number of parking spaces to be provided is a function of
carrying capacity...that appropriate number of visitors which can
be accommodated within the inherent capability of a land area to
regenerate itself. The carrying capacity divided by 3.5 visitors
per car will give you a reasonable estimate of the total number of
parking spaces to be provided.

Let's look at a trail within a forested area. Say: the density
of vegetation and the alignment will carry groups of five persons
separated at intervals of not less than 500 feet, and that a closer
interval would detract from the quality of enjoyment of an adjacent
group. The carrying capacity would be the resultant of the
length of the trail (5,000 feet) divided by the interval (500 feet)
multiplied by the number of visitors per group (5 persons) for a
total of 50 persons. Observations show that an additional 25% of
that number will be in the parking area at the same time either
starting to hike or returning from the trail. Parking spaces are
needed for 50 plus 25% (say 12) or 62 persons, divided by 3.5
persons per car for a total of 18 spaces. At 300 SF per car, the
parking area would require 5400 sq. ft. of surface and 180 feet of
curb.

Other standards:

• -Offices for 80 employees and 20 visitors at 1.5 persons/car
  require 67 spaces.

• -Visitor centers for 200 visitors at 3.5 persons/car require
  57 spaces plus staff parking.

• -Swimming beaches at 165 SF/person may require 500 spaces
  located 1,000 feet apart (standard from Griner and
  Associates, used at Assateague Island)

• -Marinas are based on 1¼ acres of water per boat; allow parking
  spaces for one-third the number of rental boat slips

• -Amphitheaters are based on 10 SF/person or 3 LF of seating
  per person

(See the BOR publication on space standards for such things as acres
of open space and recreational facilities for various population
centers.)

Dimensions of Spaces:

The ASLA Construction Handbook shows the following critical
dimensions:

• -45° spaces require 9′x 12′- 9″/car, 49′- 8″ curb to curb, or
  316.7 SF/car

• -60° spaces require 9′x 10′- 5″/car, 56′- 6″ curb to curb, or
  296.6 SF/car

• -90° spaces require 9′/car, 58′- 0′ curb to curb, or 261 SF/car

Even though cars today are smaller, there is need to design for
the standard size automobile. It is my opinion that spaces of ample
size are well worth the extra cost in paving; furthermore, parking
areas of ample size allow two-way circulation thereby overcoming
the need to provide circulatory roads. Howland recommends:

• -90° spaces, 10 feet wide, 60′- 0″ between curbs, or 300 SF/car.

• -For single-rank parking areas, I recommend 45′- 0″ between
  curbs with spaces 10′ wide.

Shade Trees:

I recommend planting a shade tree in every fifth parking space
to cool the temperature inside of cars parked under the canopy.
That provides a maximum spacing of 40′x 50′. The alternative is
planting of trees within the median between the ranks of cars. That
provides a maximum spacing of 40′x 70′. Examine the plan and sections
for the spacing recommended and the alternate.

Willow oak is, as you know, the shade tree I prefer. Pin oaks
are not my choice because of the low habit of branching, though
that species is an excellent tree to screen along the periphery.
American elm is the ideal shape and density if you can justify the
choice in the face of Dutch Elm Disease.

Surfacing:

Crushed gravel chips on a tack coat over a medium type pavement
(i.e. 2″ of surface over 4″ of bituminous concrete, over a 5″crushed
stone base) is adequate for parking areas in urban centers. Avoid
smooth hot asphalt surfaces because leaves tend to make the surface
slippery. Striping is a necessary evil to control density unless
numbered posts are used. Parking meters serve the same purpose in
municipal and commercial areas. I prefer posts.

Drainage:

Curb inlets are more efficient than flush grates located in the
middle of parking areas along the centerline. Part of this prejudice
is based on the observation that pedestrians walk along the centerline,
even though walkways are provided in the median. Leaves tend
to build up over flush grate openings and are better collected in
open throats along the curb than in the middle of the pavement.
Also, consider the fact that noise can result from each car driving
over a loose grate when the inlet is located on the centerline.

Curbs versus Wheelstops:

I prefer cast-in-place concrete curbs (with exposed colored
aggregate) to wheelstops which are precast. In natural areas, I
like stone curbs or pressure treated timber, either dimensioned or
cut from logs. (Don't use extruded asphalt...you know my opinion of
that material.) Wheelstops are frequently fixed to the road surface
with reinforcing steel, a material that is too small in diameter to
resist the impact of the wheels, and so thin that it tends to act
like a knife in cutting the surfacing material. Log and timber
curb (consider ties at 6 x 8) can be imbedded in the surface or
placed on the base before the surface course is applied. Log or
timber has greater resistance to the impacts of car wheels than
wheelstops.

CAUTION!!

The maximum slope on parking areas, in section or profile, should
be 6%!! To exceed that gradient is to invite cars to roll downhill.
Some drivers do indeed forget to set the handbrake or to leave the
car in gear. Also, ice can be a problem in maneuvering into and out
of parking spaces when grades exceed 6%.

SPECIAL CONDITIONS:

Overflow parking areas need not be paved when they are only used
occasionally. Overflow parking areas can be inconspicuous. You
might consider stabilized turf rather than pavement. Lay down eight
inches of #3 stone to grade; puddle the voids with topsoil, then seed
with a deep-rooted grass (Kentucky Bluegrass). Be careful to let
the grade of the topsoil be slightly below the surface of the stone.

Campgrounds:

The most efficient layout I've seen for campgrounds is at Grant
Village, Yellowstone which was built to the criteria recommended by
Frank Mattson, a Park Landscape Architect of outstanding ability.
Frank said that campsites should be staggered along the roadway,
one site per 35 LF of road; that parallel roads should be 125 feet
between centerlines, and that a two-way throat should connect the
one-way loop with the main campground road. Also, that three types
of sites should be provided in equal proportions to accommodate
tents, trailers, or RVs: spurs for back-ins, pull-throughs, and
pull-offs. That's what was built and it functions well after 23
years of intense use.

Campground sanitation requires that the distance from the
farthest site to the nearest comfort station will not exceed 300
feet, and that comfort stations should not be placed farther apart
than 600 feet.

Bus Parking:

Let buses be directed to the right in turning into spaces in
order to provide access to the loading door; otherwise the doors
are blocked by adjacent buses in turning to the left. I recommend
a radius of 50 feet to the outside curb, a turning lane of 15 feet
between curbs, parking spaces 12 feet wide, and a stabilized inside
turf shoulder 2 feet wide.

Amphitheaters:

Locate approach roads and parking areas so that head lights are
directed away from, rather than toward, the seating area and projection
screen. Headlights can be distracting nuisances during
after-dark interpretive programs. Provide low-level standards to
light the trail to the parking area after the program is over.

Trailer Parking at Boat Ramps:

The most critical features in the design of public boat ramps
are the width and gradient of the ramp itself. Let the ramp be
40 feet wide and the grade 14%. That width will serve 3 boats at
one time (all boats seem to leave and return at the same hour).
That gradient will permit most boats to float free of a trailer

without submerging the towing vehicle. Also! Provide a surface of
high traction, especially where algae is prevalent! Imagine yourself
a novice driver towing a new boat and trailer. You approach the
shoreline driving toward the ramp; you turn right until you see the
boat and trailer reflected in the mirror on the car door. You then
back toward the ramp, constantly watching the reflection in the mirror,
until your boat and trailer are aligned with the ramp. You slowly
back down the incline until the boat is bouyant. Then you stop, set
the handbrake, turn the engine off, set the parking gear, and leave
the car to unlash the boat from the trailer. After you have secured
the boat to the pier, you drive the car and trailer to the parking
area—they remain there all day.

After a day of fishing, you return to the pier, secure the boat,
and drive the car and empty trailer back to the ramp. This time you
watch the trailer reflected in the mirror, then back down the ramp
until the trailer is submerged. You stop, set the handbrake, turn
the engine off, set the parking gear, and leave the car to load the
boat on the trailer. Then you drive straight up the ramp and away.

All quite complicated in description, but the simplest way I know
to design a ramp and parking area for the boater who uses the place
ten times a year.

Picnic Areas:

Most of us would prefer to find a table and fireplace ten feet
from the trunks of our cars. Others prefer to carry their picnic
baskets to a secluded spot a hundred yards away. And there are groups
of children who alight from school buses, then rush to the playfield
and later assemble under a shelter for a group picnic. A well-designed
picnic area will satisfy all of those visitors. Locate
the road to serve the sites rather than the sites to fit the road.
Allow 15 sites to the acre in forested areas and provide comfort
stations in conspicuous places beside the roadway for visitors' convenience
and for easy maintenance. Groups of five parking spaces
staggered along the road with bus parking near the playfield will be
efficient. (The publication, Guide for Highway Landscape and Environmental
Design, shows some suggested layouts for roadside rest areas.
See also the NPS publication Park Structures and Facilities available
in our library.)

Maintenance Areas:

The perpendicular distance between the bay doors of storage and
equipment buildings (or fences) should be not less than 100 feet
to provide turning radius for service trucks and snowplows and some
area to stockpile snow. The paving surface should be dark to melt
snow and smooth enough to be cleaned with a firehose. The pavement
on the approach road and in the yard should be about 3″ of surface
on 4″ of bituminous concrete on 8″ of crushed stone base course.
Drainage inlets should be along the centerline to carry water away
from the buildings and to insure that fuel oil and gasoline spills
will be directed away from stored vehicles and buildings.

Turning Radius:

Large trucks including semi-trailers need an outside turning
radius of 65 feet. They can, by backing-up, maneuver within the
100-foot opening of a maintenance yard. Plot the maneuvers on paper
to locate gas pumps, fences, gates, etc. It is not economical to
design maintenance yards for openings greater then 100 feet. Provide
parking areas for large vehicles and employee cars outside of
the yard.

Buses and two-axle trucks need an outside turning radius of
50 feet; plot their maneuvers on paper, too.

Standard-size automobiles need an outside turning radius of
28.5 feet; it is necessary to plot their maneuvers as you do for
buses and trucks.

Treat Ambulances, Firetrucks, and Service vehicles according to
dimensions shown above.