After assessing the conditions of the roads and sidewalks, many school districts last night decided to close today or open on a two-hour delayed schedule.

Even if most roads were passable, officials erred on the side of safety, noting that sidewalks were still treacherous and large mounds of snow on many corners presented a challenge to schoolchildren and bus drivers.

Gregory Thornton, superintendent of the Chester Upland School District in Delaware County, spent most of yesterday driving the roads of his district. He saw many people walking in the streets rather than the still-unshoveled sidewalks.

"That is no environment for the kids in the morning," he said. The streets, he determined, were not safe for "little ones."

The Philadelphia School District consulted with the Streets Department before making the decision, said Fernando A. Gallard, a spokesman. While primary roads were cleared, the city needed more time for secondary and tertiary streets, he said.

Gallard said that about 80,000 of the district's students walk to school and 55,000 others walk to public buses or trains.

"They have to walk through sidewalks that will very likely not be cleared by tomorrow," he said. Ice on streets and sidewalks was also a concern.

The city's Catholic schools, which rely on public school buses for many students, followed suit and opted to close.

"With historic snowfall, we'll give it one more day to get streets cleared and make it safer," spokeswoman Donna Farrell said.

Officials in many suburban school districts, including Radnor and Haverford in Delaware County, Lower Merion in Montgomery County, and Haddonfield in Camden County, opted for a two-hour delay.

Mary Beth Lauer, spokeswoman for the Haverford Township School District, said snow piles on corners did not leave much room for students.

"It is a safety issue," said Douglas Young, a spokesman for the Lower Merion School District. "We review the roads in our neighborhoods and consider things like passability of sidewalks and whether the ice and snow have been cleared."

While the main roads within the district were fine, many secondary streets still had snow.

"The additional time gives us the ability to get our kids out in a safer manner," Young said.

Contact staff writer Mari A. Schaefer at 610-892-9149 or mschaefer@phillynews.com.