Latency as Distance
Ada re-derives how far a car travels while the network thinks
ADA · CALCULATION AUDIT
Foundations · optional physics
Latency as Distance
At highway speed a self-driving car travels 31.29 m/s (70 mph), so a 10 ms on-device decision passes in just 0.31 m of blind travel while a 100 ms cloud round-trip burns 3.13 m — a 2.82 m gap, more than a car length. The chapter’s latency spectrum already puts autonomous vehicles under 10 ms and calls a 100 ms delay catastrophic. This audit turns that budget into metres and asks whether the edge-versus-cloud choice is settled by the physics of distance rather than by price.
Companion to the chapter Comparing Domain Requirements — every number here comes from that chapter.
Ada's Calculation Audit: latency as distance — how far a car travels while the network thinks, ~3 minutes
A latency budget is really a distance budget. Kinematics turns milliseconds into metres of blind travel, and that is what decides edge versus cloud for a moving vehicle.
The working
1. First convert speed, then apply constant-velocity kinematics. 70 mph × 0.44704 (m/s per mph) = 31.29 m/s.
2. Multiply by each latency. At an edge budget of 10 ms, d = 31.29 × 0.010 = 0.31 m (1.03 ft). At a cloud round-trip of 100 ms, d = 31.29 × 0.100 = 3.13 m (10.27 ft). At 200 ms, d = 6.26 m.
3. The decision is the difference. The extra latency of the 100 ms cloud path over the 10 ms edge path is 3.13 − 0.31 = 2.82 m of travel before the car even begins to react.
| Path | Latency | d = 31.29 m/s × t | Distance |
|---|---|---|---|
| On-device edge | 10 ms | 31.29 × 0.010 | 0.31 m (1.0 ft) |
| Cloud round-trip | 100 ms | 31.29 × 0.100 | 3.13 m (10.3 ft) |
| Slow link | 200 ms | 31.29 × 0.200 | 6.26 m (20.5 ft) |
| Edge advantage | 90 ms | 3.13 − 0.31 | 2.82 m |
What the audit buys you: at highway speed a 90 ms latency difference is 2.82 m — more than a car length of blind travel — which is why the chapter puts collision-avoidance on-device: it is the physics, not the price, that rules out the cloud round-trip.
Every number above is taken from the chapter's own latency-as-distance example and re-derived step by step.