diff --git a/control/src/lib.rs b/control/src/lib.rs
index d42f6890c1..93fc99123c 100644
--- a/control/src/lib.rs
+++ b/control/src/lib.rs
@@ -73,6 +73,8 @@ impl ControlMap {
     }
 }
 
+// General problem: TurnIDs change as code does. Serialized state is kinda tied to code version.
+
 #[derive(Serialize, Deserialize, Debug)]
 pub struct ModifiedTrafficSignal {
     pub cycles: Vec<CycleState>,
diff --git a/sim/src/intersections.rs b/sim/src/intersections.rs
index ae874edcf6..ff25356dd6 100644
--- a/sim/src/intersections.rs
+++ b/sim/src/intersections.rs
@@ -102,7 +102,7 @@ impl StopSign {
         map: &Map,
         control_map: &ControlMap,
     ) -> bool {
-        // TODO assert turn is in this intersection
+        assert_eq!(map.get_t(turn).parent, self.id);
 
         if self.accepted.contains_key(&car) {
             return true;
@@ -164,12 +164,14 @@ impl TrafficSignal {
     fn can_do_turn(
         &mut self,
         car: CarID,
-        turn: TurnID,
+        t: TurnID,
         time: Tick,
         map: &Map,
         control_map: &ControlMap,
     ) -> bool {
-        // TODO assert turn is in this intersection
+        let turn = map.get_t(t);
+
+        assert_eq!(turn.parent, self.id);
 
         if self.accepted.contains_key(&car) {
             return true;
@@ -178,15 +180,15 @@ impl TrafficSignal {
         let signal = &control_map.traffic_signals[&self.id];
         let (cycle, remaining_cycle_time) = signal.current_cycle_and_remaining_time(time.as_time());
 
-        if !cycle.contains(turn) {
+        if !cycle.contains(t) {
             return false;
         }
         // How long will it take the car to cross the turn?
-        let crossing_time = map.get_t(turn).length() / SPEED_LIMIT;
+        let crossing_time = turn.length() / SPEED_LIMIT;
         // TODO account for TIMESTEP
 
         if crossing_time < remaining_cycle_time {
-            self.accepted.insert(car, turn);
+            self.accepted.insert(car, t);
             return true;
         }