Expected CRFI by surface & temperature
Surface gives rough CRFI range before any report. Expectations only, not a substitute for actual reading (TC AIM AIR 1.6.7).
| Surface | Expected range (Table 1.5(a)) | Lower limit (Table 1.5(b)) | Upper limit (Table 1.5(b)) |
|---|---|---|---|
| Bare ice | 0.07-0.22 | No limit | 0.3 |
| Bare packed snow | 0.12-0.31 | 0.1 | 0.4 |
| Sanded ice | 0.19-0.35 | 0.1 | 0.4 |
| Sanded packed snow | 0.23-0.47 | 0.1 | 0.5 |
| Dry snow on ice (either depth) | - | No limit | 0.4 |
| Dry snow on packed snow (either depth) | - | 0.1 | 0.4 |
| Dry snow on pavement | 0.16-0.76 (3 mm or less) | 0.1 (either depth) | Dry pavement (either depth) |
- Bare ice tops out at CRFI 0.3; sanded packed snow can reach 0.5.
- Widest range: thin dry snow (3 mm or less) on pavement, because non-uniform coverage lets tires break through to pavement.
CRFI and temperature (Table 1.5(a)):
- CRFI values apply at all temperatures; no measured correlation with surface temperature.
- Exception: near melting point (about 0 degrees C), water film can make surface more slippery than tabulated.
Trap: expected range (Table 1.5(a)) is not the limit pair (Table 1.5(b)); bare packed snow expects 0.12-0.31 but its limits are 0.1 and 0.4.
References
- TC AIM AIR 1.6.7 (CRFI expected by surface: Table 1.5(a), Table 1.5(b))