Tanker Shuttle Fill-Site-Limited Fleet Size
How many tankers a water shuttle needs before the fill site, not the truck count, is the limit.
Example
You enter
- Usable water per trip (gal) 3000
- Fill-site rate (gpm) 1000
- Dump / unload rate (gpm) 1000
- One-way haul distance (mi) 2
- Average road speed (mph) 35
You get
- Cycle (min) 12.8571
- Fleet to reach the ceiling 5
- Site-limited ceiling flow 1000 gpm
Checked against published worked examples from: IFSTA / NFPA 1142 rural water-supply practice.
Details, formula, and sources
ScopeHow many tankers is enough: past some fleet the water supply stops climbing because the bottleneck is the slowest fixed site, not the truck count. bottleneck = max(tank/fill_gpm, tank/dump_gpm); fleet = ceil(cycle / bottleneck); ceiling flow = tank / bottleneck. A 3,000-gal operation at 1,000 gpm fill and dump over a 2-mile haul needs 5 tankers to reach its 1,000-gpm ceiling; a sixth just queues. Slow the fill to 500 gpm and 3 tankers cap it at 500 gpm - the fix is a faster site, not more trucks. A planning aid, not incident command.
Formula or tablefill_min = tank_gal / fill_gpm; dump_min = tank_gal / dump_gpm; travel_min = 2 x distance_mi / speed_mph x 60; cycle_min = fill_min + dump_min + travel_min; bottleneck_min = max(fill_min, dump_min); fleet_for_max = ceil(cycle_min / bottleneck_min); site_limited_flow_gpm = tank_gal / bottleneck_min.
Source and editionIFSTA / NFPA 1142 rural water-supply fill-site-limited fleet size, by name.
Free accessThe shuttle fleet-size relation is public fire-service / rural water-supply training material; incident command governs the actual operation.
What governsEstimate. AHJ and licensed professional govern.
API field namestank_gal, fill_gpm, dump_gpm, distance_mi, speed_mph, cycle_min, fleet_for_max, site_limited_flow_gpm
- Bottleneck site the sustainable flow caps at tank / max(fill_min, dump_min); the slower fixed site sets itIFSTA / NFPA 1142
- Fleet threshold ceil(cycle_min / bottleneck_min) tankers reach the cap; more just queueIFSTA / NFPA 1142