The M1 is currently closed after a serious collision on the carriageway.
All lanes are shut northbound between junction 9 for Redbourn and junction 10 for Luton while emergency services deal with the incident.
At about 2pm today two motor vehicles collided on the fourth lane.
Firefighters helped to extract two men in their 80s who were trapped by their injuries.
They were treated by two ambulance crews and an ambulance officer, before being transferred to Luton and Dunstable Hospital for further care.
Long delays are building behind the accident and Herts police have advised motorists to take alternative routes.
The diversion is via the A5, past Markyate, Kensworth and Church End, to the A505/A5/B489 crossroads and onto the A505, re-joining the M1 at junction 11.
The road is not expected to fully reopen until 7pm at the latest.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here