DC Speed Limits Data
DEVELOPING
The purpose of DC Speed Limits is to provide a view of the speed limits on DC roadways. This speed limits data is derived (via Python script) from DDOT's GIS sign inventory. Below, we explain how the data are created and also attempt to tackle some of the common questions
How is the DC Speed Limits data created?
Below is a high-level overview of the process to create speed limits.
Query all known sign types which have a MPH value stored. Those types are listed in the table below.
Each sign in Signworks has been associated to the nearest roadway centerline.
- Begin each route with an assumed speed limit of 20 MPH. Sort all the speed limit signs by the route and the measure along the route and also by what side of the road they are on.
- The Python script evaluates each sign on the outbound side and stores the speedlimit in a dictionary along with where along the route it was detected. Think of them like breadcrumbs
- Repeat this step for all signs along a specific route,
- Once all speed limit signs have been processed, join the speedlimit 'breadcrumbs' to create a series of lines. These lines represent the stretches of speed limit zones.
- After one side is processed, the reverse (inbound) side is processed in a similar way.
What types of signs are used to create speed limits?
What a great question. There are many different types of speed limit signs and we have attempted to capture them all as best as possible. Some of these signs are standard, US DOT signs (have a code starting with R2 or S5); others are customized local signage.
| Sign Code | Picture |
|---|---|
R2-1 |
|
R2-2 | |
R2-2P |
|
R2-4P |
|
R2-4a |
|
S5-1 |
|
R-NS-173 | |
R-NS-071 | |
W-NS-008 | |
R-NS-037 | |
R-NS-110 | |
R-NS-103 |
