Due to recent budget cuts plaguing states and school districts across the country, I definitely see all high school athletics (except maybe the possible money-makers of football, soccer, and basketball) shifting to a club model - totally unaffiliated with the school, where athletes must pay all fees.
In that vein, I would then expect to see XC and track teams be organized as USATF clubs (which are already necessary to run at Nike Team Nationals). USATF actually provides liability insurance to their youth clubs (http://www.usatf.org/clubs/help/FAQ.asp#5), but similar to the maui coach's dilemma, it's got to be in a controlled area:
"Venues: ensure that participants under the age of 18 do not practice on “open” streets (open to vehicular traffic) or any other uncontrolled area – youth practices/training runs must be in a controlled and enclosed area such as track stadium, fenced-in athletic area, etc."
http://www.usatf.org/clubs/application/forms/usatfclubpracticeinsurance.pdf
If you wanted, you could probably interpret a park (or a golf course) as a controlled and enclosed area, such that the running routes don't cross any "open" streets.
But more to maui coach's situation, the biggest liability is runners getting hit by a car. That actually happened to a runner for a coach I know down here in Texas, where the runner actually died. So now he mandates all of his runners wear a reflective sash. Perhaps you could try to convince your administration/school board of the reflective vests/sashes.
Although heaven-for-bid we mandate our runners wear shirts!
http://www.letsrun.com/forum/flat_read.php?thread=4031121&page=0