Average annual casualties (2004–2006) per kilometre in low and high casualty 20 mph zones
| Casualty group | Severity | Casualties kilometer (km) | Number of zones* | length of road in zones (km) |
|---|---|---|---|---|
| Low casualty group | Fatal | 0.002 | 169 | 922 |
| Serious | 0.075 | 169 | 922 | |
| Slight | 0.547 | 169 | 922 | |
| Total | 0.624 | 169 | 922 | |
| High casualty group | Fatal | 0.010 | 145 | 844 |
| Serious | 0.205 | 145 | 844 | |
| Slight | 1.443 | 145 | 844 | |
| Total | 1.658 | 145 | 844 |
*Seventy-one 20 mph zones had no casualties in the 3 years before implementation.