The design day and design hour are the demand conditions a parking facility is sized to serve: busy enough to be credible, but not the single busiest hour of the year.
Sizing to the peak hour of the peak day builds stalls that sit empty almost every other day. Sizing to a representative design condition balances customer service against capital cost, and accepts that on a handful of days demand will overflow to other options.
Choosing the design condition
- Rank observed or modeled demand by hour across the year and pick a point near the top, rather than the very top. Roadway engineers often use a similar approach, designing for a high-ranked hour rather than the absolute maximum.
- Match the condition to the use: a retail center may design for a typical December weekend, an office for a typical midweek day, a stadium for a normal game rather than a championship.
- Plan explicitly for the days above the design condition: overflow lots, shared parking, reservations, pricing or shuttles.
- Add an effective supply cushion so the facility works at its design hour without drivers circling for the last space.
The Parkonomics view
Name the day you are designing for, and defend it. The choice of design condition is a policy decision, and it should be written into the study rather than hidden in an assumption.
Related terms: Parking Demand Analysis, Effective Supply, Peak Demand, Shared Parking, Parking Utilization Studies