diff --git a/editor/src/plugins/scenarios.rs b/editor/src/plugins/scenarios.rs
index 069832ce70..94c43f3a57 100644
--- a/editor/src/plugins/scenarios.rs
+++ b/editor/src/plugins/scenarios.rs
@@ -116,7 +116,8 @@ fn edit_scenario(map: &Map, scenario: &mut Scenario, mut wizard: WrappedWizard)
     if wizard.choose_string("What kind of edit?", vec![seed_parked, spawn])? == seed_parked {
         scenario.seed_parked_cars.push(SeedParkedCars {
             neighborhood: choose_neighborhood(map, &mut wizard, "Seed parked cars in what area?")?,
-            percent_to_fill: wizard.input_percent("What percent of parking spots to populate?")?,
+            percent_buildings_with_car: wizard
+                .input_percent("What percent of buildings have 1 parked car nearby?")?,
         });
         Some(())
     } else {
diff --git a/sim/src/scenario.rs b/sim/src/scenario.rs
index 53d63b30db..d5ee20aa9f 100644
--- a/sim/src/scenario.rs
+++ b/sim/src/scenario.rs
@@ -29,7 +29,8 @@ pub struct SpawnOverTime {
 #[derive(Clone, Serialize, Deserialize, Debug)]
 pub struct SeedParkedCars {
     pub neighborhood: String,
-    pub percent_to_fill: f64,
+    // TODO Ask for more detail -- chances of a building have 0, 1, 2, 3, ... cars
+    pub percent_buildings_with_car: f64,
 }
 
 #[derive(Clone, Serialize, Deserialize, Debug)]
@@ -98,7 +99,7 @@ impl Scenario {
             sim.seed_parked_cars(
                 neighborhoods[&s.neighborhood].find_matching_lanes(map),
                 &bldgs_per_neighborhood[&s.neighborhood],
-                s.percent_to_fill,
+                s.percent_buildings_with_car,
             );
         }
 
diff --git a/sim/src/spawn.rs b/sim/src/spawn.rs
index 97964cc80d..2b5e0a2253 100644
--- a/sim/src/spawn.rs
+++ b/sim/src/spawn.rs
@@ -209,41 +209,49 @@ impl Spawner {
     // This happens immediately; it isn't scheduled.
     pub fn seed_parked_cars(
         &mut self,
-        percent_capacity_to_fill: f64,
+        percent_buildings_with_one_car: f64,
         in_lanes: Vec<LaneID>,
         owner_buildings: &Vec<BuildingID>,
         parking_sim: &mut ParkingSimState,
         base_rng: &mut XorShiftRng,
     ) {
-        assert!(percent_capacity_to_fill >= 0.0 && percent_capacity_to_fill <= 1.0);
+        assert!(percent_buildings_with_one_car >= 0.0 && percent_buildings_with_one_car <= 1.0);
 
-        let mut total_capacity = 0;
-        let mut new_cars = 0;
-        // Fork a new RNG for each candidate lane. This keeps things more deterministic, invariant
-        // of lane edits.
+        // TODO This is probably temporary.
+        let mut all_open_spots: Vec<ParkingSpot> = Vec::new();
         for l in in_lanes.into_iter() {
-            let mut rng = fork_rng(base_rng);
+            all_open_spots.extend(parking_sim.get_free_spots(l));
+        }
+        fork_rng(base_rng).shuffle(&mut all_open_spots);
+        let total_spots = all_open_spots.len();
 
-            for spot in parking_sim.get_free_spots(l) {
-                total_capacity += 1;
-                if rng.gen_bool(percent_capacity_to_fill) {
-                    new_cars += 1;
-                    let car = CarID(self.car_id_counter);
-                    // TODO since spawning applies during the next step, lots of stuff breaks without
-                    // this :(
-                    parking_sim.add_parked_car(ParkedCar::new(
-                        car,
-                        spot,
-                        Vehicle::generate_typical_car(car, &mut rng),
-                        Some(*rng.choose(owner_buildings).unwrap()),
-                    ));
-                    self.car_id_counter += 1;
-                }
+        let mut new_cars = 0;
+        for b in owner_buildings {
+            if base_rng.gen_bool(percent_buildings_with_one_car) {
+                // Pick a parking spot for this building.
+                // TODO Prefer spots closer to the building
+                let spot = all_open_spots
+                    .pop()
+                    .expect("No available parking spots left to seed");
+                new_cars += 1;
+                let car = CarID(self.car_id_counter);
+                // TODO since spawning applies during the next step, lots of stuff breaks without
+                // this :(
+                parking_sim.add_parked_car(ParkedCar::new(
+                    car,
+                    spot,
+                    Vehicle::generate_typical_car(car, base_rng),
+                    Some(*b),
+                ));
+                self.car_id_counter += 1;
             }
         }
+
         info!(
-            "Seeded {} of {} parking spots with cars",
-            new_cars, total_capacity
+            "Seeded {} of {} parking spots with cars, leaving {} buildings without cars",
+            new_cars,
+            total_spots,
+            owner_buildings.len() - new_cars
         );
     }