Half Circle Helical Ramp Car Park

Transition

Fig. 4 Ramp «lopes. (Transitions ore required only if romp slope exceeds 10 percent.)

Car Ramp Gradient

occurred leading to a buyers revolt against stretched-out sheet metal, followed by an increase in imports and introduction of domestic compacts Immediately following introduction of United States compacts the car manufacturers began an inching up process until the 05 sq ft compact was 90 sq ft as evidenced in the 1963-1970 "shortest car ' indication.

During the same period the low-price three' began an active 7-year growth period projecting all three into the larger size category Class 120

Ramp Breakover Angle

The ramp breakover angle ia the measure of ability of the car to break over a steep ramp, either climbing or descending, without scraping {see Fig 2), The Society ot Automotive En gineers calls for a minimum of 10 degrees as a design standard. A number of models have not met this standard in recant years. The average for all groups has remained relatively constant during the period 1958-1971 despite appreciable vehicle height reductions.

The ramp breakover angle influence can be altered thru use of design techniques. Transitional blends top and bottom of ramps composed of two or more break points can multiply the ramp steepness, with workable break angles, beyond the normal capacities ot car or driver. In existing structures these problems are overcome by building a pad of asphalt or concrete each side of the break point. In this manner cars having a low breakover angle can negotiate potential critical points without scraping.

Long wheelbase ears combined with low center clearance are most susceptible to inadequate breakover angles Buick Riviera, Pnntiac Tempest, Oldsmobile Toronadn, and Lincoln had lower ramp breakover angles In 1970 than Society of Automotive Engineers design standards recommendation.

Angle of Departure

A reasonable minimum value is necessary to reduce the incidence of tailpipe and rear bump* er dragging. The standard calls for a minimum of 10 degrees, violated only in the 1957-1959 period. Only one 1970 car. Mercury, met the minimum standard. Most cars are substantially above 10 degrees, The most critical condition is at driveways where the apron is steep, or a combination of excessive crown to gutter and apron slope.

Street

Si dewa1k

Exit Drivena y (b)

/^g - No Solid Wall Permitted In This Tri ang1e

Fig. 5 Driveway exits.

Angle of Approach

The trend of approach angle of domestic cars from 1948 to 1962 indicates a drop in the 1957-1959 period below 15 degrees. The stan dard developed in I960 by the Society of Automotive Engineers calls for o minimum value of 15 degrees. The standard has been maintained up to 1970 when reduced by Chrysler and Dodge to 14,0 and 14.6 degrees respectively. (See Fig. 3.)

Ramp Slopes

The maximum ramp slope should be 20 percent. Far slopes over 10 percent, o transition ot least 8 ft long should be provided at each end of the romp at one half the slope of the ramp itself. {See Fig, 4.)

Driveway Exits

A romped driveway exit rising up to o public sidewalk must hove a Iramilion section that is almost level (maximum slope: 5 percent) before intersecting the sidewalk lo prevent the hood of the car from obscuring the driver's view of pedes trians on the walk. This transition should be 16 ft long. ISee Fig, 5a.)

Property line walls should also be regulated so as nol to interfere with the driver's view of pedestrians on a public sidewalk. Wherever art exit driveway is parallel and adjacent to a prop erty line wall which extends all the way to a sidewalk, the edge of the driveway should be physically established, by curb or raiting, at least 6 ft from that wall. For each foot lhat the wall is held bock from the sidewalk, the required distance between driveway and wall may be reduced by one foot. {See Fig. 56.)

RAMP SYSTEMS*

A number of different interfloor ramp systems can be used to enable vehicles to traverse the approximate 10-ft (3-m) elevation between parking levels. Some of these systems provide sepa rale and exclusive ramps, while others make use of continuous sloping floors that accommodate both parked vehicles and interfloor travel.

Ramps may be straight, curved, or a combination. No single ramp system is best for all applications. The choice should be based on site shope and dimensions ond parking demand characteristics. Ramps may be designed for one-way or two-way traffic movement. However, one-lane-wide ramps should nol be operated on a reversible two-way basis.

In some instances, site topography will allow direct access lo several parking levels from the street system. This is a desirable arrangement, since it leaves more space for parking and provides more flexibility for traffic distribution be tween ihe street system and parking facility.

Time and convenience are important to ramp travel ond should be considered in any comparison of ramp types. Actual travel lime on ramps varies little among different ramp system types; however, some ramp systems have more potential for delay caused by conflicting traffic movements thai limit ramp capacity. Other factors influencing ramp design include accident hozords, construction cosl, and ability to accommodate vehicles and drivers conveniently,

Analysis of Ramp Movement»

A ramp system includes any portion of storage floors used by vehicles moving between levels. Nearly every successful ramp system requires vehicles to follow an approximately circular path when traveling between parking levels. The number of 360-degree rotations required to circulate through the garage and parking structure height are major concerns, particularly in self-pork designs.

It is generally desirable to limit Ihe maximum number of complete rotations to five or six. Depending on ramp system type, this will control the maximum desirable number of parking levels and limit the number of parking spaces a driver must pass during garage travel,

Drivers are sometimes distracted or disturbed by the awareness of height when traveling on upper parking levels—a condition that can be accentuated if parking levels extend higher lhan adjacent buildings. To reduce driver distraction.

* Parking Garage Planning and Operation, Eno Foun do Hon tor Transportation, Inc., Westport, Conn., 1978.

parapet walls along driving ramps should be designed to limit the driver's view of surroundings outside Ihe parking structure.

Clearway and Adjacent Ramp Type« Ramp systems may be divided into two types, based on the amount of interference between ramp traffic ond parking unparking operations. Ramp systems designed on the "clearway" principle provide interfloor travel paths completely separated from potentially conflicting parking-unparking move ments. Romp systems in which pari or all of the ramp travel is performed on access aisles may be called the "adjacent parking" type. The number of parking stalls adjacent to the ramp may vary from a smoll number to the lotal capacity of the facility. (See Fig. 1.)

Clearway ramp systems provide the safest movement with least delay and, except for sloping floor designs, are preferred for self-park designs. However, the clearway ramp system is seldom feasible for small garage sites.

An ad|acent-parking layout requires less area per parking stall because of the twofold use of travel paths, and consequently can be used to advantage on smaller land parcels. However, ad jacent-parking ramp designs are more susceptible to traffic movement deloys and potential accident-causing situations.

The actual travel speeds for free moving vehicles on the two types of ramps da not vary greally. Delays on the adjacent-parking type ramp system caused by parking unparking maneuvers are difficult to measure but must be recog nized as a sizeable quantity. Delays will be greater on parking levels nearest the street level, since these levels always have larger numbers of vehicles in Ihe circulation system.

Concentric Versus Tandem Ramp Design Ramp systems also can be classified as concentric or tandem, depending on whether the Irovel paths of vehicles moving up and down between parking levels revolve about the same or separate centers. Helically-curved (spiral) ramps are usually built concentrically to save space and to provide flatter grades. Straight ramp systems are designed in either concentric or tandem configurations.

Vehicles traveling on a ramp system may move either clockwise or counterclockwise. Counterclockwise rotation is generally preferred in the United States and other countries where drivers customarily sit an Ihe left side in vehicles since it places drivers on Ihe inside of turns, enabling better vehicle handling.

Parallel Venus Opposed Ramp Detign For vehicles to rotate in the same direction an a ramp system, up and down ramps must slope in opposite directions, requiring ramp surfaces to be op posed. If up and down ramps slope in the same direction, ramp surfaces are parallel and vehicles must rotate in opposite directions.

While no significant difference has been observed in operational ease, it is obvious that opposed ramp types are safer, since all vehicles must travel in the same direction. Parallel ramp systems are considerably cheaper to construct, however.

Geometric Ramp Types

For safety, convenience, and traffic operating ef ficiency, the path followed by Ihe ramp through traffic on any floor of a parking garage should be short, with minimum turns and traffic crossings. Ramp arrangements within a garage should be consistent, in order to be as simple and compre hensible as possible.

Ramp design and arrangement are influenced by (1) orientation of romp traffic flow to main-floor street entrance and exit points and to other ramp systems that might exist in larger garages, (2) conformance of ramps with access aisles throughout each floor orea, and (3) site dimensions.

Straight-Ramp Syitems Ramps within a straight ramp system usually should be "stacked" one over another for construction economy and traffic circulation uniformity. The stacking of ramps creates a "ramp-well." From a plan view, the sum of Ihe system's ramp-well areas and the floor area containing aisles used by romp portal-lo-portal traffic is the ramp system's area, or envelope. This extends vertically through the parking structure (with the possible exception of roof and/ or basem®ni levels).

For straight-ramp garages, the ramp system is usually rectangularly shaped (ignoring curved ramp ends), with Ihe ramp well(s) along the structure's longer-side dimension. This is because more horizontal distance is required to satisfy ramp grade criteria than to accommodate vehicular movement between ramp ends.

Figure 2 illustrates a basic straight-ramp system having a ramp-well on one side only, In ihis system, vehicles follow an elliptical path, most of which is on flat surfaces. Figure 3 is a parallel straight-ramp system, with ramp-wells on two sides of Ihe structure. Turning movements for the up and down ramps are performed in different areas, while the floor travel is performed in a two-way movement along the same aisle. Depending on structure width, the floor travel could be direclionally separated. The systems repre scnted in Figs, 2 and 3 are both very adaptable lo entrance and exit points on the same street.

Figure 4 is an adjacent-parking type opposed straight ramp system. Travel paths for through up ond down movements fall in Ihe same aisle.

Parking Ramp Plans
Fig. 1 Parking garage axamplei that incorporate adjacent-parking ramp systems for traffic entering ond clearway ramp system* for traffic exiting the facilities.

eliminating traffic crossing points. Figure 5 illus-Irates a clearway type opposed straight-romp system. Ends of opposed ramps on the main floor ore pointed in opposite directions, making this type suited to structures with entrance and exit points on separate streets. This design can be adapted lo entrance and exit points on the same street, but requires a 180-degree turn on the main floor—necessitating additional space.

5troight-romp systems are advantageous in relatively narrow buildings. They require less Floor

Straight Ramp Garage Revit
Fig, t Parallel straight-ramp system with ramp-wells on two structure tides.

area than helically-curved ramps and ore simple to construct, particularly in existing structures being converted to porking garages. However, sharp turns, necessary to gel on and off straight ramps, are disadvantages.

Split-Level or Staggered-Floor Systems. The staggered-floor parking garage, invented by Fer nand E. d'Humy, is now generally referred to as a split level garage. It is constructed in two sections, with floor levels in one section staggered vertically by one-half story from those in adjacent sections. Short straight ramps, sloped in alternate directions and separated by the distance required lo easily make a 180-degree turn between ramps, connect the half-stories.

Any combination of straight ramps can be applied to the split level floor systems. Traffic rota tion direction may be the same, in which case the aisles are one-way, thereby reducing conflicts-Turning paths may overlap, requiring less space for the ramp system. Rotation can be provided also in opposite directions, which simplifies ramp construction by hoving up and down ramps on the same plane.

The division between split-level structure halves

Fig. 3 Straight-ramp system with one ramp-well.

Fig. 6 Two-way staggered-floor ramp system.

Fig. 3 Straight-ramp system with one ramp-well.

Car Straight Ramp GuidelineHumy Ramp System

Fig, 5 Clearway-type opposed straight-ramp system.

Fig. 8 This staggered-floor system provides parking on level floors and desirable one-way traffic flow.

Fig, 5 Clearway-type opposed straight-ramp system.

Fig. 8 This staggered-floor system provides parking on level floors and desirable one-way traffic flow.

may be perpendicular to the street or parallel. In the latter case, either the front or back half may be elevated. Split-level floors can overlap os much as 5 to ó ft (1,5 to 1.8 m) ta increase space efficiency and make narrow sites workable,

Figures 6 through 9 illustrate various types of split-level configurations. Figure 8 is the most common type.

Split-level designs are particularly applicable to small, high-cost sites where maximum use of space must be achieved. Construction is relatively simple, and the design fits well on rectangular sites. This system is efficient in terms of Roar space per vehicle parking stall but, like all ramp systems employing adjacent parking, frequent conflicts may arise between circulating traffic and parking-unporking vehicles.

One variation in the split-level system uses three separate sections, with the two end sections at equal elevations and staggered one-half story with respect to the center section (see Fig. 9). Fifty percent fewer turns ore required, thereby reducing travel time. However, vehicles parked on the end sections must be driven an extra half floor when entering or leaving. f"Wrong way" ramp travel is also a greater possibility with this type of design,

Sloping-Floor Systems The sloping fioar parking garage, in its simplest form, contains twa adjacent parking modules tilted in opposite directions, with cross-aisles at each end so lhat vehicles traveling the length of both aisles make o 360-degree turn to move up or down one complete parking level (Fig. 10), Thus, there is no area set aside for ramps in the ordinary sense. The cross-aisles may be sloped or level.

Porking industry experience indicates that the sloping-floor design is well-suited to self-park operations. The relatively flat floor slope (custom arily ranging between 3 and 5 percent) permits comfortable parking and pedestrian walking. Because parking is adjacent to the interfloor circulation system, each entering customer has an oppor

Parkhaus Grundriss Rampe
Fig. 9 Three-level staggered-floor ramp system.
Private Ramp Design Criteria Cars
Fig, 10 Basic sloping-floor concept.

tunity to pork in the first available space. However, the operational problems in adjacent parking can cause congestion during peak outbound movements if clearway-type express ramps are not used.

Floor-to-floor trovel distance is greater in sloping-floor goroges than in other types of ramp garages. However, this is offset somewhat by the opportunity for greater travel speeds due to flat slopes and longer tangents.

For large structures it is desirable to have only part of the floor area sloped, with level floor sections at ends to form cross-aisles. Ramp connections at midpoints of opposite sloping floors permit one way traffic circulation (Fig. 111*. It is possible to achieve one-way traffic circulation in sloping-floor layouts, with parking along aisles on every level, by using two sloping-floor garage units placed end to end* In the level center section where the two units meet, traffic flow con change from up to down and vice versa. This permits flexibility for angled parking, limited only by available site width (Fig. 12),

Helically Curved Ramp Systems The helix [spiral) ramp can be a single surface that permits vehicles to travel on a continuous helical path between parking levels. When two-way traffic is handled on a single helix, the outer lone is used for up movements, since it has a larger radius of curvature and lower grade. Up movements are usually counterclockwise and down movements clockwise.

Helical-ramp entrance and exit points can be located on the same side or opposite sides of the ramp coil. In either case, ramp access points are located direclly above each other on each succeeding floor. Helically curved ramps should be of the clearway type. Examples are illustrated in Figs. 13 and 14,

The double helix system (Fig. 14) uses two helical-path surfaces thai are sloped in opposite directions. One surfoce can be used for up movements, the other for down movements. The two sloping helical surfaces may be separated or they may be interwoven, Vehicle movements for both up and down travel directions ore made in the same direction of rotation. In ihe United States and other countries using left side drive vehicles, counterclockwise rotation is preferred.

Fig. 11 Sloping-floor iystem with crossover ramp of mid-point.
Fig. 12 Double sloping-floor system with mid« point cros*over.

Interwoven double helix systems are popular in tall structures (10 to 12 parking levels) because the number of 360-degree turns can be reduced by using two separated helical surfaces to serve alternate parking levels.

Traditionally, curving ramps are said to be continuous where they provide 360 degrees of rotation between two parking levels. The noncontinu-ous helically curved ramps that provide rotation through 180 degrees are commonly referred to as semicircular—-although this definition is not quite correct, since the curved section is helical in shape.

Helically curved ramps are most often located in corners of rectangular structures to minimize floor-space loss, or they ore located outside the structure when additional site orea is available. Helically curved ramps require more space than Straight ramps, but they can offer better traffic operation by providing gradual turning as compared to sharp turning movements usually required al ends of straight ramps. In addition.

effectively for express exiting.

superelevation ot ends of straight ramps may require undesirable warping of floor areas.

Express Exit Ramps Large parking structures with frequent high-turnover conditions may be served best with an express ramp for one direction of travel—usually for exiting traffic. Express exits can be curved or straight, and are designed always on the clearway principle, providing oneway traffic movement (Fig, 15), They are generally desirable to serve high turnover transient patronage They improve operating efficiency by reducing travel time and conflicts—but may add significantly to structure costs, since they increase the area prorated to each parking space in determinations of space-use efficiency.

Romp Standards

Ramp design parameters governing the acceptability of such ramp features as maximum gradient and minimum radius of curvature have evolved from garage operating experience. The following discussion presents standards generally used by the parking industry.

Ramp Grades Ramp grade (slope] is computed by multiplying floor-to-floor height by 100 and dividing by the ramp length. The difference between ramp length measured along the slope or horizontally is negligible. Grades on curving ramps are measured along the outer ramp pavement edge.

Maximum practical ramp grades are principally limited by safety considerations and the psycho logical effect on drivers, with hill-climbing and braking abilities of automobiles being a secondary factor. Steep ramps slow traffic movement and can be particularly hazardous when wet, requiring drivers to be excessively cautious.

Humy System

Helical ramp systems can often be advantageous for structures situated on odd-shaped sites.

Names Ramps Examples
Fig. 15 Example* of straight and helical express exit ramps*
Maximum Car Parking Ramp Slope

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Responses

  • maddison
    What is the radius of curvature for the parking ramp?
    3 years ago
  • Yonatan
    How to Measure for a Ramp for car?
    2 years ago
  • jan-erik
    What are the turning radii for helix parking garage ramps?
    3 months ago

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