diff --git a/backend/README.md b/backend/README.md
index 2711bffcd..ec70ffaac 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -30,6 +30,7 @@ Names and regions should match above.
 1.  `gcloud storage --project=$PROJECT buckets create gs://$PROJECT --location=EUROPE-WEST2 --uniform-bucket-level-access`
 2.  Generate fake scheme data and upload it: `npm run generate-random-schemes && gsutil cp random_schemes.geojson gs://$PROJECT/`
 3.  Sync current public layers to GCS. This only works if you have S3 access (aka Dustin). Skip these otherwise, or download another way. This might take a few minutes, depending on your connection: `aws s3 sync s3://atip.uk/layers layers; gsutil -m cp -r ./layers gs://$PROJECT/`
+4.  Also copy private files (currently [only from Ordnance Survey](https://github.com/acteng/atip-data-prep/tree/main/ordnance_survey_layers)) into `gs://$PROJECT/private_layers/v1/`. These have to be generated by a developer; they can't be mirrored from S3, because our S3 bucket is only appropriate for public data.
 
 ### Deploy
 
diff --git a/src/lib/browse/LayerControls.svelte b/src/lib/browse/LayerControls.svelte
index 566b04777..9c6a790fa 100644
--- a/src/lib/browse/LayerControls.svelte
+++ b/src/lib/browse/LayerControls.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
   import {
+    appVersion,
     BaselayerSwitcher,
     CollapsibleCard,
     StreetViewController,
@@ -21,6 +22,8 @@
   import ParliamentaryConstituenciesLayerControl from "./layers/ParliamentaryConstituenciesLayerControl.svelte";
   import PctLayerControl from "./layers/PctLayerControl.svelte";
   import RailwayStationsLayerControl from "./layers/RailwayStationsLayerControl.svelte";
+  import RoadSpeedsLayerControl from "./layers/RoadSpeedsLayerControl.svelte";
+  import RoadWidthsLayerControl from "./layers/RoadWidthsLayerControl.svelte";
   import SchoolsLayerControl from "./layers/SchoolsLayerControl.svelte";
   import SportsSpacesLayerControl from "./layers/SportsSpacesLayerControl.svelte";
   import VehicleCountsLayerControl from "./layers/VehicleCountsLayerControl.svelte";
@@ -73,6 +76,10 @@
   <CollapsibleCard label="Other">
     <VehicleCountsLayerControl />
     <PctLayerControl />
+    {#if appVersion() == "Private (development)"}
+      <RoadWidthsLayerControl />
+      <RoadSpeedsLayerControl />
+    {/if}
   </CollapsibleCard>
   <StreetViewController
     bind:this={streetViewController}
diff --git a/src/lib/browse/layers/RoadSpeedsLayerControl.svelte b/src/lib/browse/layers/RoadSpeedsLayerControl.svelte
new file mode 100644
index 000000000..93f1173f5
--- /dev/null
+++ b/src/lib/browse/layers/RoadSpeedsLayerControl.svelte
@@ -0,0 +1,110 @@
+<script lang="ts">
+  import { ExternalLink, HelpButton, InteractiveLayer } from "lib/common";
+  import { Checkbox, Radio } from "lib/govuk";
+  import {
+    hoveredToggle,
+    makeColorRamp,
+    overwriteLineLayer,
+    overwritePmtilesSource,
+  } from "lib/maplibre";
+  import type { MapGeoJSONFeature } from "maplibre-gl";
+  import { map } from "stores";
+  import { colors, denseLineWidth } from "../colors";
+  import SequentialLegend from "./SequentialLegend.svelte";
+
+  let name = "road_speeds";
+  let colorScale = colors.sequential_low_to_high;
+  let limits = [0, 20, 30, 40, 50, 90];
+
+  let showSpeed = "indicative_mph";
+
+  overwritePmtilesSource(
+    $map,
+    name,
+    `${import.meta.env.VITE_RESOURCE_BASE}/private_layers/v1/${name}.pmtiles`
+  );
+
+  overwriteLineLayer($map, {
+    id: name,
+    source: name,
+    sourceLayer: name,
+    color: makeColorRamp(["get", showSpeed], limits, colorScale),
+    width: denseLineWidth,
+    opacity: hoveredToggle(0.5, 1.0),
+  });
+
+  let show = false;
+
+  function tooltip(feature: MapGeoJSONFeature): string {
+    // @ts-ignore Trusting the input data has the correct form
+    let time = {
+      mf4to7: "Monday-Friday 4-7am",
+      mf7to9: "Monday-Friday 7-9am",
+      mf9to12: "Monday-Friday 9am-12pm",
+      mf12to14: "Monday-Friday 12-2pm",
+      mf14to16: "Monday-Friday 2-4pm",
+      mf16to19: "Monday-Friday 4-7pm",
+      mf19to22: "Monday-Friday 7-10pm",
+      mf22to4: "Monday-Friday 10pm-4am",
+      ss4to7: "Saturday-Sunday 4-7am",
+      ss7to10: "Saturday-Sunday 7-10am",
+      ss10to14: "Saturday-Sunday 10am-2pm",
+      ss14to19: "Saturday-Sunday 2-7pm",
+      ss19to22: "Saturday-Sunday 7-10pm",
+      ss22to4: "Saturday-Sunday 10pm-4am",
+    }[feature.properties.highest_description];
+    let x = `<p>Posted speed limit: ${feature.properties.indicative_mph} mph</p>`;
+    x += `<p>Highest average speed: ${feature.properties.highest_mph} mph (during ${time})</p>`;
+    return x;
+  }
+
+  function changeStyle() {
+    $map.setPaintProperty(
+      name,
+      "line-color",
+      makeColorRamp(["get", showSpeed], limits, colorScale)
+    );
+  }
+</script>
+
+<Checkbox id={name} bind:checked={show}>
+  OS Speeds
+  <span slot="right">
+    <HelpButton>
+      <p>
+        The average speed data is collected over a six-month period by <ExternalLink
+          href="https://basemap.co.uk/speed-data"
+        >
+          Basemap
+        </ExternalLink> from 135,000 vehicle telematic systems and provided through
+        Ordnance Survey. The averages are grouped by different time periods for weekdays
+        and weekends. This map shows the highest average.
+      </p>
+      <p>Data valid as of 1 September, 2023</p>
+      <p>
+        License: Contains OS data &copy; Crown copyright and database right
+        2023. Made available under the <ExternalLink
+          href="https://www.ordnancesurvey.co.uk/documents/licensing/psga-member-licence.pdf"
+        >
+          Public Sector Geospatial Agreement
+        </ExternalLink>.
+      </p>
+    </HelpButton>
+  </span>
+</Checkbox>
+{#if show}
+  <SequentialLegend {colorScale} {limits} />
+  <Radio
+    legend="Show speed types"
+    id="showSpeed"
+    choices={[
+      ["indicative_mph", "Posted speed limit"],
+      ["highest_mph", "Highest measured average speed"],
+    ]}
+    bind:value={showSpeed}
+    on:change={changeStyle}
+    inlineSmall
+  />
+{/if}
+
+<InteractiveLayer layer={name} {tooltip} {show} clickable={false} />
diff --git a/src/lib/browse/layers/RoadWidthsLayerControl.svelte b/src/lib/browse/layers/RoadWidthsLayerControl.svelte
new file mode 100644
index 000000000..8901c7809
--- /dev/null
+++ b/src/lib/browse/layers/RoadWidthsLayerControl.svelte
@@ -0,0 +1,70 @@
+<script lang="ts">
+  import { ExternalLink, HelpButton, InteractiveLayer } from "lib/common";
+  import { Checkbox } from "lib/govuk";
+  import {
+    hoveredToggle,
+    makeColorRamp,
+    overwriteLineLayer,
+    overwritePmtilesSource,
+  } from "lib/maplibre";
+  import type { MapGeoJSONFeature } from "maplibre-gl";
+  import { map } from "stores";
+  import { colors, denseLineWidth } from "../colors";
+  import SequentialLegend from "./SequentialLegend.svelte";
+
+  let name = "road_widths";
+  let colorScale = colors.sequential_low_to_high;
+  let limits = [0, 5, 10, 15, 20, 100];
+
+  overwritePmtilesSource(
+    $map,
+    name,
+    `${import.meta.env.VITE_RESOURCE_BASE}/private_layers/v1/${name}.pmtiles`
+  );
+
+  overwriteLineLayer($map, {
+    id: name,
+    source: name,
+    sourceLayer: name,
+    color: makeColorRamp(["get", "average"], limits, colorScale),
+    // TODO Try showing the actual width, in meters and not pixels
+    width: denseLineWidth,
+    opacity: hoveredToggle(0.5, 1.0),
+  });
+
+  let show = false;
+
+  function tooltip(feature: MapGeoJSONFeature): string {
+    let x = `<p>Average width: ${feature.properties.average} meters</p>`;
+    x += `<p>Minimum width: ${feature.properties.minimum} meters</p>`;
+    return x;
+  }
+</script>
+
+<Checkbox id={name} bind:checked={show}>
+  OS Road widths
+  <span slot="right">
+    <HelpButton>
+      <p>
+        This is average and minimum road carriageway width (in meters) from
+        Ordnance Survey. The coloring shows the average width, and the line
+        thickness has no meaning. Be careful interpreting the data near dual
+        carriageways and crossing islands.
+      </p>
+      <p>Data valid as of 1 September, 2023</p>
+      <p>
+        License: Contains OS data &copy; Crown copyright and database right
+        2023. Made available under the <ExternalLink
+          href="https://www.ordnancesurvey.co.uk/documents/licensing/psga-member-licence.pdf"
+        >
+          Public Sector Geospatial Agreement
+        </ExternalLink>.
+      </p>
+    </HelpButton>
+  </span>
+</Checkbox>
+{#if show}
+  <SequentialLegend {colorScale} {limits} />
+{/if}
+
+<InteractiveLayer layer={name} {tooltip} {show} clickable={false} />
diff --git a/src/lib/maplibre/utils.ts b/src/lib/maplibre/utils.ts
index 6c04045b1..b7b94a9d3 100644
--- a/src/lib/maplibre/utils.ts
+++ b/src/lib/maplibre/utils.ts
@@ -324,6 +324,8 @@ const layerZorder = [
   "vehicle_counts",
   "pct_commute",
   "pct_school",
+  "road_widths",
+  "road_speeds",
 
   // Polygons are bigger than lines, which're bigger than points. When geometry
   // overlaps, put the smaller thing on top