Data
Every field in the record.
A mile of road with pylons on it makes a record with a fixed shape. This page is that shape: what is in it, how often, how exact, and what it answers.
01 / The register
What one mile makes, in numbers
8
Pylons to the mile
4
Sensors on each pylon
12
Measures
6
Object classes
5
Interval lengths, from 1 minute
40 ms
Tracker frame interval
5
Coverage states, and they sum to the window
0
Fields that hold a person
Each number above is set out in full below.
This page has no accuracy number. One accuracy number hides its own denominator: the count it was measured against. A thing that is never seen is never classed and never tracked, so one figure is standing in for three different things. Every number here carries that count. Every answer carries the coverage behind it.
02 / The record
The record, table by table
Every record is filed under a place and a window. Those two are the whole address. Nothing is filed under a thing that moved, so there is no third address for one to sit in.
A question and a stored row are different shapes. A question is made of where, when and why. That is the figure below. A stored row is found by a place and an interval start. A measure and a class then say what its number counts. That is the table under it. Neither shape has a slot for a who.
Fig 01
A query is made of
- WhereA geometryCeiling on area
- WhenA time windowCeiling on duration
- WhyA declared purposeRecorded, binding
There is no field for
- A name
- A plate
- A face
- A watchlist
- A standing alert
- A person, returning places
The record
| Field | Type | Unit | What it is |
|---|---|---|---|
| place | identifier | – | One spot on the road with a pylon bolted to a pole. It cannot move, so it cannot become a proxy for something that does. |
| place label | text | – | The place in words: an intersection, an approach, a block. |
| corridor | identifier | – | The run of instrumented road the place belongs to. The unit of coverage and of sale. |
| road authority | text | – | The agency in charge of the road, in plain words. |
| jurisdiction | text | – | The jurisdiction the place sits in. |
| mount | enum | pole, mast arm, gantry | The kind of structure the pylon sits on. |
| lanes | integer | lanes | Lanes at the place. |
| installed | date | – | The date the pylon went in. |
| window start | timestamp | ISO 8601, UTC | Start of the window. |
| window end | timestamp | ISO 8601, UTC | End of the window. Never a single instant. A place plus an instant points at one passage of one thing. |
| interval start | timestamp | ISO 8601, UTC | Start of a fixed-length interval. |
| interval length | enum | 1 minute, 5 minutes, 15 minutes, 1 hour, 1 day | The five lengths a question can use. |
| measure | enum, 12 values | – | Which of the twelve measures below. |
| class | enum, 6 values | vehicle, heavy vehicle, bus, bicycle, pedestrian, micromobility | What class of thing, in that moment. Never which thing. |
| value | number | per measure | The answer. |
| denominator | number | per measure | What the value is a share of. No answer ships without one. |
| precision | integer | decimal places | Fixed per measure, never whatever the math returned. |
| movement | enum | through, turning left, turning right, turning back | Which way it went through the place. |
| direction | enum | northbound, southbound, eastbound, westbound | Heading at the place. |
| speed band | enum | mph band | Which band the observed speed fell in. |
| time of day mask | enum | all hours, morning peak, midday, evening peak, overnight | Which hours of the window to include. |
| weather | enum | dry, wet, snow | What the pylon sensed at the roadside during the interval. |
That is the stored row. The fields below it narrow one moment. None of them describes a thing that lasts between passes.
The measures
| Measure | Unit | What it is a share of |
|---|---|---|
| volume | objects | objects through this place |
| turning movement | turns | objects through this place |
| speed distribution | mph at the 85th percentile | objects measured for speed |
| headway | seconds | following pairs observed |
| occupancy | percent of time occupied | seconds of detector time |
| queue length | objects at the stop line | cycles observed |
| gap acceptance | accepted gaps | gaps offered |
| mode split | percent of objects | objects through this place |
| conflict rate | conflicts | objects through this place |
| exposure denominator | objects | hours of observation |
| dwell | seconds | stops observed |
| sensed condition | hours in condition | hours of observation |
- Volume. Every object whose track crossed the place during the interval, counted once on exit. A track that spans two intervals lands in the one it left in, so nothing counts twice.
- Speed distribution. One speed stands for each track. We report the 85th percentile of those. We leave the mean out on purpose: a mean hides the tail that a design speed argument turns on.
- Exposure denominator. Objects through the place, over the hours the coverage record confirms. A safety rate is a count of harm divided by a count of exposure. The rate is only as checkable as that bottom number, so we publish that number on its own.
The pass record
| Field | Type | Unit | What it is |
|---|---|---|---|
| object number | identifier | – | Carried for the length of one pass. Retired on exit and never issued again. |
| class | enum, 6 values | – | The same six classes. |
| dimension signature | measurement | – | The size and shape signature of the thing that moved. |
| trajectory | path | position over time, world referenced | Whole across the junction, not restarted at the edge of each view. |
| speed along the path | number | mph | Speed taken at points along the track inside the place. |
| entry approach | enum | approach | The arm it entered on. |
| exit | enum | exit | The arm it left on. We drop a track that never resolves both ends rather than guess at it. |
| exit time | timestamp | ISO 8601, UTC | When it left. That timestamp is what puts the object in one interval and not two. |
| order of arrival | ordinal | – | The order things arrived in. |
| surrounding objects | list, same pass | – | Everything that was around it at the time. |
| tracker frame interval | interval | – | What the tracker means by continuity: this is the same shape it was 40 ms ago. It matches one shape to the next, and never learns whose. |
| handoff | adjacency | between two places | A handoff is one pylon passing an object to the next. The tracker carries the thread across it. All the record keeps is the adjacency: two fixed places that sit next to each other. |
Provenance and coverage
| Field | Type | Unit | What it is |
|---|---|---|---|
| pylon | identifier | RS-0142-A | Which pylon produced the record. |
| firmware | version | major.minor.patch | The firmware that produced it. |
| model version | text | – | The model that produced it. |
| calibrated on | date | – | When the sensors were last calibrated. |
| calibration due | date | – | When they are next due. |
| confidence | recorded value | – | Written at the same time as the rest of the provenance. |
| sensors and state | enum, per sensor | camera, lidar, radar, thermal, each nominal, degraded, failed or disabled | What the pylon could see when it made the record. A pylon that leaves a sensor out is a parse error. It never reads as healthy. |
| road authority | text | – | Which agency was in charge of the road, at the time. |
| notes in this window | text list | – | What happened at this place during this window, listed in full, never summed up. |
| observed | measurement | place hours | The pylon recorded normally. |
| degraded | measurement | place hours | The pylon recorded with a sensor or an overlap lost. Counts as half an hour. |
| dark | measurement | place hours | The pylon recorded nothing. |
| absent | measurement | place hours | No pylon stood at this place during the window. |
| expired | measurement | place hours | Older than the date the record at this place reaches back to. |
| coverage | percent | percent of the window | Observed hours plus half of degraded hours, over the hours in the window. |
| place hours | number | place hours | One place for one hour. |
| footprint state | enum | full, reduced, none | What the pylon can see now. |
| overlap | list of pylons | – | Which neighbors this pylon still overlaps. Overlap is the claim, and losing it is what a coverage gap is. |
| commissioned | date | – | A place can record before it is commissioned. An answer from before that date carries no warranty. |
Provenance is where a number came from. The pylon writes it with the record, never after. That is what makes an answer hold up a year later.
What is in it, and what is not
In the record
- place
- window
- class
- movement
- direction
- speed
- weather
- count
Not in the record
- plate string
- plate image crop
- face embedding
- face image crop
- any output of any recognition system
- name
- address
- vehicle registration
- vehicle identification number
- owner
- driver
- phone identifier, hardware address, or advertising id
- any object number carried across a pass
- any link between one pass and another
- any account, watchlist, or list of things a place can be matched against
- any standing alert on a subject
- any free text field on the data side
- any persistent attribute of a thing
- Tracker frame interval. 40 ms. That is what the tracker means by continuity: this is the same shape it was 40 ms ago.
- Coordinate frame. Measured against the world, not against a vehicle. That is what lets two pylons agree.
- Position. Shape and position at centimeter order, from lidar. Lidar measures distance with light.
- Timestamps. ISO 8601, in UTC, shown in one time zone your whole team shares. Everyone in one meeting reads the same number.
- Interval accounting. We count an object once, on exit, in the interval it left in. Intervals add up to the window and nothing counts twice.
The smaller the place, the longer the interval
| Place | Finest interval | Why |
|---|---|---|
| Corridor | 1 minute | A whole corridor in a minute is still a crowd. |
| Intersection | 5 minutes | A finer interval at one junction starts to show single passes. |
| Approach | 5 minutes | Same reason, one arm of the junction. |
| Block | 5 minutes | Same reason, one block between junctions. |
| One place | 15 minutes | The smallest place a question can name, so the longest floor. |
| One place, one direction | 15 minutes | A lane and a second is one vehicle wearing an aggregate's clothes: a number that reads as a crowd and is made of one. |
- The withholding floor is five. We hold back any cell that counts fewer than five objects. We hold back the next smallest cell in that row and column too, so subtraction cannot recover the first.
- The coverage floor is 80 percent. Under it an answer renders quieter. An export from under it carries a watermark that names the coverage behind it.
A pylon every quarter mile, and their footprints overlap. Where the sight lines are short we put them every eighth of a mile instead. More than one pylon sees an object at a time. The overlap is the claim, not decoration.
Every hour of a window lands in one of five states: observed, degraded, dark, absent, or expired. The five add up to the window, always. That is what makes the percentage checkable.
An observed hour counts as an hour. A degraded hour counts as half of one. A place whose pylon lost a sensor still answers, and answers less well. An hour with no record counts as nothing.
This is what the page prints in place of an accuracy number. Every answer arrives with the hours behind it, and the rule they were counted under.
Fig 02
05 / Questions
The questions this record answers
Every question below is answered from one place and one window. Today most of them take a survey, a consultant, or a person with a clicker.
| Role | The question | Answered from |
|---|---|---|
| City safety office | How many people were exposed at this corner, not just how many were hurt? | The exposure denominator, published as a number in its own right, not just as the bottom of a rate. Hard today: a crash report is the top of a rate with nothing under it. |
| City traffic engineer | Did the retiming cut the evening queue at this intersection, or move it to the next block? | Queue length and volume at two places, the same evening peak mask, two windows either side of the change. Hard today: a tube count at one place, once, for two days. |
| Transit planner | When the bus runs late, how many people are standing at this stop, and how long does it sit there? | Volume for the pedestrian class over the interval, plus dwell for the bus class. Hard today: the farebox counts who boarded. Nothing counts who was waiting. |
| Insurance adjuster | What was moving through this intersection at 14:32, how fast was it going, and what was around it? | The pass record for that place and window. Class, trajectory, speed along the path, order of arrival, surrounding objects, and the provenance of the pylon. The record does not say who drove. Hard today: two accounts that disagree and no third record. |
| Fleet safety manager | My driver says the cyclist came out of nowhere. What does the junction say? | The same pass record. The cyclist stays one cyclist while something blocks the view, instead of becoming a new object on the far side. Hard today: the dashcam looks out from inside the truck, and the truck is what was in the way. |
| Autonomy program | How many times did a vehicle brake here with nothing in front of it? What was in the junction our stack could not see? | Speed distribution and dwell over the window, plus the surrounding objects on each pass. Measured against the world, not against a vehicle. Hard today: the only witness to a phantom brake is the stack that did it. |
| Public works manager | Did the plow run this corridor, at plow speed, and how many times? | Volume and speed distribution for the heavy vehicle class, over the corridor and the storm window. Hard today: the contractor's own timesheet is the record. |
- Live. The pass record, streaming. For fleets and autonomy programs that read a corridor rather than ask it questions.
- The record. What was observed, with its provenance and its coverage. You ask by place and window. You take it away as CSV or JSON. Every export carries a manifest that names the question, the places, the window, the floor and the coverage.
- Imagery. A layer of a public street, which shows what a street shows. It is never a query result. You name a place and a window. Two named people approve it, and the request publishes.
Police and courts buy a place and a window on the same commercial terms as everyone else. There is no separate channel and no standing access.
Nothing here is on a public road yet.