Two grades for the road itself.
Torq turns the vertical vibration a phone feels in a mount into a ride comfort grade on the ISO 2631 scale and a roughness index on the IRI scale that road agencies use, then colors the route by it.
0.458 m/s² vertical RMS gives an ISO A; 3.0 m/km on a highway gives an IRI A.
The comfort scale
ISO 2631-1 relates frequency-weighted vertical acceleration to how a seated passenger feels.
| Grade | Vertical RMS, m/s² | ISO description |
|---|---|---|
| A+ | under 0.315 | not uncomfortable |
| A | 0.315 to 0.50 | a little uncomfortable |
| B | 0.50 to 0.80 | fairly uncomfortable |
| C | 0.80 to 1.25 | uncomfortable |
| D | 1.25 to 2.00 | very uncomfortable |
| F | over 2.00 | extremely uncomfortable |
The roughness scale
An IRI-style index in meters per kilometer, with two sets of thresholds because a city street is judged differently from a motorway.
| Highway, 50 km/h and up | IRI, m/km | Meaning |
|---|---|---|
| A | under 1.5 | smooth highway |
| B | 1.5 to 3.0 | good road |
| C | 3.0 to 4.5 | fair |
| D | 4.5 to 6.0 | poor |
| F | over 6.0 | very rough |
| Urban, under 50 km/h | IRI, m/km | Meaning |
|---|---|---|
| A | under 3.5 | good urban road |
| B | 3.5 to 5.5 | acceptable |
| C | 5.5 to 8.0 | fair, typical city |
| D | 8.0 to 12.0 | poor |
| F | over 12.0 | very rough |
How the vertical channel is measured
The accelerometer reports acceleration on the phone's three axes many times a second. Torq takes the axis aligned with gravity, removes gravity itself, and applies the frequency weighting from ISO 2631-1, which emphasizes the 4 to 8 Hz band where the human body is most sensitive to vertical vibration and de-emphasizes the rest. The root-mean-square of the weighted signal over the drive is the number both grades are built on.
Samples above 3 G are discarded as phone drops or mount slips. Stationary time is excluded, since a car idling at a light measures the engine, not the road. The barometer and the GPS altitude are used separately, for elevation gain and the elevation chart; they play no part in the roughness index.
Why the number is an estimate
A road agency measures IRI with a profiler that reads the pavement directly. A phone reads the pavement through tires, suspension, seat and mount, and each of those changes the answer: a sports car on hard tires will report a rougher road than a sedan on the same asphalt. Within one car the comparison is fair, and that is what the grade is for: this road against that one, this month's commute against last month's, the stretch that got repaved against the one that did not.
Where the grades appear
Both sit in the trip detail beside the driving score, with the vertical RMS and the roughness value shown under them. The replay map's Road color mode paints the route by roughness so the rough section is visible. And because the raw vertical channel is part of the sensor recording, the DPSE export carries it out of the app for anyone who wants to look closer.
Two ways to use it
The obvious one is curiosity: the road you have always thought was terrible now has a number. The useful one is comparison. Two routes to the same place, one smoother; a car before and after new tires or dampers; a road before and after the council resurfaced it. A grade you can repeat is a grade you can act on.
Questions people ask
How can a phone measure road quality?
Through the seat. The car's suspension turns the road profile into vertical acceleration in the cabin, and the phone's accelerometer measures that. Torq filters and frequency-weights the vertical channel as ISO 2631 specifies, computes its root-mean-square, and converts the result to a comfort grade and to a roughness index on the scale road agencies use.
What is IRI?
The International Roughness Index, in meters of vertical movement per kilometer of road, the standard way highway agencies rate pavement. A new motorway is around 1 m/km; a rough rural road is 5 or more. Torq estimates an IRI-style value from the phone's vibration. It is an estimate, because the car's suspension and tires sit between the road and the phone, but on the same car it is consistent from road to road.
What is the ride comfort grade?
The ISO 2631-1 scale, which maps frequency-weighted vertical RMS acceleration to how a passenger feels: A+ under 0.315 m/s² is not uncomfortable, A to 0.50 a little uncomfortable, B to 0.80 fairly uncomfortable, C to 1.25 uncomfortable, D to 2.00 very uncomfortable, F above that extremely uncomfortable.
Why do the road grades change with speed?
Because the same pavement feels different at 30 and at 100 km/h, and because urban roads have manhole covers and patches that would fail a highway threshold while being perfectly normal for a city street. Torq uses one set of IRI thresholds when the average speed is 50 km/h or more and a more forgiving set below that.
Does the phone need to be mounted for this?
Yes. Speed and route work with the phone anywhere, but the vertical channel measures whatever the phone is resting on. In a mount attached to the dashboard or a vent it measures the car; on a seat or in a pocket it measures the cushion or your leg. Torq also drops samples above 3 G as phone drops rather than road.
Is this grading my driving or the road?
Mostly the road and the car. A stiffly sprung car on a rough road will grade worse than a soft one on the same road regardless of who is driving. The grades sit beside the driving score rather than inside it for that reason; the score's efficiency and smoothness components are about you.
Can I see where a road was rough?
Yes. The replay map has a Road color mode that colors the route by roughness, so the bad stretch of a commute shows up as a red section you can scrub to.
A rough road, measured instead of remembered.
Mount the phone, drive the road, and read back a comfort grade on the ISO scale and a roughness index on the IRI scale.
iPhone, iOS 17 or later. No account. First drive free.