The intersection of 2 major streets can act as both a barrier and a node. Redesigning major intersections requires designers to critically evaluate the tools and tradeoffs available to make an intersection work better for everyone. While shorter cycle lengths, compact design, and pedestrian safety islands are all desirable components of a multimodal intersection, the tradeoffs inherent in each make these difficult to achieve simultaneously. Weigh intersection geometry, signal timing, and traffic volumes to formulate a design that clarifies the hierarchy of street users, while enhancing the safety and legibility of the intersection.
Existing Conditions
1Large intersections like that shown above are often over designed and difficult for both motorists and pedestrians to manage. Channelized right turns and other features create unsafe, highspeed turns.
Evaluate whether or not all travel lanes are absolutely necessary through corridor analysis, and assess the impact of removing a lane in the traffic network.
At large intersections, bicyclists and pedestrians suffer from long exposure times and multileg crossings. Cycle lengths of 120 seconds or more and 2-stage crossings further exacerbate delay. Large corner radii and inadequate pedestrian safety islands designed to accommodate highspeed turns fail to convey safety within a busy intersection.
Recommendations
Minimize unused space. Excess pavement increases speed and accommodates driver error. Control speeds by tightly managing the design and spatial layout of intersections. Tighten lane widths and eliminate unnecessary travel lanes, reallocating space for bike lanes and cycle tracks.
2Use leading pedestrian intervals (LPI) to give pedestrians a head start entering the crosswalk. Add pedestrian safety islands where possible and eliminate channelized right-turn lanes to slow turn speeds and create self-enforcing yielding to pedestrians. Provide a right-turn pocket or mixing zone where right turn volumes merit. Minimize speed, especially at turns. Curb extensions, tight corner radii, cycle tracks, and pedestrian safety islands force drivers to navigate intersections cautiously.
3At large intersections, accommodate bicyclists either through full signalization or mixing zones. While a dedicated bicycle signal is generally desirable from a safety point of view, an added signal phase lengthens the overall cycle length and exacerbates delay for all users. Avoid the use of mixing zones or restrict turns where turn volumes are likely to make bicyclists feel unsafe.
4Bicyclist left turns may be facilitated using intersection crossing markings and a 2-stage turn queue box.
Align lanes through an intersection and enforce turning lanes with curb extensions to reduce merging and weaving. Delineate guide markings through intersections to reduce conflicts and guide turning vehicles.
5Consider banning left or right turns where they are problematic or create safety conflicts.
Provide left-turn pockets where frequent left turns are made, retaining a 6-foot pedestrian safety island by reducing the bike lane buffer.
6Minimize delay to transit vehicles using transit signal priority. Determine the transit stop placement based upon the location of major destinations, transfer activity, and route alignment. At signalized and unsignalized intersections, far-side transit stops are preferable. Bus bulbs improve transit travel times and provide a dedicated space for waiting passengers.
Daylight intersections to maximize sight distance. Reduce vehicle speeds to match sight distance, rather than enlarging the intersection or removing obstructions.