diff --git a/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php b/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php
index 5781b23..bbd2898 100644
--- a/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php
+++ b/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php
@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace App\Form\Service;
 
 use App\BusProNet\Constants;
+use App\BusProNet\Model\Service;
 use App\BusProNet\Utility\DirectionMapper;
 use App\Form\Model\BookingDto;
 use App\Form\Service\Abstract\AbstractParticipantFieldHandler;
@@ -122,6 +123,8 @@ class ParticipantTransportationDiscountReplacementFieldHandler extends AbstractP
                         $regularPkw->label
                     )
                 );
+
+                $this->syncBookingTransportationService($bookingDto, $participantIndex, $discountedPkw, $regularPkw);
             }
 
             return; // Done processing for BUS inbound scenario
@@ -168,6 +171,46 @@ class ParticipantTransportationDiscountReplacementFieldHandler extends AbstractP
                     $discountedPkw->label
                 )
             );
+
+            $this->syncBookingTransportationService($bookingDto, $participantIndex, $regularPkw, $discountedPkw);
+        }
+    }
+
+    /**
+     * Keeps $bookingDto->booking->transportationServices consistent with a participant's
+     * updated outbound transportation selection. Only runs in edit mode.
+     *
+     * Clones the new service before inserting it to avoid mutating the shared travel-data
+     * object when resetServiceMappings() clears mappings at submit time.
+     */
+    private function syncBookingTransportationService(
+        BookingDto $bookingDto,
+        int $participantIndex,
+        Service $oldService,
+        Service $newService,
+    ): void {
+        if (null === $bookingDto->booking) {
+            return;
+        }
+
+        $services = &$bookingDto->booking->transportationServices;
+
+        if (isset($services[$oldService->id])) {
+            $services[$oldService->id]->mapping = array_values(
+                array_filter(
+                    $services[$oldService->id]->mapping,
+                    fn(int $idx): bool => $idx !== $participantIndex,
+                )
+            );
+        }
+
+        if (false === isset($services[$newService->id])) {
+            $services[$newService->id] = clone $newService;
+            $services[$newService->id]->mapping = [];
+        }
+
+        if (false === in_array($participantIndex, $services[$newService->id]->mapping, true)) {
+            $services[$newService->id]->mapping[] = $participantIndex;
         }
     }
 }