A summary of Urban SDK's Speed Limit Difference Data specification.
1.0 Introduction
Traffic speed data metrics are collected from vehicle navigation devices for every hour of day and quantify the speed that vehicles travel along a segment of road. The raw data is processed and compared with Speed Limit or Urban SDK Speed Category data to calculate the following metrics:
- Average Difference
- 50th Percentile Difference
- 85th Percentile Difference
- 95th Percentile Difference
⚠️NOTE: For customers who have integrated their speed limit data using Location Management settings, the Speed Difference layers will be calculated off of those integrated speed limits. For customers who have not integrated any speed limits, the layers will be calculated based on Urban SDK's Speed Category.
2.0 Methodology
Data Collection
Urban SDK gathers raw Traffic Speed data from vehicle navigation chips that are provided in 15-minute intervals. As vehicle navigation chips emit a location ping, it is tagged to the nearest road link over which the vehicle is travelling. This data is collected for every hour and every day throughout the year allowing a sample of trip speed observations to be collected on every public roadway within your community. This data is combined with either Urban SDK estimated speed limits, or customer uploaded Speed Limits to calculate the Speed Limit Difference data.
⚠️NOTE: On rare occasions where the number of trips travelling along a road is exceptionally low, the provided value will be null. These are typically in rural areas, and during times of the day where there is little to no traffic volume (i.e. if there are no trips to observe, there will be no speed observations to report).
Data Processing
The raw data collected by Urban SDK can be very large and difficult to work with for the purposes of traffic analysis. The amount of data collected in a major city for a single day would be too big to manage or analyze with conventional data analysis tools like Excel or Access, never mind trying to analyze an entire year's worth of data! For this reason, Urban SDK aggregates the data to hourly intervals and processes Traffic Speed metrics in a format that can easily be queried, analyzed, and downloaded without requiring any complex database storage on your network.
- Average Difference: Quantifies the difference between the speed limit and average speed of observed trips along a road segment. It is provided in miles per hour (mph).
- 50th Percentile Difference: Quantifies the difference between the speed limit and the speed at or below which 50% of observed trips travel along a road segment. It is provided in miles per hour (mph).
- 85th Percentile Difference: Quantifies the difference between the speed limit and the speed at or below which 85% of observed trips travel along a road segment. It is provided in miles per hour (mph).
- 95th Percentile Difference: Quantifies the difference between the speed limit and the speed at or below which 95% of observed trips travel along a road segment. It is provided in miles per hour (mph).
- Speed Limit: Represents Urban SDK Speed Limits unless custom speed limits have been integrated, which then take precedence. The Urban SDK Speed Limit provides an estimate of what a reasonable speed limit would be on a road, within +/- 5mph. It is provided in miles per hour (mph).
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- How Urban SDK Speed Limit is Calculated: Urban SDK Speed Limit is a model which provides a best estimate of posted speed limits on road links for which no ground truth speed limit is available. We use a combination of the road functional class, speed category information provided by the raw data provider, and off-peak observed average travel speeds to estimate Urban SDK Speed Limit. As we continue to receive ground truth speed limit data from our customers within their boundaries, we are refining and updating Urban SDK Speed Limit to improve our level of accuracy in estimating posted speed limits with this metric.
⚠️NOTE: For customers with integrated speed limit data: If not all streets are updated, the difference layers will use available speed limits, or the Urban SDK Speed Limit as needed.
3.0 Data Specification
Metadata Fields
Metadata fields that are provided for all data are detailed in Urban SDK's Linear Referencing System (LRS) specification.
Data Fields
The following table is the format in which downloaded Traffic Speed data will be provided:
| Field | Type | Description |
|
|
integer | The year associated with the provided data. |
|
|
integer | The month associated with the provided data as an integer between 1 and 12. |
|
|
integer |
The period of day associated with the provided data as an integer between 1 and 7:
|
|
|
integer |
The hour of day associated with the provided data as an integer between 1 and 24. |
|
|
string |
Identifies which data is provided:
|
|
|
integer |
Urban SDK Speed Limits unless custom speed limits have been integrated, which then take precedence. |
|
|
numeric |
The calculated value for Mondays within the selected period. |
|
|
numeric |
The calculated value for Tuesdays within the selected period. |
|
|
numeric |
The calculated value for Wednesdays within the selected period. |
|
|
numeric |
The calculated value for Thursdays within the selected period. |
|
|
numeric |
The calculated value for Fridays within the selected period. |
|
|
numeric |
The calculated value for Saturdays within the selected period. |
|
|
numeric |
The calculated value for Sundays within the selected period. |
|
|
numeric |
The calculated value for Weekdays within the selected period. |
|
|
numeric |
The calculated value for Weekend days within the selected period. |
|
|
numeric |
The calculated value for a typical week within the selected period. |
Urban SDK Value: For convenience, data is disaggregated by Month, Period of Day, Hour of Day, by Day of Week, Weekday/Weekends, as well as Weekly values to make it easy for customers to see and compare the differences in Traffic Speed at a scale suitable for each customer's unique analysis needs.