What Twistly measures

Every mapping app in the world answers the same question: what is the quickest way from here to there. That is a good question, and it is not the one you are asking on a Sunday morning. Nothing routes for the drive itself — for the road that is worth the extra forty minutes.

Asking a chatbot instead gets you confident, invented geography: a road that does not connect, a pass that has been closed since 2019, a village on the wrong side of a river. Twistly is built so that cannot happen. The language model reads what you asked for and chooses between roads it was handed; it never draws geometry and never names a road that was not returned by a query against real data.

That distinction is the whole product, and it was learned the hard way. Rank roads by curviness alone and the top of the list fills with residential streets — the curviest class of road on any map, and the worst drive on it. A cul-de-sac with four ninety-degree bends in three hundred metres scores brilliantly and gives you nothing. Length is what turns a shape into a drive.

The numbers are smaller than you would guess. A synthetic test arc reaches 0.9. The best A-road in Derbyshire reaches 0.28. Anyone who tunes a road scorer against made-up geometry is wrong by a factor of three, which is why every threshold in Twistly is set against real roads.

Every road in Great Britain is measured once, in a monthly pass over the OpenStreetMap extract, and stored with more than its shape:

• How much genuine curve it gives, and over what distance.

• Its speed limit, its surface and how wide it is.

• How built-up its surroundings are — the difference between a lane and a bypass.

• How close it runs to water, coast, forest and open moor.

• Where the speed cameras on it sit.

• How much traffic it typically carries, from the Department for Transport’s roadside counts.

• What it runs past — the towns, villages and landmarks along its length.

Those are features, not opinions. When a route brief calls a road coastal, there is a measured share of coastline behind the word, and when there is not, the word does not get used.

Choosing the roads is ours. Connecting them is not. Twistly selects the roads a drive is built around by querying its own scored database — its curvature, its urban score, its enrichment. A routing engine then joins those roads into something legally drivable, and it is our own engine on our own server, not a third party’s.

Then the finished route is measured again, with the same metric, including every connecting road the router chose for itself. That second measurement is the one you see. A route is accepted on our numbers or not at all — which also means a route that doubles back on itself scores worse for it, rather than counting the good road’s corners twice.

You get three routes to compare, and they are three different decisions rather than one drive described three ways. Where the geography allows, they are a ladder of increasing detour, offered shortest first. Where it does not, they differ in what they emphasise. If only two genuinely different drives exist, you get two.

The headline metric is curvy share, measured on the finished route. Every other number on a route page has its definition available next to it, because three similar percentages on one screen — one of them mislabelled — is how a metric stops meaning anything.

If a route comes back at 84 km when you asked for 100, it says so rather than showing a green tick. On target means within ten per cent of what you asked for, in the unit you asked in: a request in hours is judged on time, not on distance.

• No timings. No leaderboards, no road records, no fastest-anything, in the product, the API or the copy. If you log a drive it is yours and it stays private. This is not a feature we have not got round to; it is a line.

• No encouragement to hurry. Route names, briefs and descriptions never suggest driving faster than is legal or sensible, and every route carries the note to drive to the conditions and obey the limits.

• No invented geography. The model may only refer to roads and places a query actually returned. Anything else fails the request rather than reaching you.

• OpenStreetMap. Every road, junction and place on Twistly comes from OpenStreetMap, under the Open Database Licence. Source.

• Department for Transport road traffic counts. How much traffic a road typically carries, from the DfT’s roadside counts. Source.

• Wikimedia Commons. The photographs on road pages, each shown with its author and licence, and captioned as near the road rather than of it. Source.

Map data © OpenStreetMap contributors, under the Open Database Licence. Twistly’s scored road database is derived from it and stays on our own servers; the routes generated from it are produced works, and yours to use.

Twistly is in beta, and it is British: every road in Great Britain is scored, and nothing beyond it is. Route quality is the genuinely hard part of this product and it is where the work goes.

If a route comes back wrong, tell us — the feedback page exists for exactly that, and a bad route with the prompt that produced it is the most useful thing anyone can send. Anything else, write to hello@twistly.co.uk.