Ramp Systems
Ramp systems provide the means of access for vehicles from the ground level to the various parking decks. A large numbers of ramp variations exist, including ramps that are designed strictly for vehicle traffic and ramps upon which parking can take place. At representative sample of ramp systems include:
1. Single straight ramp with two-way traffic
All up and down travel takes place on a series of sloping parallel planes, one above the other and wide enough for cars to pass in opposite directions. In a continuous up or down trip, the normal floor driving siales are used to travel between the beginning and ending of each sloping ramp. The ramp width is usually 24 ft with widening at the ends for turning movements. There is no parking or walking on the ramps. Slop is 8 to 10 percent but can be as high as 16 percent. If the slope exceeds 14 percent, a transition slope needs to be introduced to smooth the breakover point. Each ramp climbs the full height of the tier.
2. Two parallel straight ramps, each with one-way traffic
The ramps provide one-way travel, an advantage in an active traffic situation. The separation of the ramps may be advantageous in the basic layout of the building, especially when planning street access points. Requires travel through full length of structure for circulation. Each ramp is usually 12 to 14 ft wide. There is no parking or walking on the ramps. Slope is 8 to 10 percent but can be as high as 16 percent. If the slope exceeds 14 percent, a transition slope needs to be introduced to smooth the breakover point. Each ramp climbs the full height of the tier.
3. Continuous sloping floor ramp with two-way traffic (single helix)
A near continuous rectangular spiral ramp with the slops being 5 to 6 percent. The relative flat slope permits comfortable parking on both sides of the driving aisle “ramps” and does not require the use of additional building site area to be used for inter-floor travel. This economy, together with proven acceptance, makes it an extremely popular design solution. Aisle widths are typical 24 to 25 ft with 90? parking. Each ramp climbs only half the height of the tier.
4. Double sloping floor ramps for one-way traffic (double helix)
Ideal for longer sites, where it is possible to achieve one-way traffic aisles with parking along the aisles on every level. The sloping parking stalls allow easier vehicle access and narrower parking bays. In this configuration, exit flow must travel the full circulation route to exit the structure unless parking spaces are eliminated to allow for occasional cross-over openings where opposing ramps intersect each other. Bay widths can vary from 40 to 60 ft. Structure lengths required typically exceeded 200 ft. Ramp slopes should be designed at 5 percent and not exceed 6 percent. Each ramp climbs the full height of the tier.
5. Double sloping floor ramps with crossover (end- to- end helix)
Two double sloping floor structure units are, in effect, laid out end to end, and in the level center section, where the two units meet, traffic can cross over. This crossover allows exiting traffic to avoid circulating through the entire structure. Bay widths can vary from 40 to 60 ft. Typical structure lengths required would be in the range of 400 ft. Each ramp climbs the full height of the tier.
6. Staggered double sloping floor ramps (double-threaded helix)
Two double sloping floor units are intertwined allowing for crossover traffic at every other floor level. Angled parking is achieved, one-way traffic and the need to travel through the entire structure is avoided while being practical in structure lengths of less than 250 ft. Bay widths can vary from 40 to 60 ft. A very popular arrangement where site dimensions allow. Each ramp climbs the full height of
the tier.
7. Staggered ramp (split level)
Split-level floor construction requires the length of ramp travel to be about one-half the usual inter-floor distance. This was one of the most common designs for years. Split-level floors can overlap as much as five to six feet at the split, which increase space efficiency and makes a narrow site workable. Typically, two ramps are utilized supporting either one- or two-way traffic. Parking and walking does not take place on the ramps. Ramp can be sloped as greatly as 16 percent, but any slopes over 14 percent will require transitions. Each ramp climbs half the height of the tier.
8. Circular or spiral ramps
Typically used in larger parking structures located on sites with additional available space, these are flat surfaced (except for drainage slopes) parking structures similar to a conventional building with one-way spiral ramps leading to and from the parking levels. Such a ramp provides for travel without interference except at the intersections with parking floors. A single-lane spiral has a typical inside curb radius of approximately 30 ft and an outside radius of 41 to 44 ft.
Suggested ramp slopes under ADA requirements are in the range of 5 percent to 6 percent. Non-parking ramps should not exceed 16 percent but preferably not more than 10 percent. If the ramp is greater than 14 percent, a break over transition will be required.