Today's question:

In my community we are experiencing higher levels of redevelopment within and around our historic streetcar commercial centers. This type of development is extremely important to our community’s future, but as redevelopment takes place, our public works department utilizes outdated and suburban type engineering judgment when it comes to an appropriate sight triangle calculation destroying an extreme amount of on-street parking. When we have done research on other community practices on this subject we have found little to no examples of best practice. It’s all over the place and leaves the ultimate decision in the hands of a select few people with an engineering degree.

What can be done to give these redeveloping business centers the infrastructure they deserve to thrive?
— Downtown Dreamer
Sight triangles graphic from the FHWA (source)

Sight triangles graphic from the FHWA (source)

R MOSES' ANSWER:

On-street parking is a great way to slow down cars, protect pedestrians and make access to businesses easy, while avoiding the wasteful, productivity-killing surface lots that occupy so much valuable downtown real estate. In a walkable urban context, reducing the speed of vehicles will not only increase safety for everyone, but also substantially decreases the geometric sight line requirements.

Sometime sight triangles are mis-applied at signalized intersections, restricting parking or other important uses at corners unnecessarily. Add to this the fact that triangles are often ignored by people who park illegally in the triangle area, which results in cars needing to pull forward into an intersection in order to see oncoming traffic, which may endanger pedestrians... In short, triangles are not the best way to keep drivers and pedestrians safe. 

To make street safer in compact, walkable places, it is more effective to provide cues to drivers to expect people walking, parallel parking, etc. than to try to fit in suburban design criteria. Here are some cues that can help slow cars and avoid the need for large sight triangles:

  • Add curb bump-outs, even if only painted, so that there is clear indication of a crossing and the limits of parking if parking is present.
  • Add lighting so that people and vehicles, can be better seen. 
  • If it can be done (state DOT’s and County Road Commissions not withstanding) get the street narrowed and speed limit as low as possible in pedestrian areas so that everyone has a better chance of seeing each other in a timely manner and negotiating safe transit.  

There is also excellent treatment of sight triangles in the NACTO Urban Street Design Guide here.

Best of luck in reshaping your downtown into a safer, more walkable area with on-street parking!

Note: R. Moses is not meant to be professional engineering advice nor should be relied upon as such. Consult your own technical professional before proceeding with your own project.


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