BrickCity: The speedy neighborhood
Why are people going so fast around here?
I often get calls from clients or complaints at cocktail parties about how fast people drive down neighborhood streets—so that became the first BrickCity challenge at our YPT meeting the other night.
There’s several problems with the way most subdivisions lay out their streets these days. Some of them are unavoidable. Many are a real struggle.
Let’s start with the roadway. Most jurisdictions require two lanes at all times and the typical lane width is 12 feet. That starts you out with 24’ of pavement and then 2' on each side for curb and gutter.
There’s a couple of reasons why this is the case. Most cars are 6’ wide, so if you park them on the street, they really need at least 8’ of space. That leaves 16’ left over, which is tight for two cars to navigate, but doable. If there’s cars parked on both sides, traffic will have to yield to pass them, but that’s doable too. It’s also the minimum that most jurisdictions think they need for garbage and fire trucks. They probably don’t need quite that much, but their concerns aren’t unwarranted. Many jurisdictions up north require 32-36’ or more so they have no trouble plowing two full lanes when cars are parked on the street.
So far we’re up to 28 feet. This is not a terrible start and would probably be fine if that was all that was needed and the setbacks aren’t large—but alas, that is not to be the case. Add in a 2’ tree lawn on each side and we’re up to 32 feet (the width of a 10” Lego base plate—One of the nice things about using Lego systems is that you can basically assume each stud is 1’ in width.) Typical sidewalks are usually 5’ but front building setbacks are usually 25-30 feet wide. If they’re parking in their own driveway without blocking the sidewalk, they need at least 19 feet. Assuming a 27’ setback lets me use a green base plate for the front yard and I can put the building right up to the edge with any porches hanging over onto the plate. It also puts me at 96’ between the buildings—which looks really open to the driver if there’s nothing but house and road:
I spent the first 45 minutes of the evening talking about the mental frameworks. I’ve posted enough of that material now that you’ll understand if the visual width is over 90 feet, you’re in trouble in terms of speed. Even with a doorway density of 2 doors for every 100 feet (100’ wide lots) and 600’ block lengths, you’re pushing a 47 mph free flow speed for this scenario—no wonder the neighbors are complaining! Thankfully, people don’t always go that fast on most residential streets, but you can see from the picture above, it’s not out of the question that it could happen, especially if there’s no trees, mailboxes, or on-street parking to break things up visually.
So here is a cross section showing what I gave them to work with:
And here is how they described their plan:
I want to thank Sabrina Viteri, Landon Knoke, Tyler Valila, Jimmy Mai and Laura Eng for their great work on this! Here’s what they ended up with for their cross section:
I think it’s a great start! Dropping the visual width to 25 feet from 96 drops the projected 85th percentile speed to 33 mph instead of 47. If someone is parking on the street, or if they stagger people parking on the street as you go along it, that drops the width to about 14’ wide and the projected speed down to 28 mph, but probably much lower.
I once heard of a street in College Park (a neighborhood in Orlando) that was having problems with cut-through. They got together and agreed to park on the street on alternating sides so that people would have to wind their way through the parked cars. Worked like a charm.
I have my own strategy for dealing with these types of streets, but that description will have to wait for another day.
Later this week, I’ll expand a little on the speed projection formulas. When we tested them, we found several situations where the prediction didn’t line up, but there were good reasons why.