More than 20 Loudoun County public school buses struggled with their morning commutes Friday because of freezing rain and icy roads, highlighting the challenge that school administrators face when deciding when, or whether, to open schools in uncertain weather conditions.

Most of the affected buses were off the roads soon after they first reported trouble — such as skidding or finding their routes blocked by abandoned vehicles, according to schools spokesman Wayde Byard.

Some bus drivers opted to end their routes, and others faced delays as they waited for instructions or safer weather conditions. The last of the buses were off the roads shortly before noon, Byard said, and all students and staff members were safe.

“The bus drivers erred on the side of caution, which we always will,” Byard said. “They’re not going to take risks. We know it’s an inconvenience, but in the name of safety, an inconvenience is just an inconvenience.”

The road troubles occurred on the heels of a record-setting cold snap this week that sent temperatures plummeting into the single digits, prompting numerous local school systems — including those in Loudoun and neighboring jurisdictions in Northern Virginia — to close schools. But not all local districts made the same call; schools in Prince George’s and Arlington counties and Alexandria opened two hours late, and schools in Montgomery County and the District opened at their usual times. The discrepancy prompted some parents to question the rationale used to determine whether to open late or close schools.

Byard said the difficulty faced by Loudoun’s bus drivers Friday shows the complexity of the matter — particularly in such a geographically diverse county, where conditions between the suburban eastern communities and the more rural western areas often vary dramatically.

Loudoun officials announced Thursday afternoon that the school system would open Friday with a two-hour delay, Byard said, but the weather model used to make that decision wound up “stalled a little bit,” he said. “The weather happened later than we first thought.”

Twenty-three of the school system’s fleet of more than 800 buses had difficulty with their morning routes, Byard said. Most were traveling in western Loudoun or attempting to navigate dirt or gravel surfaces — the county has more than 300 miles of unpaved roads, he said.

Loudoun schools were closed Monday and Tuesday because of the unusually cold weather. On the Official Loudoun County Public Schools Facebook page, many parents thanked school officials for erring on the side of safety — but many others decried the decision to close.

“No snow, no rain, no ice. Just cold,” wrote one commenter. “Why is the entire county held hostage by the roads in Western Loudoun?”

“Another bad message sent to our coddled youth,” wrote another.

One parent said it was “a poor excuse” to keep kids home because of the temperature alone. “Since when did the weather need to be perfect to attend school?” he wrote.

Byard said there’s simply no way to make everyone happy. “We get blowback every time we cancel school,” he said. “You’ll never make a perfect decision . . . weather can vary drastically between eastern and western Loudoun.”

Some parents have wondered whether the county could consider zoned closures, but Byard said there are complicating factors — such as teachers who work in eastern Loudoun but live in western Loudoun — that make the prospect unrealistic.

“In the end, it always comes back to safety,” Byard said. “We have to make a risk assessment before we come to school. If a student or staff member is injured in the process, then it wasn’t worth the risk.”