diff --git a/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidator.java b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidator.java
new file mode 100644
index 0000000000..363f3c385e
--- /dev/null
+++ b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidator.java
@@ -0,0 +1,109 @@
+package org.mobilitydata.gtfsvalidator.validator;
+
+import java.util.List;
+import java.util.Optional;
+import javax.inject.Inject;
+import org.mobilitydata.gtfsvalidator.annotation.GtfsValidator;
+import org.mobilitydata.gtfsvalidator.notice.MissingRequiredFieldNotice;
+import org.mobilitydata.gtfsvalidator.notice.NoticeContainer;
+import org.mobilitydata.gtfsvalidator.table.GtfsContinuousPickupDropOff;
+import org.mobilitydata.gtfsvalidator.table.GtfsRoute;
+import org.mobilitydata.gtfsvalidator.table.GtfsRouteTableContainer;
+import org.mobilitydata.gtfsvalidator.table.GtfsStopTime;
+import org.mobilitydata.gtfsvalidator.table.GtfsStopTimeTableContainer;
+import org.mobilitydata.gtfsvalidator.table.GtfsTrip;
+import org.mobilitydata.gtfsvalidator.table.GtfsTripTableContainer;
+
+/**
+ * Validates that {@code trips.shape_id} is defined when the trip has continuous pickup or drop-off
+ * behavior.
+ *
+ * <p>The spec makes {@code trips.shape_id} conditionally required: it is required if the trip has a
+ * continuous pickup or drop-off behavior defined either in {@code routes.txt} or in {@code
+ * stop_times.txt}, and optional otherwise.
+ *
+ * <p>A value of {@code 1}, like an empty value, means no continuous stopping behavior, so only
+ * {@code 0}, {@code 2} and {@code 3} make {@code shape_id} required. Values in {@code
+ * stop_times.txt} override those in {@code routes.txt}.
+ *
+ * <p>Generated notice: {@link MissingRequiredFieldNotice}.
+ */
+@GtfsValidator
+public class TripShapeIdConditionalValidator extends FileValidator {
+  private final GtfsRouteTableContainer routeTable;
+  private final GtfsTripTableContainer tripTable;
+  private final GtfsStopTimeTableContainer stopTimeTable;
+
+  @Inject
+  TripShapeIdConditionalValidator(
+      GtfsRouteTableContainer routeTable,
+      GtfsTripTableContainer tripTable,
+      GtfsStopTimeTableContainer stopTimeTable) {
+    this.routeTable = routeTable;
+    this.tripTable = tripTable;
+    this.stopTimeTable = stopTimeTable;
+  }
+
+  @Override
+  public void validate(NoticeContainer noticeContainer) {
+    for (GtfsTrip trip : tripTable.getEntities()) {
+      if (trip.hasShapeId()) {
+        continue;
+      }
+      if (hasContinuousBehavior(trip)) {
+        noticeContainer.addValidationNotice(
+            new MissingRequiredFieldNotice(
+                GtfsTrip.FILENAME, trip.csvRowNumber(), GtfsTrip.SHAPE_ID_FIELD_NAME));
+      }
+    }
+  }
+
+  /**
+   * Returns true if any stop time of this trip has continuous pickup or drop-off behavior, falling
+   * back to the values on the route where the stop time does not set them.
+   */
+  private boolean hasContinuousBehavior(GtfsTrip trip) {
+    Optional<GtfsRoute> route = routeTable.byRouteId(trip.routeId());
+    GtfsContinuousPickupDropOff routePickup =
+        route.map(GtfsRoute::continuousPickup).orElse(GtfsContinuousPickupDropOff.NOT_AVAILABLE);
+    GtfsContinuousPickupDropOff routeDropOff =
+        route.map(GtfsRoute::continuousDropOff).orElse(GtfsContinuousPickupDropOff.NOT_AVAILABLE);
+
+    List<GtfsStopTime> stopTimes = stopTimeTable.byTripId(trip.tripId());
+    if (stopTimes.isEmpty()) {
+      return isContinuous(routePickup) || isContinuous(routeDropOff);
+    }
+    for (GtfsStopTime stopTime : stopTimes) {
+      GtfsContinuousPickupDropOff pickup =
+          stopTime.hasContinuousPickup() ? stopTime.continuousPickup() : routePickup;
+      GtfsContinuousPickupDropOff dropOff =
+          stopTime.hasContinuousDropOff() ? stopTime.continuousDropOff() : routeDropOff;
+      if (isContinuous(pickup) || isContinuous(dropOff)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  private static boolean isContinuous(GtfsContinuousPickupDropOff value) {
+    return value == GtfsContinuousPickupDropOff.ALLOWED
+        || value == GtfsContinuousPickupDropOff.MUST_PHONE
+        || value == GtfsContinuousPickupDropOff.ON_REQUEST_TO_DRIVER;
+  }
+
+  @Override
+  public boolean shouldCallValidate() {
+    if (tripTable == null) {
+      return false;
+    }
+    boolean routeDefinesContinuous =
+        routeTable != null
+            && (routeTable.hasColumn(GtfsRoute.CONTINUOUS_PICKUP_FIELD_NAME)
+                || routeTable.hasColumn(GtfsRoute.CONTINUOUS_DROP_OFF_FIELD_NAME));
+    boolean stopTimeDefinesContinuous =
+        stopTimeTable != null
+            && (stopTimeTable.hasColumn(GtfsStopTime.CONTINUOUS_PICKUP_FIELD_NAME)
+                || stopTimeTable.hasColumn(GtfsStopTime.CONTINUOUS_DROP_OFF_FIELD_NAME));
+    return routeDefinesContinuous || stopTimeDefinesContinuous;
+  }
+}
diff --git a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidatorTest.java b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidatorTest.java
new file mode 100644
index 0000000000..09e897c5f9
--- /dev/null
+++ b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/TripShapeIdConditionalValidatorTest.java
@@ -0,0 +1,143 @@
+package org.mobilitydata.gtfsvalidator.validator;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mobilitydata.gtfsvalidator.notice.MissingRequiredFieldNotice;
+import org.mobilitydata.gtfsvalidator.notice.NoticeContainer;
+import org.mobilitydata.gtfsvalidator.notice.ValidationNotice;
+import org.mobilitydata.gtfsvalidator.table.GtfsRoute;
+import org.mobilitydata.gtfsvalidator.table.GtfsRouteTableContainer;
+import org.mobilitydata.gtfsvalidator.table.GtfsStopTime;
+import org.mobilitydata.gtfsvalidator.table.GtfsStopTimeTableContainer;
+import org.mobilitydata.gtfsvalidator.table.GtfsTrip;
+import org.mobilitydata.gtfsvalidator.table.GtfsTripTableContainer;
+
+@RunWith(JUnit4.class)
+public class TripShapeIdConditionalValidatorTest {
+
+  private static List<ValidationNotice> generateNotices(
+      List<GtfsRoute> routes, List<GtfsTrip> trips, List<GtfsStopTime> stopTimes) {
+    NoticeContainer noticeContainer = new NoticeContainer();
+    new TripShapeIdConditionalValidator(
+            GtfsRouteTableContainer.forEntities(routes, noticeContainer),
+            GtfsTripTableContainer.forEntities(trips, noticeContainer),
+            GtfsStopTimeTableContainer.forEntities(stopTimes, noticeContainer))
+        .validate(noticeContainer);
+    return noticeContainer.getValidationNotices();
+  }
+
+  private static GtfsRoute.Builder route() {
+    return new GtfsRoute.Builder().setCsvRowNumber(2).setRouteId("route1");
+  }
+
+  private static GtfsTrip.Builder trip() {
+    return new GtfsTrip.Builder().setCsvRowNumber(3).setTripId("trip1").setRouteId("route1");
+  }
+
+  private static GtfsStopTime.Builder stopTime(int csvRowNumber) {
+    return new GtfsStopTime.Builder()
+        .setCsvRowNumber(csvRowNumber)
+        .setTripId("trip1")
+        .setStopSequence(csvRowNumber);
+  }
+
+  private static MissingRequiredFieldNotice expectedNotice() {
+    return new MissingRequiredFieldNotice("trips.txt", 3, "shape_id");
+  }
+
+  @Test
+  public void continuousPickupOnRouteWithoutShapeIdShouldGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(0).build()),
+            List.of(trip().build()),
+            List.of(stopTime(4).build()));
+    assertThat(notices).containsExactly(expectedNotice());
+  }
+
+  @Test
+  public void continuousDropOffOnRouteWithoutShapeIdShouldGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousDropOff(2).build()),
+            List.of(trip().build()),
+            List.of(stopTime(4).build()));
+    assertThat(notices).containsExactly(expectedNotice());
+  }
+
+  @Test
+  public void continuousPickupOnStopTimeWithoutShapeIdShouldGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().build()),
+            List.of(trip().build()),
+            List.of(stopTime(4).build(), stopTime(5).setContinuousPickup(3).build()));
+    assertThat(notices).containsExactly(expectedNotice());
+  }
+
+  @Test
+  public void continuousBehaviorWithShapeIdShouldNotGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(0).build()),
+            List.of(trip().setShapeId("shape1").build()),
+            List.of(stopTime(4).build()));
+    assertThat(notices).isEmpty();
+  }
+
+  @Test
+  public void notAvailableContinuousBehaviorShouldNotGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(1).setContinuousDropOff(1).build()),
+            List.of(trip().build()),
+            List.of(stopTime(4).setContinuousPickup(1).setContinuousDropOff(1).build()));
+    assertThat(notices).isEmpty();
+  }
+
+  @Test
+  public void stopTimeShouldOverrideContinuousBehaviorOnRoute() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(0).build()),
+            List.of(trip().build()),
+            List.of(stopTime(4).setContinuousPickup(1).build()));
+    assertThat(notices).isEmpty();
+  }
+
+  @Test
+  public void oneOverridingStopTimeWithContinuousBehaviorShouldGenerateNotice() {
+    // Every stop time overrides the route, but one of them overrides it to a continuous value, so
+    // the trip still needs a shape.
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(0).build()),
+            List.of(trip().build()),
+            List.of(
+                stopTime(4).setContinuousPickup(1).build(),
+                stopTime(5).setContinuousPickup(1).build(),
+                stopTime(6).setContinuousPickup(2).build(),
+                stopTime(7).setContinuousPickup(1).build()));
+    assertThat(notices).containsExactly(expectedNotice());
+  }
+
+  @Test
+  public void noContinuousBehaviorShouldNotGenerateNotice() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().build()), List.of(trip().build()), List.of(stopTime(4).build()));
+    assertThat(notices).isEmpty();
+  }
+
+  @Test
+  public void tripWithoutStopTimesShouldStillUseRouteContinuousBehavior() {
+    List<ValidationNotice> notices =
+        generateNotices(
+            List.of(route().setContinuousPickup(2).build()), List.of(trip().build()), List.of());
+    assertThat(notices).containsExactly(expectedNotice());
+  }
+}