Calculation Methodology
How every Voyrilo result is computed — formulas, data sources, assumptions and known limitations. All calculations are performed server-side; no real-time APIs are used.
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Great-Circle Distance (Haversine)
Used in: Distance, Flight Time, Halfway Point, Cities on the Way
a = sin²(Δlat/2) + cos(lat₁) · cos(lat₂) · sin²(Δlon/2) d = 2R · arcsin(√a) where R = 6,371 km (Earth radius)
All point-to-point distances use the Haversine formula, which computes the shortest path between two points on a sphere (great-circle distance). This is the standard method used by aviation navigation.
Coordinates (latitude/longitude) come from GeoNames (cities) and OurAirports (airports). City coordinates represent the city center; airport coordinates represent the terminal building.
Assumptions
- ✓Earth is treated as a perfect sphere with radius 6,371 km (actual equatorial radius is 6,378 km — error < 0.1%).
- ✓Results are straight-line distances only; actual travel routes are always longer.
Limitations
- ⚠Does not account for terrain (mountains, sea straits) that affect real travel routes.
- ⚠City coordinate precision varies; for large metropolitan areas the center point may be several kilometres from the actual departure point.
Flight Time
Used in: Flight Time, Drive vs Fly
flight_time = (distance_km / 800) + 0.75 hours (800 km/h cruise speed + 45 min overhead)
Flight time is estimated using a cruise speed of 800 km/h (typical for commercial narrowbody aircraft at altitude) plus a fixed 45-minute overhead for taxi, takeoff climb, descent and landing.
This gives a "block time" estimate comparable to what airlines show in search results. Actual block time includes buffer for ATC routing, which varies by region.
For short-haul routes under 500 km, the formula adds 60 minutes overhead instead of 45 to account for a higher proportion of climb/descent relative to cruise.
Assumptions
- ✓Cruise speed: 800 km/h (Mach 0.78, typical for B737/A320 family).
- ✓Ground overhead (taxi + takeoff + landing): 45 minutes for routes > 500 km, 60 minutes for shorter routes.
- ✓No layovers or connections — direct flight only.
Limitations
- ⚠Long-haul widebody aircraft (B777, A350) cruise at 900+ km/h; our estimate is conservative.
- ⚠Headwinds / tailwinds can shift actual times by 10–20% on transatlantic routes.
- ⚠Airport transfer time (city center to airport) is not included.
Driving Distance & Time
Used in: Drive Distance, Cost of Driving, Drive vs Fly, Cities on the Way
road_distance_km = great_circle_km × 1.35 drive_time_hours = road_distance_km / 80 km/h
Road distance is estimated by multiplying the great-circle distance by a factor of 1.35 — the average ratio between road distance and straight-line distance across European routes based on empirical data.
Driving time uses an average speed of 80 km/h, which accounts for a mix of motorway (110–130 km/h), national road (70–90 km/h), and urban sections, plus rest stops.
Cost of driving is calculated as: fuel cost + estimated toll cost + accommodation cost for multi-day trips. Fuel consumption is estimated at 7 L/100 km for a standard petrol car at €1.60/L.
Assumptions
- ✓Road distance factor: 1.35× great-circle (calibrated for European routes).
- ✓Average driving speed: 80 km/h.
- ✓Fuel consumption: 7 L/100 km at €1.60/L.
- ✓Toll estimates: €0.08/km for toll-heavy countries (France, Italy, Spain, Portugal, Greece), €0 for toll-free countries.
- ✓Accommodation: added for trips > 10 hours driving time (€80/night estimate).
Limitations
- ⚠The 1.35× factor is an average; mountain routes or island crossings may have factors of 1.8–2.5×.
- ⚠Fuel prices fluctuate; our estimate uses a fixed European average.
- ⚠Ferry crossings (e.g. channel tunnel, Adriatic ferries) are not included in drive cost.
Airport Transfer Cost
Used in: Transfer Cost, Closest Airport, Alternative Airports
transfer_price = base_rate + (road_distance_km × per_km_rate) Range: min (economy) to max (premium/minivan)
Transfer cost estimates are derived from a price database of 10,000+ historical transfer bookings across 300+ airports and 200+ destinations. The model fits a per-km rate on top of a base rate that varies by origin airport.
We show a range (minimum to maximum) because actual transfer prices depend on vehicle type (sedan vs minivan vs luxury), time of day, and local market competition.
Road distance (not great-circle) is used for pricing, calculated using the 1.35× factor described in the driving section.
Assumptions
- ✓Private transfer (door-to-door), not shuttle or taxi meter.
- ✓Economy sedan as the base vehicle.
- ✓Day-time booking (no late-night surcharge).
Limitations
- ⚠Prices vary with booking platform, season and availability.
- ⚠Local taxi meters may be cheaper for short distances (< 20 km).
- ⚠Book via Transferhood for guaranteed fixed prices.
Carbon Footprint
Used in: Carbon Footprint
CO₂_kg = distance_km × emission_factor Factors (per passenger-km): Flight: 0.255 kg CO₂e (DEFRA 2023, economy) Car: 0.171 kg CO₂e (average petrol, 1.5 passengers) Train: 0.041 kg CO₂e (EU average)
Carbon emissions are calculated by multiplying travel distance by a per-passenger emission factor. Emission factors follow the UK Government DEFRA 2023 greenhouse gas reporting methodology, which is widely used for corporate carbon accounting.
Flight emissions include radiative forcing (RF) at altitude — the actual warming effect of aviation is approximately 2× the CO₂ mass alone due to contrails and high-altitude NOx. Our factor of 0.255 kg CO₂e per passenger-km for economy class already includes an RF multiplier of 1.9.
Tree offsets use an estimate of 21 kg CO₂ absorbed per tree per year (mature broadleaf, IPCC reference).
Assumptions
- ✓Flight: economy class, full passenger load factor (80%).
- ✓Car: standard petrol vehicle, 1.5 average passengers.
- ✓Train: EU average mix (includes diesel regional trains).
Limitations
- ⚠Actual emissions vary significantly with aircraft type, engine age, altitude, and load factor.
- ⚠Electric vehicle emissions depend on national grid mix — our car factor assumes petrol.
- ⚠Carbon offsetting schemes vary greatly in quality; tree planting is illustrative only.
Jet Lag
Used in: Jet Lag
severity = time_zone_diff_hours / 3 recovery_days = ceil(time_zone_diff_hours / 1.5) (eastward travel adds 30% penalty)
Jet lag severity and recovery time are estimated based on the number of time zones crossed. Eastward travel (advancing your clock) is consistently harder to adapt to than westward travel — we apply a 30% penalty for eastward crossings.
The formula is calibrated against published chronobiology research showing approximately 1 day of adaptation per 1.5 time zones crossed (westward) and 1 day per 1 time zone (eastward).
Assumptions
- ✓Standard adaptation rate from published chronobiology studies.
- ✓No sleep aids, melatonin or light therapy interventions.
- ✓Departing at a typical daytime hour.
Limitations
- ⚠Individual variation is high — frequent flyers adapt faster.
- ⚠Short stopovers can shift the effective time zone crossed.