From 738f50f5b8c53c38a5ab89166eb67ee3f99b4a44 Mon Sep 17 00:00:00 2001
From: Dustin Carlino <dabreegster@gmail.com>
Date: Sun, 1 May 2022 17:01:18 +0100
Subject: [PATCH] Prevent pedestrians from endlessly cutting off cars at a stop
 sign by limiting how long a crowd can enter a crosswalk. #517

Removing Tehran from prebaking; it starts gridlocking. I didn't
investigate why; making SMP realistic unfortunately takes priority right
now.
---
 apps/game/src/challenges/prebake.rs       |  3 ++-
 sim/src/lib.rs                            |  4 +++
 sim/src/mechanics/intersection.rs         | 33 ++++++++++++++++++++++-
 tests/goldenfiles/prebaked_summaries.json | 13 +++------
 4 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/apps/game/src/challenges/prebake.rs b/apps/game/src/challenges/prebake.rs
index 808decb2a4..0feb4218ab 100644
--- a/apps/game/src/challenges/prebake.rs
+++ b/apps/game/src/challenges/prebake.rs
@@ -53,7 +53,8 @@ pub fn prebake_all() {
         }
     }
 
-    {
+    // Started gridlocking with more realistic pedestrian crossing behavior
+    if false {
         let tehran_map = map_model::Map::load_synchronously(
             MapName::new("ir", "tehran", "parliament").path(),
             &mut timer,
diff --git a/sim/src/lib.rs b/sim/src/lib.rs
index 21ef80af80..9698ed7d75 100644
--- a/sim/src/lib.rs
+++ b/sim/src/lib.rs
@@ -169,6 +169,10 @@ impl AgentID {
             _ => false,
         }
     }
+
+    pub(crate) fn is_pedestrian(&self) -> bool {
+        matches!(self, AgentID::Pedestrian(_))
+    }
 }
 
 impl fmt::Display for AgentID {
diff --git a/sim/src/mechanics/intersection.rs b/sim/src/mechanics/intersection.rs
index 2692dd9f88..ef449b6378 100644
--- a/sim/src/mechanics/intersection.rs
+++ b/sim/src/mechanics/intersection.rs
@@ -847,7 +847,7 @@ impl IntersectionSimState {
         req: &Request,
         map: &Map,
         sign: &ControlStopSign,
-        _speed: Speed,
+        speed: Speed,
         now: Time,
         scheduler: &mut Scheduler,
     ) -> bool {
@@ -881,6 +881,37 @@ impl IntersectionSimState {
         // TODO Make sure we can optimistically finish this turn before an approaching
         // higher-priority vehicle wants to begin.
 
+        // If a pedestrian is going to cut off a car, check how long the car has been waiting and
+        // maybe yield (regardless of stop sign priority). This is a very rough start to more
+        // realistic "batching" of pedestrians to cross a street. Without this, if there's one
+        // pedestrian almost clear of a crosswalk, cars are totally stopped for them, and so a new
+        // pedestrian arriving will win.
+        if req.agent.is_pedestrian() {
+            let our_turn = map.get_t(req.turn);
+            let time_to_cross = our_turn.geom.length() / speed;
+            for (other_req, (other_time, _)) in &self.state[&req.turn.parent].waiting {
+                if matches!(other_req.agent, AgentID::Car(_)) {
+                    if our_turn.conflicts_with(map.get_t(other_req.turn)) {
+                        let our_waiting = now - our_time;
+                        let other_waiting = now - *other_time;
+                        // We can't tell if a car has been waiting for a while due to pedestrians
+                        // crossing, or due to a blockage in their destination queue. Always let
+                        // pedestrians muscle their way in eventually.
+                        if our_waiting > other_waiting {
+                            continue;
+                        }
+                        // Intuition: another pedestrian trying to enter a crosswalk has a 3s
+                        // buffer to "join" the first pedestrian who started crossing and caused
+                        // cars to stop. We're using the time for _this_ pedestrian to cross _this_
+                        // turn, so it's a very rough definition.
+                        if other_waiting > time_to_cross + Duration::seconds(3.0) {
+                            return false;
+                        }
+                    }
+                }
+            }
+        }
+
         true
     }
 
diff --git a/tests/goldenfiles/prebaked_summaries.json b/tests/goldenfiles/prebaked_summaries.json
index 3c468f57a5..81faf024df 100644
--- a/tests/goldenfiles/prebaked_summaries.json
+++ b/tests/goldenfiles/prebaked_summaries.json
@@ -4,27 +4,20 @@
     "scenario": "weekday",
     "finished_trips": 76640,
     "cancelled_trips": 0,
-    "total_trip_duration_seconds": 43681790.01100022
+    "total_trip_duration_seconds": 43931256.87820016
   },
   {
     "map": "montlake (in seattle (us))",
     "scenario": "weekday",
     "finished_trips": 36710,
     "cancelled_trips": 86,
-    "total_trip_duration_seconds": 18533522.79990011
-  },
-  {
-    "map": "parliament (in tehran (ir))",
-    "scenario": "random people going to and from work",
-    "finished_trips": 29350,
-    "cancelled_trips": 16734,
-    "total_trip_duration_seconds": 40298148.80850012
+    "total_trip_duration_seconds": 18533435.094100088
   },
   {
     "map": "sao_miguel_paulista (in sao_paulo (br))",
     "scenario": "Full",
     "finished_trips": 122948,
     "cancelled_trips": 33043,
-    "total_trip_duration_seconds": 102103184.10710092
+    "total_trip_duration_seconds": 86387963.54580107
   }
 ]
\ No newline at end of file