Medians can be major amenities for adjacent communities. They have many useful functions including reducing lane widths, providing a safe space for pedestrians as they make their way across the street, split up a lengthy curb-to-curb distance, and becoming a location for trees, flowers, art, and other amenities. They can also present challenges in terms of their design and landscape treatments.
Cross-Section Elements: Medians "Depending on agency practice and specific location requirements, medians may be
depressed, raised, or flush with the surface of the traveled way. Medians should have
a dimension that is in balance with the other elements of the total highway cross
section.". This section describes the different kind of median and their relationship to different kind of road configurations.
Flexibility in Highway Design
Medians: Flexibility in the AASHTO Guidelines The AASHTO Green Book (2) offers considerable flexibility in the use and design of medians.
The Green Book (2) describes operational and safety advantages, provides appropriate widths for
different functions, and discusses tradeoffs. The use of medians is clearly encouraged by the AASHTO Green Book (2). Nothing in the AASHTO Green Book (2), however, mandates the use of medians or their design dimensions. more...
A Guide for Achieving Flexibility in Highway Design
Pedestrian Safety through a Raised Median and Redesigned Intersections
Documentation was done on the effect of a raised median, signalized and redesigned intersections, curbs, and sidewalks on vehicle speed, pedestrian exposure risk, driver predictability, and vehicle volume along a four-lane suburban roadway in central New Jersey. The results are that the 85th-percentile vehicle speed fell by 2 mi/h and pedestrian exposure risk decreased by 28 percent. Also, the median allows pedestrians to cross one direction of traffic at a time and signals, curbs, median, redesigned intersections, and striping patterns work together to manage driver behavior. In regard to vehicles, it was found that vehicle volumes were not affected and that vehicle speeds acted independently of vehicle volumes. A collision analysis projected a savings of $1.7 million over the next three years in direct and indirect costs. The goal of the report was to produce a simple and straightforward analysis tool for similar projects in the area.
-- Michael R. King, Jon A. Carnegie, Reid Ewing
Route 9 Reconstruction New York, NY
After more than 20 years of planning and design efforts, the reconstruction of what was formerly known as the West Side Highway in Manhattan finally began. A proposal originally conceived in the early 1970s for the construction of a six-to-eight lane interstate freeway facility known as Westway, which would have been partly elevated and partly depressed below grade, was withdrawn in 1985. In 1987, the city of New York and New York State established a joint West Side Task Force in an attempt to reach a consensus on what action should be taken to replace the deficient interim highway, and the alternative ultimately was a basic six-lane urban boulevard with three travel lanes provided on either side of a raised, landscaped median. This project shows how a collaborative, multidisciplinary planning and design process, incorporating a high level of continuous public involvement, can result in the creation of a world-class street design and also how detailed investigations of travel demand and traffic movement patterns can result in a dramatic change in the scale of the proposed improvement.
Aesthetic and Safety Improvement, SR-99 Des Moines, WA
The purpose of the project is to improve traffic congestion, operations, and safety; provide facilities for transit and pedestrians; and encourage economic redevelopment along the SR-99 corridor through the city of Des Moines.
University Place, WA University Place, WA
Bicycle lanes on a two-lane road feature a planted median and sidewalk with a green buffer. In some locations, bike lanes are also located next to parking lanes. In just five years, University Place went from no bike lanes to over 40 miles including a new waterfront trail and six bicycle-friendly roundabouts.
Medians and parking islands can have major influence on the character of a byway. Medians can serve to separate opposing traffic, provide a recovery area for out-of-control vehicles, allow space for turn lanes, minimize headlight glare, and provide width for future lanes. Vegetation in the medians gives the road a parkway feel.
Parking islands either physically or visually separate a parking pullout from the traffic lanes. Similar design principles apply to both medians and parking islands. Creative use of vegetation, materials for curbing, and surface treatments for medians and parking islands can complement the byway character.