Fatal
Serious
Slight
Uncategorised
| Date | Local Authority | Vehicles | Casualties | Severity |
|---|---|---|---|---|
| Mon 18 Jan 1999 | Harrow | 2 | 1 | Slight |
| Fri 22 Jan 1999 | Watford | 2 | 1 | Slight |
| Tue 26 Jan 1999 | Watford | 2 | 1 | Serious |
| Fri 5 Feb 1999 | Watford | 2 | 3 | Serious |
| Tue 9 Feb 1999 | Hertsmere | 3 | 2 | Slight |
| Thu 11 Feb 1999 | Three Rivers | 2 | 1 | Slight |
| Fri 12 Feb 1999 | Watford | 2 | 1 | Slight |
| Fri 12 Feb 1999 | Watford | 2 | 1 | Slight |
| Sat 13 Feb 1999 | Three Rivers | 2 | 1 | Slight |
| Sat 13 Feb 1999 | Watford | 2 | 1 | Slight |
| Thu 18 Feb 1999 | Watford | 3 | 5 | Slight |
| Sat 20 Feb 1999 | Hertsmere | 2 | 1 | Slight |
| Mon 22 Feb 1999 | Watford | 2 | 1 | Slight |
| Thu 4 Mar 1999 | Harrow | 4 | 2 | Slight |
| Mon 8 Mar 1999 | Harrow | 2 | 1 | Slight |
| Fri 12 Mar 1999 | Harrow | 2 | 1 | Slight |
| Fri 12 Mar 1999 | Hertsmere | 2 | 1 | Slight |
| Mon 15 Mar 1999 | Hertsmere | 3 | 1 | Slight |
| Thu 18 Mar 1999 | Watford | 2 | 1 | Slight |
| Sat 3 Apr 1999 | Three Rivers | 6 | 4 | Slight |
| Fri 9 Apr 1999 | Hertsmere | 2 | 1 | Slight |
| Sat 17 Apr 1999 | Watford | 2 | 4 | Serious |
| Thu 22 Apr 1999 | Three Rivers | 2 | 2 | Slight |
| Thu 22 Apr 1999 | Hertsmere | 2 | 2 | Serious |
| Tue 27 Apr 1999 | Watford | 3 | 3 | Fatal |
| Thu 29 Apr 1999 | Hertsmere | 2 | 1 | Slight |
| Sun 16 May 1999 | Hertsmere | 3 | 1 | Slight |
| Thu 3 Jun 1999 | Hertsmere | 2 | 1 | Slight |
| Wed 9 Jun 1999 | Watford | 2 | 2 | Serious |
| Thu 10 Jun 1999 | Watford | 2 | 1 | Slight |
| Fri 18 Jun 1999 | Watford | 2 | 1 | Serious |
| Tue 6 Jul 1999 | Watford | 2 | 1 | Slight |
| Mon 19 Jul 1999 | Hertsmere | 2 | 2 | Slight |
| Wed 21 Jul 1999 | Hertsmere | 2 | 2 | Serious |
| Mon 26 Jul 1999 | Watford | 2 | 1 | Slight |
| Tue 27 Jul 1999 | Watford | 2 | 3 | Serious |
| Wed 25 Aug 1999 | Three Rivers | 2 | 2 | Slight |
| Wed 25 Aug 1999 | Hertsmere | 2 | 1 | Slight |
| Sat 4 Sep 1999 | Hertsmere | 2 | 1 | Slight |
| Wed 8 Sep 1999 | Hertsmere | 2 | 2 | Slight |
| Sat 11 Sep 1999 | Watford | 2 | 2 | Slight |
| Thu 30 Sep 1999 | Hertsmere | 1 | 1 | Slight |
| Thu 21 Oct 1999 | Watford | 2 | 1 | Slight |
| Sat 30 Oct 1999 | Watford | 3 | 1 | Fatal |
| Wed 3 Nov 1999 | Hertsmere | 1 | 1 | Serious |
| Fri 5 Nov 1999 | Three Rivers | 2 | 2 | Slight |
| Mon 8 Nov 1999 | Hertsmere | 3 | 2 | Slight |
| Sat 13 Nov 1999 | Hertsmere | 2 | 1 | Serious |
| Sat 20 Nov 1999 | Hertsmere | 2 | 1 | Slight |
| Sat 27 Nov 1999 | Three Rivers | 2 | 1 | Slight |
| Mon 29 Nov 1999 | Harrow | 4 | 1 | Slight |
| Fri 3 Dec 1999 | Three Rivers | 1 | 1 | Slight |
| Fri 10 Dec 1999 | Three Rivers | 2 | 1 | Serious |
| Fri 17 Dec 1999 | Hertsmere | 1 | 1 | Serious |