PhillyDaylight: The Philadelphia Daylighting Project

Today, among other large cities in the U.S., Philadelphia has the dubious distinction of having the highest rate of traffic deaths per capita. Nearly half are pedestrians and cyclists; 10% are children. Explore for yourself in this interactive look at crashes in Philadelphia from 2011-2017. 

But counting crashes and fatalities obscures an even more treacherous reality. The number of traffic deaths -- as staggeringly high as it is -- nowhere near covers the unmeasured safety hazards that force people to limit their mobility or simply be afraid to cross the street. What is an unmeasured safety hazard? Consider crossing at an intersection with a stop sign, with a car parked -- legally or illegally -- up to the stop line. A careful adult will step into the street past the parked car, scan and make eye contact with a driver, and hope they will stop*. But children, the elderly, and the mobility impaired can’t manage this nuanced crossing, so they don’t walk outside alone.

The City of Philadelphia has a number of safety initiatives through their Vision Zero program -- named Vision Zero as the goal is to eliminate traffic fatalities. We propose that one of these initiatives should be to daylight all the parking. 

What is Daylighting? Streetfilms has a great introduction video, and SFMTA has a useful article and this picture below.  

A driver has about a 20 degree range of vision (10 degrees on either side, depicted in shaded grey) when in motion approaching stop sign. When cars are parked within this range (noted in the blue), the vision of the driver is significantly restricted.

*Why does this matter when there are STOP signs, and drivers stop at them? To answer this question yourself, stand at an intersection in Philadelphia that is controlled by stop signs only (not traffic lights). You'll notice that some drivers fail to stop! They might roll through the stop sign and only plan to stop if they see a pedestrian. Because of this, it is critical that a pedestrian is visible to a driver.
But can't a driver just move his or her head? Yes, certainly! And careful drivers do, and many drivers are careful. But enough drivers only look straight ahead, plan to roll through the stop sign without stopping, and don't look around for pedestrians. In fact, it's so common for drivers not to stop at stop signs, that some in Philly call this practice, "The Philly Slide". 
​
How far away from a crosswalk should parking be located so drivers can see a waiting pedestrian? 
Before we answer this question, let's look at the regulations. The Pennsylvania Vehicle Code requires that the no-parking zone stretch about 30 feet back from the crosswalk of a stop-signed controlled intersection. Let's see if a 10 degree angle of vision range for a driver would capture a waiting pedestrian. 
​

We'll solve for the angle theta, which represents the angle of vision a driver 30 feet away from the crosswalk  would HAVE TO HAVE to see a waiting pedestrian. If theta is greater than 10 degrees, then we know that the PA Vehicle Code regulation does not ensure safety, and that parking should only be allowed further than 30 feet away from the crosswalk. 

Steps to solve: 
1) Measure, ideally with a flexible table measure, the base and height of the triangle
in our example, a typical South Philly one-way street with parking on both sides, the base is 12 feet and the height is 30 feet

2) Find the hypotenuse of the triangle, h, using the Pythagorean Theorem! 
base^2 + height ^2 = hypotenuse ^ 2
In our example, the hypotenuse^2 = 12^2+30^2 = 144; 144^.5 = 32.3 feet 

3) Use geometry to find Theta
sin Theta = opposite side/hypotenuse
In our example, sin Theta = (12 feet/32.3 feet) = 20.81 degrees

In our example, a driver in a car 30 feet away from the intersection would need to have a ranger of peripheral vision that is 20.81 degrees ON EITHER SIDE (41.68 degrees total) to see a waiting pedestrian! Since a driver only has about 10 degrees of vision on either side, a pedestrian waiting at this intersection would be very hard to see.

PA Vehicle Code needs to be revisited for safety. More than that, many intersections around Philly violate the vehicle code, and have a no-parking zone between the crosswalk and the first parked car that is much shorter than 30 feet. 

Our goals are to: 1) promote understanding of how daylighting can make crossing intersections safer for pedestrians 2) measure how intersections in Philly are doing in terms of providing adequate no-parking zones and put these on an interactive map and 3) encourage the city to daylight parking throughout the city to improve the visibility of pedestrians. 

What can you do? 
We are starting the Philadelphia Daylighting Project to highlight how visible pedestrians are at different stop-sign controlled intersections around Philadelphia. We are asking everyone to measure distances at intersections close by to you around Philadelphia. We will calculate the sight distance required and then map the results. 

Please use the google form to carefully record the intersection, the exact side of the street, the distance of the street crossing from curb to curb, and the distance of the no parking zone (the distance from the middle of the crosswalk to the start of the parking zone). 

V and C measure the distance from the Beginning of the no-parking zone to the Crosswalk.