diff --git a/config/services.yaml b/config/services.yaml
index a5e2400..b5f933c 100644
--- a/config/services.yaml
+++ b/config/services.yaml
@@ -71,6 +71,7 @@ services:
     # Insurance Field Handlers with dependencies
     App\Form\Service\ParticipantInsuranceFieldHandler: ~
     App\Form\Service\ParticipantBulkInsuranceFieldHandler: ~
+    App\Form\Service\ParticipantTransportationDiscountReplacementFieldHandler: ~
 
     # Participant Field Handler Registry - most handlers instantiate dependencies directly, some use services
     App\Form\Service\ParticipantFieldHandlerRegistry:
@@ -92,5 +93,6 @@ services:
                 - 'App\Form\Service\ParticipantRentalInsuranceFieldHandler'
                 - 'App\Form\Service\ParticipantLicensePlateFieldHandler'
                 # Complex handlers with dependencies - use service references
+                - '@App\Form\Service\ParticipantTransportationDiscountReplacementFieldHandler'
                 - '@App\Form\Service\ParticipantBulkInsuranceFieldHandler'
                 - '@App\Form\Service\ParticipantInsuranceFieldHandler'
diff --git a/docs/PROJECT_OVERVIEW.md b/docs/PROJECT_OVERVIEW.md
index 1eb9f97..03accd2 100644
--- a/docs/PROJECT_OVERVIEW.md
+++ b/docs/PROJECT_OVERVIEW.md
@@ -231,6 +231,13 @@ Critical for correct pricing and auto-reassignment:
 - **Unified pickup field**: Single field for both directions (BPN API limitation)
 - **Conditional visibility**: Pickup vs parking fields mutually exclusive
 - **Direction mapping**: `DirectionMapper` translates API ↔ internal codes
+- **Discount replacement logic**: Automatic correction of incompatible transportation combinations
+  - When inbound bus selected with discounted PKW outbound: system automatically replaces with regular PKW
+  - When inbound changes from bus to PKW: system automatically restores discounted PKW if available
+  - Form options update dynamically to show only valid PKW variant
+  - User notified via toast messages about automatic changes
+  - Implemented via `ParticipantTransportationDiscountReplacementFieldHandler`
+  - Prevents invalid pricing where user gets both PKW discount and bus pricing
 
 ## Important Field Dependencies
 
@@ -430,8 +437,9 @@ Edit mode session requires proper cleanup to prevent dirty state persistence:
 - `src/Form/Service/EditFieldStateProvider.php` - Edit mode mutability constraints
 
 ### Field Handlers
-- `src/Form/Service/Participant*FieldHandler.php` (15+ handlers)
-- Transportation, pickup, parking, ski pass, rentals, insurance, bulk insurance, etc.
+- `src/Form/Service/Participant*FieldHandler.php` (16+ handlers)
+- Transportation (outbound, inbound, discount replacement), pickup, parking, ski pass, rentals, insurance, bulk insurance, etc.
+- `ParticipantTransportationDiscountReplacementFieldHandler` - Automatic discount replacement for invalid transportation combinations
 
 ## Testing
 
diff --git a/src/Form/Service/ParticipantFieldOptionsProvider.php b/src/Form/Service/ParticipantFieldOptionsProvider.php
index f111473..9d4a428 100644
--- a/src/Form/Service/ParticipantFieldOptionsProvider.php
+++ b/src/Form/Service/ParticipantFieldOptionsProvider.php
@@ -844,6 +844,16 @@ class ParticipantFieldOptionsProvider extends AbstractFieldOptionsProvider
 
         // If we have both discounted and regular options, apply smart filtering
         if (null !== $discountedPkw && null !== $regularPkw) {
+            // Get participant to check inbound transportation
+            $participant = $bookingDto->getParticipant($participantIndex);
+            $inboundIsBus = null !== $participant?->transportationInbound
+                && DirectionMapper::SUBTYPE_BUS_API === $participant->transportationInbound->subType;
+
+            // If inbound is BUS, always show regular PKW (not discounted)
+            if ($inboundIsBus) {
+                return [...$otherServices, $regularPkw];
+            }
+
             // Check if discounted option is unavailable for this participant (per-booking availability)
             $discountedIsUnavailable = $this->serviceAvailabilityCalculator->isServiceUnavailable(
                 $discountedPkw->id,
diff --git a/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php b/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php
new file mode 100644
index 0000000..b9fc1e9
--- /dev/null
+++ b/src/Form/Service/ParticipantTransportationDiscountReplacementFieldHandler.php
@@ -0,0 +1,156 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Form\Service;
+
+use App\BusProNet\Utility\DirectionMapper;
+use App\Form\Model\BookingDto;
+use App\Form\Service\Abstract\AbstractParticipantFieldHandler;
+use App\Service\ServiceAvailabilityCalculator;
+
+class ParticipantTransportationDiscountReplacementFieldHandler extends AbstractParticipantFieldHandler
+{
+    public function __construct(
+        private readonly ServiceAvailabilityCalculator $serviceAvailabilityCalculator,
+    ) {
+    }
+
+    public function getFieldName(): string
+    {
+        return 'transportationDiscountReplacement'; // Virtual field name
+    }
+
+    public function getDependencies(): array
+    {
+        return ['transportationOutbound', 'transportationInbound'];
+    }
+
+    public function shouldProcess(array $submittedData, string $mode, int $participantIndex): bool
+    {
+        return true; // Always process in all modes
+    }
+
+    /**
+     * Processes transportation discount replacement logic.
+     *
+     * Detects incompatible transportation combinations and automatically replaces
+     * discounted PKW with regular variant when inbound bus is selected. Also restores
+     * discounted PKW when inbound changes back to PKW and discount is still available.
+     *
+     * Business Rules:
+     * - Inbound BUS + Outbound discounted PKW → Replace with regular PKW (notification: warning)
+     * - Inbound PKW + Outbound regular PKW → Restore discounted PKW if available (notification: success)
+     * - Only processes PKW variants, never touches BUS or other services
+     */
+    public function processField(array $submittedData, BookingDto $bookingDto, int $participantIndex): void
+    {
+        // Step 1: Get participant and validate prerequisites
+        $participant = $bookingDto->getParticipant($participantIndex);
+        if (null === $participant) {
+            return;
+        }
+
+        // Need both transportation fields to process
+        if (null === $participant->transportationOutbound) {
+            return;
+        }
+
+        // Step 2: Detect inbound transportation type
+        $inboundIsBus = null !== $participant->transportationInbound
+            && DirectionMapper::SUBTYPE_BUS_API === $participant->transportationInbound->subType;
+
+        // Step 3: Get all outbound PKW services
+        // Get ALL outbound services (not filtered by availability or smart filtering)
+        $allOutboundServices = $bookingDto->travel->getTransportationServicesByDirection(
+            DirectionMapper::OUTBOUND_TRAVEL,
+            false // Do NOT filter by per-booking availability
+        );
+
+        // Find discounted and regular PKW services
+        $discountedPkw = null;
+        $regularPkw = null;
+
+        foreach ($allOutboundServices as $service) {
+            if (false === DirectionMapper::isCar($service->subType)) {
+                continue; // Skip non-PKW services
+            }
+
+            if (null !== $service->price && $service->price < 0) {
+                $discountedPkw = $service;
+            } elseif (null === $service->price || $service->price >= 0) {
+                $regularPkw = $service;
+            }
+        }
+
+        // Edge case: no regular PKW found (impossible in production, but handle gracefully)
+        if (null === $regularPkw) {
+            return;
+        }
+
+        // Step 4a: Handle inbound BUS scenario (force regular PKW)
+        if (true === $inboundIsBus) {
+            // Check if outbound is currently DISCOUNTED PKW
+            $outboundIsDiscountedPkw = DirectionMapper::isCar($participant->transportationOutbound->subType)
+                && null !== $participant->transportationOutbound->price
+                && $participant->transportationOutbound->price < 0;
+
+            if ($outboundIsDiscountedPkw) {
+                // Store original for notification
+                $originalLabel = $participant->transportationOutbound->label;
+
+                // Replace with regular PKW
+                $participant->transportationOutbound = $regularPkw;
+
+                // Notify user about replacement
+                $participant->addNotification(
+                    'warning',
+                    sprintf(
+                        'Hinfahrt automatisch angepasst: Rabattierte Anreise nicht möglich bei Busrückfahrt. Geändert von "%s" zu "%s".',
+                        $originalLabel,
+                        $regularPkw->label
+                    )
+                );
+            }
+
+            return; // Done processing for BUS inbound scenario
+        }
+
+        // Step 4b: Handle non-BUS inbound scenario (restore discount if available)
+        // Inbound is NOT BUS - try to restore discounted PKW if available
+
+        // Check if outbound is currently REGULAR PKW
+        $outboundIsRegularPkw = DirectionMapper::isCar($participant->transportationOutbound->subType)
+            && (null === $participant->transportationOutbound->price
+                || $participant->transportationOutbound->price >= 0);
+
+        if (false === $outboundIsRegularPkw || null === $discountedPkw) {
+            return; // Not eligible for discount restoration
+        }
+
+        // Check per-booking availability of discounted PKW
+        $discountedIsAvailable = false === $this->serviceAvailabilityCalculator->isServiceUnavailable(
+            $discountedPkw->id,
+            $bookingDto,
+            $participantIndex
+        );
+
+        if ($discountedIsAvailable) {
+            // Store original for notification
+            $originalLabel = $participant->transportationOutbound->label;
+
+            // Restore discounted PKW
+            $participant->transportationOutbound = $discountedPkw;
+
+            // Notify user about restoration
+            $participant->addNotification(
+                'success',
+                sprintf(
+                    'Hinfahrt automatisch angepasst: Rabattierte Anreise wieder verfügbar. Geändert von "%s" zu "%s".',
+                    $originalLabel,
+                    $discountedPkw->label
+                )
+            );
+        }
+    }
+}
diff --git a/tests/Form/Service/ParticipantTransportationDiscountReplacementFieldHandlerTest.php b/tests/Form/Service/ParticipantTransportationDiscountReplacementFieldHandlerTest.php
new file mode 100644
index 0000000..7139718
--- /dev/null
+++ b/tests/Form/Service/ParticipantTransportationDiscountReplacementFieldHandlerTest.php
@@ -0,0 +1,346 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Form\Service;
+
+use App\BusProNet\Model\Service;
+use App\BusProNet\Model\Travel;
+use App\BusProNet\Utility\DirectionMapper;
+use App\Form\Model\BookingDto;
+use App\Form\Model\ParticipantDto;
+use App\Form\Service\ParticipantTransportationDiscountReplacementFieldHandler;
+use App\Service\ServiceAvailabilityCalculator;
+use PHPUnit\Framework\TestCase;
+
+class ParticipantTransportationDiscountReplacementFieldHandlerTest extends TestCase
+{
+    private ParticipantTransportationDiscountReplacementFieldHandler $handler;
+    private ServiceAvailabilityCalculator $serviceAvailabilityCalculator;
+
+    protected function setUp(): void
+    {
+        $this->serviceAvailabilityCalculator = $this->createMock(ServiceAvailabilityCalculator::class);
+        $this->handler = new ParticipantTransportationDiscountReplacementFieldHandler(
+            $this->serviceAvailabilityCalculator
+        );
+    }
+
+    public function testGetFieldName(): void
+    {
+        $this->assertSame('transportationDiscountReplacement', $this->handler->getFieldName());
+    }
+
+    public function testGetDependencies(): void
+    {
+        $this->assertSame(['transportationOutbound', 'transportationInbound'], $this->handler->getDependencies());
+    }
+
+    public function testShouldProcessAlwaysReturnsTrue(): void
+    {
+        $this->assertTrue($this->handler->shouldProcess([], BookingDto::MODE_CREATE, 0));
+        $this->assertTrue($this->handler->shouldProcess(['some' => 'data'], BookingDto::MODE_EDIT, 5));
+    }
+
+    public function testProcessFieldReplacesDiscountedWithRegularWhenInboundIsBus(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+        $busInbound = $this->createBusService(200, 'Bus', DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup participant with discounted PKW outbound and BUS inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $discountedPkw;
+        $participant->transportationInbound = $busInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw, $busInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound was replaced with regular PKW
+        $this->assertSame($regularPkw->id, $participant->transportationOutbound->id);
+        $this->assertSame($regularPkw->label, $participant->transportationOutbound->label);
+
+        // Assert notification was generated
+        $this->assertCount(1, $participant->notifications);
+        $notification = reset($participant->notifications); // Get first notification (keyed by MD5 hash)
+        $this->assertSame('warning', $notification['type']);
+        $this->assertStringContainsString('Hinfahrt automatisch angepasst', $notification['message']);
+        $this->assertStringContainsString('Selbstorganisiert (-15€ Rabatt)', $notification['message']);
+        $this->assertStringContainsString('Selbstorganisiert', $notification['message']);
+    }
+
+    public function testProcessFieldRestoresDiscountedPkwWhenInboundChangesToPkw(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+        $pkwInbound = $this->createPkwService(201, 'Selbstorganisiert', 0.0, DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup participant with regular PKW outbound and PKW inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $regularPkw;
+        $participant->transportationInbound = $pkwInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw, $pkwInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        // Mock availability: discounted PKW is available
+        $this->serviceAvailabilityCalculator
+            ->expects($this->once())
+            ->method('isServiceUnavailable')
+            ->with($discountedPkw->id, $bookingDto, 0)
+            ->willReturn(false);
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound was replaced with discounted PKW
+        $this->assertSame($discountedPkw->id, $participant->transportationOutbound->id);
+        $this->assertSame($discountedPkw->label, $participant->transportationOutbound->label);
+
+        // Assert notification was generated
+        $this->assertCount(1, $participant->notifications);
+        $notification = reset($participant->notifications); // Get first notification (keyed by MD5 hash)
+        $this->assertSame('success', $notification['type']);
+        $this->assertStringContainsString('Hinfahrt automatisch angepasst', $notification['message']);
+        $this->assertStringContainsString('wieder verfügbar', $notification['message']);
+    }
+
+    public function testProcessFieldDoesNotRestoreDiscountWhenUnavailable(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+        $pkwInbound = $this->createPkwService(201, 'Selbstorganisiert', 0.0, DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup participant with regular PKW outbound and PKW inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $regularPkw;
+        $participant->transportationInbound = $pkwInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw, $pkwInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        // Mock availability: discounted PKW is sold out
+        $this->serviceAvailabilityCalculator
+            ->expects($this->once())
+            ->method('isServiceUnavailable')
+            ->with($discountedPkw->id, $bookingDto, 0)
+            ->willReturn(true);
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound remains regular PKW
+        $this->assertSame($regularPkw, $participant->transportationOutbound);
+
+        // Assert no notification was generated
+        $this->assertEmpty($participant->notifications);
+    }
+
+    public function testProcessFieldNoReplacementWhenOutboundIsBus(): void
+    {
+        // Setup services
+        $busOutbound = $this->createBusService(100, 'Bus', DirectionMapper::OUTBOUND_TRAVEL);
+        $busInbound = $this->createBusService(200, 'Bus', DirectionMapper::INBOUND_TRAVEL);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+
+        // Setup participant with BUS outbound and BUS inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $busOutbound;
+        $participant->transportationInbound = $busInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$busOutbound, $regularPkw, $busInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound remains BUS (no replacement)
+        $this->assertSame($busOutbound, $participant->transportationOutbound);
+
+        // Assert no notification was generated
+        $this->assertEmpty($participant->notifications);
+    }
+
+    public function testProcessFieldNoReplacementWhenOutboundIsRegularPkwAndInboundIsBus(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+        $busInbound = $this->createBusService(200, 'Bus', DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup participant with regular PKW outbound and BUS inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $regularPkw;
+        $participant->transportationInbound = $busInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw, $busInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound remains regular PKW (already correct)
+        $this->assertSame($regularPkw, $participant->transportationOutbound);
+
+        // Assert no notification was generated
+        $this->assertEmpty($participant->notifications);
+    }
+
+    public function testProcessFieldNoReplacementWhenOutboundIsDiscountedAndInboundIsPkw(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+        $pkwInbound = $this->createPkwService(201, 'Selbstorganisiert', 0.0, DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup participant with discounted PKW outbound and PKW inbound (optimal state)
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $discountedPkw;
+        $participant->transportationInbound = $pkwInbound;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw, $pkwInbound]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        $submittedData = [];
+
+        // Process
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound remains discounted PKW (already optimal)
+        $this->assertSame($discountedPkw, $participant->transportationOutbound);
+
+        // Assert no notification was generated
+        $this->assertEmpty($participant->notifications);
+    }
+
+    public function testProcessFieldHandlesNullOutbound(): void
+    {
+        // Setup participant with null outbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = null;
+        $participant->transportationInbound = $this->createBusService(200, 'Bus', DirectionMapper::INBOUND_TRAVEL);
+
+        // Setup booking
+        $travel = new Travel();
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        $submittedData = [];
+
+        // Process - should handle gracefully
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert no error and no notification
+        $this->assertNull($participant->transportationOutbound);
+        $this->assertEmpty($participant->notifications);
+    }
+
+    public function testProcessFieldHandlesNullInbound(): void
+    {
+        // Setup services
+        $discountedPkw = $this->createPkwService(100, 'Selbstorganisiert (-15€ Rabatt)', -15.0);
+        $regularPkw = $this->createPkwService(101, 'Selbstorganisiert', 0.0);
+
+        // Setup participant with regular PKW outbound and null inbound
+        $participant = new ParticipantDto();
+        $participant->transportationOutbound = $regularPkw;
+        $participant->transportationInbound = null;
+
+        // Setup booking with travel services
+        $travel = $this->createTravelWithServices([$discountedPkw, $regularPkw]);
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [$participant];
+
+        // Mock availability: discounted PKW is available
+        $this->serviceAvailabilityCalculator
+            ->expects($this->once())
+            ->method('isServiceUnavailable')
+            ->with($discountedPkw->id, $bookingDto, 0)
+            ->willReturn(false);
+
+        $submittedData = [];
+
+        // Process - null inbound is treated as non-BUS, should attempt restoration
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Assert outbound was replaced with discounted PKW
+        $this->assertSame($discountedPkw->id, $participant->transportationOutbound->id);
+        $this->assertSame($discountedPkw->label, $participant->transportationOutbound->label);
+    }
+
+    public function testProcessFieldHandlesNullParticipant(): void
+    {
+        // Setup booking with no participants
+        $travel = new Travel();
+        $bookingDto = new BookingDto($travel, 1);
+        $bookingDto->participants = [];
+
+        $submittedData = [];
+
+        // Process - should handle gracefully
+        $this->handler->processField($submittedData, $bookingDto, 0);
+
+        // Should not throw error
+        $this->expectNotToPerformAssertions();
+    }
+
+    private function createPkwService(int $id, string $label, float $price, string $direction = DirectionMapper::OUTBOUND_TRAVEL): Service
+    {
+        $service = new Service();
+        $service->id = $id;
+        $service->label = $label;
+        $service->subType = DirectionMapper::SUBTYPE_CAR_API; // 'PKW'
+        $service->direction = $direction;
+        $service->price = $price;
+
+        return $service;
+    }
+
+    private function createBusService(int $id, string $label, string $direction): Service
+    {
+        $service = new Service();
+        $service->id = $id;
+        $service->label = $label;
+        $service->subType = DirectionMapper::SUBTYPE_BUS_API; // 'BUS'
+        $service->direction = $direction;
+        $service->price = 0.0;
+
+        return $service;
+    }
+
+    private function createTravelWithServices(array $services): Travel
+    {
+        $travel = new Travel();
+        $travel->transportationServices = $services;
+
+        return $travel;
+    }
+}