As more and more abandoned railroad beds are converted to rail-trails for bicycles and pedestrians, engineers are facing design problems. Few design guidelines exist for these engineers who typically have not accommodated bicyclists or pedestrians crossing roadways where there are no intersections.

Darren Torbic, a research assistant at Penn State's Pennsylvania Transportation Institute who graduated in January, researched guidelines concerning such crossings for his master's degree project in civil engineering.

The idea to gather this information came to Torbic about a year ago when he was working on a project with the Pennsylvania Department of Transportation. He said PennDOT wanted recommendations to better plan for trail crossings.

The two main guidebooks used in the United States for highway design decisions offer only a few general guidelines for these intersections, he said. So Torbic looked for the specifics. He gathered information from guidelines published in the Netherlands, Finland and the state of California.

Torbic said he compiled information from roughly 20 sources in one document. His paper, "The Planning and Design of Bicycle and Pedestrian Trail Crossings," is about 90 pages long. Previously, design guidelines for intersections were covered in just one or two pages, but Torbic's paper goes into more depth.

"It gives more specific criteria that the designers can use," he said.

His research offers solutions for problems many designers have. For example, because few guidelines exist, many designers do not know what to look for to determine if the crossing will be safe.

One problem designers have is deciding whether the intersection should be on the same plane, called an at-grade crossing, or if the crossing should be grade-separated, using an overpass or tunnel, he said. Through his research, he found when grade separation is warranted.

He also found guidelines specifying when crossings should be marked with crossmarks, and what sight-distances are safest for bicyclists to be able to stop safely if they see something ahead.