How it works

The app credits Interstate completion, not distance travelled. It does not meter your pavement; it works out which stretches of which routes you have finished.

What gets counted

One exit to the next is the unit. Drive that stretch and it is clinched — credited in full, whatever path you took through the ramps at either end. Small gaps inside an interchange count as connected.

Stretches are measured in reference miles: the milepost value of each junction, in tenths, the same ruler the road signs its own mileposts by. So the miles you have driven and the miles a route has are measured the same way.

Driving the same stretch twice credits it once. The second pass is history, not new road.

Five figures on the dashboard come out of that:

• Interstate miles — reference miles you have clinched, exit to exit.
• System % — that figure as a share of the whole network.
• Routes driven — routes with any credit at all.
• Routes complete — routes at 100%.
• States touched — states with any credit.

Red and green

Red is the mile you drove. Green is the route you finished. That is the printed atlas convention, and it holds on the phone, in the browser and in an export.

How a mile was earned is always visible as a shape, never as a color alone:

• GPS-verified — a solid line. A drive you recorded, or a GPX file you imported.
• Manual claim — the same red, dashed. Road you drove before the app existed and entered by hand.
• Bridged — a stretch the app closed over a gap in the trace, because the travel on both sides showed the drive continued.
• Not driven — a thin grey line.

All three kinds of credit count toward the figures above. The map’s filter changes the map only.

Why some numbers carry ≈

A junction whose reference mile is anchored — to a state milepost layer, the National Bridge Inventory, or signed exit numbers — gives an exact figure. Where nothing anchors it, the app measures along the road’s own geometry instead and marks the figure ≈, captioned “route measure”. A position between two junctions reads as an APPROX. MILE MARKER, and it can sit half a mile from the sign you pass.

The distinction is the point: a number with no ≈ is the milepost system’s, and a number with one is the map’s.

From your trace to coverage

Recording. While a trip runs, the app samples your position. Nothing is matched yet. What it holds is a trace: positions and times.

Matching. When the trip ends, the trace is compared with the Interstate centerlines that ship inside the app, on the phone. The matcher decides which stretches of which routes you drove, and where along each route you got on and off.

Frontage roads run beside an Interstate for miles, often within GPS error of the highway. Ramps and parallel surface streets produce traces that look right too. The matcher spends most of its effort ruling those out, because crediting a road you didn’t drive is the one mistake you would notice. It does not always win — known limitations has the case that beat it.

Coverage. Clinched stretches add up per route, per state and across the system. The same derivation runs again on the server once a trip is uploaded, so a better matcher or a better map can re-read an old drive and credit it properly.

Why your total may differ from the official one

The FHWA publishes an official length for each route. The app measures each route from the geometry it matches against, and the two are rarely identical: they are measured differently, and the source data has its own vintage.

Where they disagree, the app’s percentages use its own measurement. A route’s miles and your miles on it always come from the same ruler.

Where the map comes from

The Interstate geometry is built from Census TIGER/Line primary roads, filtered to Interstate routes, with divided highways averaged into one centerline — so driving one direction fills in the whole road.

Route facts come from the FHWA route log: official lengths, which states a route runs through, where it begins and ends. State boundaries come from the Census cartographic boundary files.

Exit locations come from OpenStreetMap (© OpenStreetMap contributors, ODbL). An exit here is a point on the centerline where a numbered interchange leaves the road — the boundary between two stretches of credit, so the app carries the location and the number rather than the ramps.

The federal sources are public domain and OpenStreetMap’s license permits redistribution with credit, which is why the whole network can be bundled with the app, and why matching works with no signal. What that network holds, counted: