Rules of Thumb for Urban Intersection Design

By Mike Spack, PE, PTOE

In many rural places around the country, an intersection consists of either a stop sign or the constant blinking traffic light in the middle of town.  Usually, no one even pays attention to rules such as yielding to another car or knowing who has the right of way.  People cross the street at random places while waving to you in your car.  You might even see a tractor drive past you.

In urban settings, however, our jobs are much more complex.  We need to engineer for parking, walking, standing, and bicycling in addition to just vehicles.  It’s not a surprise our crash rates are highest at chaotic intersections.

Instead of piling on road signs we wished everyone would read and obey, we need to design intersections so they naturally convey safety for both drivers and pedestrians without a cluster of confusing signs.  Ideally, these intersections deliver acceptable vehicle throughput while keeping bicyclists and pedestrians moving in frigid or rainy weather.

Here are “rules of thumb” for designing healthy urban intersections:

  • Design the intersection to be self-evident to all users
  • Make the intersection as small as possible
  • Align lanes, so the number of approach and departure lanes are equal
  • Square off skewed intersections
  • Manage driver speed, especially turning speed
  • Limit opportunities for drivers to make sudden movements
  • Minimize crossing distances
  • Locate crossings along where pedestrians want to cross
  • Locate crossings and waiting areas within clear sight triangles
  • Organize bus stops to minimize transfer distances
  • Merge cyclists with vehicles at slow speeds and low volumes, separate cyclists from fast speeds and high volumes
  • Prioritize cyclists above turning drivers
  • Ensure sufficient queue space for cyclists
  • Utilize predictable/natural signal phasing
  • Minimize delay for all modes
  • Prioritize signals for pedestrians, cyclists and transit
  • Ensure signal timing works for both commuters and slower walkers
  • Convert non-driving or cycling space to sidewalks or islands
  • Landscape or use sustainable materials for all spaces not used for walking, cycling, or driving

These rules of thumb are from the ITE Journal article, Real Urban Intersection Design, by King and Chellman, which cites the NATCO Urban Street Design Guide.

Are you interested in other intersection designs? Register for our free Traffic Corner Tuesday webinars.

 

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