As more provisions of the Affordable Care Act take effect, children across America whose access to health care has been limited by lack of insurance stand to benefit. But transportation to medical appointments could be a major obstacle that will reduce the impact of Obamacare, according to a letter from children’s health experts printed this month in the Journal of the American Medical Association this month.

Four medical professionals from the Children’s Health Fund write:

Nationally, regardless of insurance status, 4 percent of children (approximately 3 million) missed a health care appointment each year because transportation was unavailable; this includes 9 percent of children in families with incomes less than $50,000. Thirty-one percent later used a hospital emergency department of the health condition associated with that missed appointment.

The authors say rural areas are most affected, and they take a close look at the issue in Mississippi. The team wrote that 66 percent of Mississippi’s counties were at high risk for transportation-related barriers to health care. Of those counties, 13 percent have no access to public transportation and another 87 percent had “limited access.”

But the authors also determine that even in these very rural areas, the distances to be overcome aren’t that overwhelming. Most population centers, they say, are within six miles of a clinic and even “outlying” population centers were generally within 14 miles. That led them to suggest that non-emergency medical transportation provided by hospitals might be warranted if it leads to better health outcomes and reduced emergency room visits. Previous research has found those types of transportation services to be cost effective.