This field specifies one of the following assumptions to use when calculating travel time in traffic conditions, shown in the enums below. Depending on the enum chosen, the `duration` field of the TrafficModel response will vary. The value contains the predicted time to destination in traffic, based on historical averages. `TrafficModel` is only available for requests that have set `https://developers.google.com/maps/documentation/routes/reference/rest/v2/RoutingPreference` to `TRAFFIC_AWARE_OPTIMAL` and `https://developers.google.com/maps/documentation/routes/reference/rest/v2/RouteTravelMode` to `DRIVE`.

| Enums ||
|---|---|
| `TRAFFIC_MODEL_UNSPECIFIED` | Unused. If specified, will default to `BEST_GUESS`. |
| `BEST_GUESS` | Indicates that the returned `duration` should be the best estimate of travel time given what is known about both historical traffic conditions and live traffic. Live traffic becomes more important the closer the `departureTime` is to now. |
| `PESSIMISTIC` | Indicates that the returned duration should be longer than the actual travel time on most days, though occasional days with particularly bad traffic conditions may exceed this value. |
| `OPTIMISTIC` | Indicates that the returned duration should be shorter than the actual travel time on most days, though occasional days with particularly good traffic conditions may be faster than this value. |