Automated Parking Design considerations – Part 3: Performance, Throughput and Retrieval Time

07/08/17

A major Automated Parking Design Consideration is the system performance. An under-performing system will negatively impact the viability of any real-estate, and so, it is very important to know the development’s parking performance requirements and understand what affects the system’s performance.

System Performance, throughput and retrieval times – which one should I design by?

System performance is measured by the number of storage and retrieval cycles performed over a period of time, for example, 90 vehicles per hour. Performance is typically specified in bi-directional traffic (i.e. Storage and retrieval), and can be specified by detailing the breakdown between storage and retrieval, for example, 60 vehicles Storage (in) and 30 vehicles retrieval (out) per hour.

Throughput is the percentage of the storage and retrieval cycles out of the system parking capacity. For example, a system of 300 parking spaces and a performance level of 90 vehicles per hour is said to have 30% throughput (90/300=0.3).

Retrieval time is the period of time from vehicle retrieval request to delivery of vehicle to driver at the exit compartment (bay room). Retrieval time should be treated with caution as it does not provide any indication to the overall system performance during peak hours. Average retrieval times over a long period of time serve as an indication to the stability of the autonomous parking system

What affects system performance?

Three major factors should be taking into consideration when considering performance:

• System components – each system component (shuttles, lifts, bay rooms) carries a maximal service level, determined by its specifications (travel speed, for example) and process. Service Level is defined in cycles per hour. For example, a lift that performs a full cycle in 40 seconds is said to have a service level of 90 cycles per hour. The system’s bottle-neck, determining the system performance, is defined by the system component type with the lowest combined service level.
• Parking Structure – Physical dimensions of the structure impact the service level of the system components, for example, the horizontal distance a shuttle travels (along with its maximal speed) will determine its cycle time and service level. Another example affecting the same is multi-depth parking. During peak hours, when all system components are operating simultaneously, it is expected that system components will wait for each other to clear pathways, so accordingly, the balance between moving system components and the number of levels and pathways impacts the system performance. Designing an automated parking system with entry/exit bays on multiple levels (or the ability to reach multiple levels) has a positive impact on its performance. We will dedicate one of our future newsletters to this topic.
• Street access and surrounding area – Although not directly related to the system performance capabilities, it is important to consider access routes and surrounding area limitations along with the system performance. It could very well be that the bottleneck of the overall performance is a narrow alley serving as the only access to the AVSRS, or a traffic light with lower service level than the system.