diff --git a/astar.go b/astar.go
index 7a4a860..83dea20 100644
--- a/astar.go
+++ b/astar.go
@@ -98,7 +98,7 @@ func (b *Bifrost) RouteOnlyTimeIndependent(rounds *Rounds, origins []SourceKey,
 
 	_, ok := rounds.EarliestArrivals[destKey]
 	if !ok {
-		panic("destination unreachable")
+		panic(NoRouteError(true))
 	}
 
 	journey := b.ReconstructJourney(destKey, 1, rounds)
diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..ebe3185
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,9 @@
+package bifrost
+
+import "fmt"
+
+type NoRouteError bool
+
+func (e NoRouteError) Error() string {
+	return fmt.Sprintf("no route found")
+}
diff --git a/raptor.go b/raptor.go
index 1e535ba..2642933 100644
--- a/raptor.go
+++ b/raptor.go
@@ -220,7 +220,7 @@ func (b *Bifrost) RouteTransit(rounds *Rounds, origins []SourceKey, destKey uint
 
 	_, ok = rounds.EarliestArrivals[destKey]
 	if !ok {
-		return nil, fmt.Errorf("destination unreachable")
+		return nil, NoRouteError(true)
 	}
 
 	journey := b.ReconstructJourney(destKey, lastRound, rounds)
diff --git a/server/main.go b/server/main.go
index 6e9a25c..18149ae 100644
--- a/server/main.go
+++ b/server/main.go
@@ -37,6 +37,19 @@ func (s *StringSlice) Set(value string) error {
 	return nil
 }
 
+func SemaphoreMiddleware(maxConcurrentRequests int) gin.HandlerFunc {
+	semaphore := make(chan bool, maxConcurrentRequests)
+
+	return func(c *gin.Context) {
+		semaphore <- true
+		defer func() {
+			<-semaphore
+		}()
+
+		c.Next()
+	}
+}
+
 func main() {
 	var osmPath StringSlice
 	var gtfsPath StringSlice
@@ -84,23 +97,13 @@ func main() {
 		*numHandlerThreads = roundChanSize
 	}
 
-	threadChan := make(chan bool, *numHandlerThreads)
-
-	for i := 0; i < *numHandlerThreads; i++ {
-		threadChan <- true
-	}
-
 	fmt.Println("Startup took", time.Since(start))
 
 	engine := gin.Default()
 
-	engine.POST("/bifrost", func(c *gin.Context) {
-		<-threadChan
-
-		defer func() {
-			threadChan <- true
-		}()
+	engine.Use(SemaphoreMiddleware(*numHandlerThreads))
 
+	engine.POST("/bifrost", func(c *gin.Context) {
 		handle(c, b)
 	})
 
@@ -112,13 +115,24 @@ func main() {
 
 func handle(c *gin.Context, b *bifrost.Bifrost) {
 	defer func() {
-		if r := recover(); r != nil {
-			fmt.Println("Recovered in f", r)
+		r := recover()
 
-			debug.PrintStack()
+		if r == nil {
+			return
+		}
 
-			c.String(500, "Internal server error: %v", r)
+		if _, ok := r.(bifrost.NoRouteError); ok {
+			c.JSON(404, gin.H{
+				"error": "no route found",
+			})
+			return
 		}
+
+		fmt.Println("Recovered in f", r)
+
+		debug.PrintStack()
+
+		c.String(500, "Internal server error: %v", r)
 	}()
 
 	req := &JourneyRequest{}