The following design process takes a sample complex intersection and details how to understand its existing function, analyze its movements, identify opportunities, and create a new design. Driving this process is the underlying need to let land use, community desires, and usage determine solutions.
Existing Conditions
Context
Understand the context within which the intersection functions. Analyze the intersection’s urban-design qualities and document specific gathering places, landmarks, transit stations, and other drivers of activity. Engage the public in this process, allowing safety concerns and community visions to drive the ultimate redesign. Document static conditions, such as:
- Land use
- Property lines and setbacks
- Building footprints, arcades, and courtyards
- Building entrances, façades, and view corridors
- Bridges, tunnels, and unique structures
- Parks, plazas, and public spaces
- Transit stations
- Topography, grading, and stormwater flows
Geometry, Signals, Signs, & Markings
Survey the intersection’s dynamic conditions, or how people are meant to move through the junction based upon existing markings. These elements include:
- Curbs
- Curb ramps and driveways
- Street furniture, plantings, tree pits, benches, and bus shelters
- Centerline of street
- Lane markings: number of lanes, geometry, direction
- Crosswalks
- Stop lines/advanced stop lines
- Traffic signals
- On-street and off-street parking
- Bicycle infrastructure
Vehicle Volumes
Map vehicle movements and turns to understand how motorists are using the intersection. Overlay volume data to illustrate the relative importance of each movement, looking for low volume turning movements in particular.
This process does not need to be data intensive or time consuming. Transportation agencies typically have access to volume and signalization data. Pair this with observation and understanding of the local planning context and how the street fits into the overall traffic network.
Pedestrian Activity
Document how pedestrians use and activate the intersection as a public space. Where are people gathering, sitting, and talking? What activities are they engaged in? Which public spaces attract people and which do not?
Overlay how pedestrians actually move through the junction and the volumes of those movements. Where do people actually cross the street? How many people? In what direction? In this case, a train station is located at the northeast corner of the study area and attracts large volumes of people on foot. In urban locations with continual activity, this step can often be accomplished by 15–30 minutes of observation.
Transit & Bicycle Activity
Assess the volume and movement of cyclists as part of the planned and existing cycling network. Document bus headways and volumes, as well as the placement and location of bus stops.
Signalization
If there is a traffic signal, plot the phases to show how the intersection flows. Obtain phasing data from the appropriate agency, or, if phasing data is not available, the general timing plan can be ascertained with a stopwatch. Note whether pedestrian and vehicle signals are fixed or actuated. Observe how well the phases match volumes, how people comply, and when signals give priority to drivers, cyclists, or pedestrians. Note the tradeoffs made in giving more time or protected signal phases to particular modes or movements. Does adding a protected left-turn phase for vehicles reduce the available crossing time for pedestrians across the side street and encourage crossing against the walk signal?
Redesign
Redesign
Clarity
1Break complex intersections into multiple compact ones. Bend streets so that they meet at as close to a right angle as possible.
Maintain view corridors and sight lines for legibility and wayfinding.
2Mirror turn lanes with curb extensions and medians.
3Align stop lines at all legs of the intersection to be perpendicular to the travel lanes, enhancing overall clarity and visibility for both vehicles and pedestrians.
Compactness
4Minimize intersection size through the addition of curb extensions and medians.
Minimize vehicle turning speeds using medians, realignment, and tight curb radii.
Multi-Modal
5Reallocate space for bicyclists and pedestrians. Widen narrow sidewalks and add cycle tracks.
Realign crosswalks to meet the pedestrian desire line.
Conflict Resolution
Restrict vehicle turns at acute-angled intersections with very low volumes.
6Add median tips at crosswalks.
Consolidate driveways to properties with multiple entry points.
7Close openings in medians that interfere with intersection operations.
Right Sizing
Where traffic-volume data reveals excess vehicle capacity, reduce the number of lanes along a corridor, consolidate excess turn lanes, and eliminate slip lanes. Reallocate space to medians, bicycle infrastructure, or sidewalks.
Public Space
8Utilize excess asphalt from the reconfiguration to create a public plaza. Low-cost materials may be used on an interim basis until full reconstruction and curb relocation. Evaluate the performance of the new configuration and adjust the design as necessary.
Assess and design the entire public realm in a holistic way to create one seamless pedestrian realm. Integrate intersection design elements with the surrounding buildings and plazas. Enhance and take advantage of existing public spaces in the redesign area.
NEW YORK, NY
Unveiled in 2010 as part of a series of major reconfigurations along Manhattan’s Broadway corridor, Union Square embodies the key principles used by NYC DOT in redesigning complex intersections. As part of the redesign, multiphase traffic signals were simplified, pedestrian plazas created at undefined or underused locations, and bikeways and turn lanes added to better accommodate southbound traffic.