Bicycle Safety Guide and Countermeasure Selection System
Example of a diagonal median opening to break the crossing into two stages. http://www.pedbikeimages.org/ - Dan Burden
Medians are raised barriers in the center portion of the street or roadway that have multiple benefits for bicyclist, motorist, and pedestrian safety; particularly when they replace center, two-way left-turn lanes. Two-way left-turn lanes can create problems for bicyclists and pedestrians as well as opposing left-turn vehicles and may be used as acceleration lanes by some motorists. A median (or median island) helps manage traffic, particularly left-turn movements, and reduces the number of conflict areas. Left-turn bays may be incorporated at specific locations. The restricted access to side streets may also help to reduce cut-through traffic and calm local streets. Raised medians are most useful on high-volume roads. Bicyclist (and pedestrian) access to side streets, transit stops, or shared-use paths should be maintained by providing access pockets through the median.
Another use of median islands and bicycle crossings is to provide a refuge for bicyclists crossing a busy thoroughfare at unsignalized locations where gaps in traffic in both directions are rare. These islands allow bicyclists to deal with only one direction of traffic at a time, and they enable bicyclists to stop partway across the street and wait for an adequate gap in traffic before crossing the second half of the street. When medians are used for bicycle crossings, a refuge width of 10 ft is desired, according to the Colorado Department of Transportation. If a minimum of 6 ft is not available, the bicycle storage area may be angled across the median with bicyclists directed toward oncoming traffic for crossing the second half of the roadway.
If travel lanes are sufficiently narrowed, installation of medians may also help to slow traffic speeds. Trees and other landscaping elements can be added to raised medians as long as they do not restrict visibility. These elements can help change the character of a street and reduce speeds. Raised medians can also improve motorist safety when they replace two-way center turn lanes; however, desired turning movements need to be carefully studied and provided where necessary so that motorists are not forced to travel on inappropriate routes, such as residential streets, or make unsafe U-turns.
Continuous raised medians are not always appropriate. In some cases, separating opposing traffic flow and eliminating left-turn friction can increase traffic speeds by decreasing the perceived friction of the roadway. Raised medians may also take up space that can be better used for wider sidewalks, bicycle lanes, landscaped buffer strips, or on-street parking, and may cause problems for emergency vehicles. In some environments, raised medians can be constructed in sections, creating an intermittent rather than continuous raised median. Another good alternative device for two-, three-, or four-lane roads is the crossing island, which provides a crossing landing for pedestrians and, in some designs, aids in decreasing vehicle speeds.
Curb extensions may also be built in conjunction with center crossing islands where there is on-street parking. Care should be taken to maintain bicycle access, as bicycle lanes must not be eliminated or squeezed in order to create the curb extensions or islands.
Medians and crossing islands help manage motor vehicle traffic and reduce the number of conflict areas, provide comfortable left-hand turning pockets with fewer or narrower lanes, and may help to slow traffic if roadway is narrowed sufficiently. Providing a protected refuge for bicyclists crossing or making left turns assists bicyclists in crossing high-volume streets at non-signalized locations. Finally, medians and crossing islands provide space for street trees and other landscaping.
The costs for installing a median can vary based on the type of median, the materials, and the scope of the project. Medians will often require grading, excavation, grubbing, and other site preparation activities. These costs are included in the cost information above, but may vary based on the design, site conditions, and whether the median can be added as part of a utility improvement or other street construction project.
Authors and Acknowledgements