| Level of Service | Average Control Delay (sec/vehicle) | Description |
| A | ≤10 | Free Flow |
| B | >10 - 20 | Stable Flow (slight delay) |
| C | >20 - 35 | Stable Flow (acceptable delays) |
| D | >35 - 55 | Approaching Unstable Flow (tolerable delay) |
| E | >55 - 80 | Unstable Flow (intolerable delay) |
| F | >80 | Forced Flow (congested and queues fail to clear) |