Some very important things to keep in mind on this matter. This FHWA mandate goes into effect this November and if you read the mandate, as far as EMS and Fire Services are concerned, there are no exceptions.
The wearing of ANSI compliant vests, etc. has become increasingly "standard" since the first draft of the mandate went into effect back in 2006. After November 2008, a clear standard of highway scene safety will be established. I feel that any emergency service that tries to circumvent the new law or bend the law in such a manner as to only wear the vests when certain conditions exist are in my view arrogant and reckless with the safety of their personnel.
Should an EMS, Fire, etc. responder get injured or killed in a mandated highway area and he or she is not wearing an ANSI compliant vest, this could bring very serious litigation against the responder's service. Lack of following standards are what lawyers love to go after.
I've been summonsed to testify in several EMS lawsuits over the years (as a result of my photographs) and I seen very savvy plaintiff attorneys pick apart an accident scene. Some attorneys have even hauled in their own EMS expert witnesses to testify. They go in to win and win they usually do.
As I indicated in my earlier post, I too was almost a victim while photographing an accident scene several years ago and I have since been wearing an ANSI type 3 jacket on ALL MVCs. I hope this new law will be embraced by all emergency services for it's been long overdue.