diff --git a/pufferlib/ocean/drive/drive.h b/pufferlib/ocean/drive/drive.h
index 329e1bdf76..a95bae7885 100644
--- a/pufferlib/ocean/drive/drive.h
+++ b/pufferlib/ocean/drive/drive.h
@@ -86,6 +86,7 @@
 #define DEFAULT_DTC 50.0f                         // Ignore candidates beyond this range
 #define STOP_LINE_EXTENSION_FACTOR 1.5f
 #define RED_LIGHT_HEADING_THRESHOLD (M_PI / 4.0f)
+#define NUPLAN_BEHIND_COS_THRESHOLD -0.8660254f // cos(150 degrees)
 
 // TTC default value when no vehicle ahead
 #define DEFAULT_TTC 5.0f
@@ -100,6 +101,14 @@
 #define MULTI_LANE_FULL_SCORE_TIME 3.4f                        // seconds
 #define MULTI_LANE_HALF_SCORE_TIME 5.7f                        // seconds
 
+// nuPlan-style collision classification
+#define COLLISION_TYPE_NONE 0
+#define COLLISION_TYPE_STOPPED_EGO 1
+#define COLLISION_TYPE_STOPPED_TRACK 2
+#define COLLISION_TYPE_ACTIVE_REAR 3
+#define COLLISION_TYPE_ACTIVE_FRONT 4
+#define COLLISION_TYPE_ACTIVE_LATERAL 5
+
 // Collision/Infraction behaviors
 #define STOP_AGENT 1
 #define REMOVE_AGENT 2
@@ -2007,7 +2016,7 @@ static bool check_line_intersection(float p1[2], float p2[2], float q1[2], float
     return (s >= 0 && s <= 1 && t >= 0 && t <= 1);
 }
 
-static void compute_agent_corners(Agent *agent, float corners[4][2]) {
+static void compute_agent_corners(const Agent *agent, float corners[4][2]) {
     static const float offsets[4][2] = {{1, 1}, {1, -1}, {-1, -1}, {-1, 1}};
     float half_length = agent->sim_length / 2.0f;
     float half_width = agent->sim_width / 2.0f;
@@ -2020,6 +2029,37 @@ static void compute_agent_corners(Agent *agent, float corners[4][2]) {
     }
 }
 
+// helpers for nuPlan's at-fault collision, you need to know if the front bumper was involed
+static bool point_inside_agent_box(float x, float y, const Agent *agent) {
+    float dx = x - agent->sim_x;
+    float dy = y - agent->sim_y;
+    float local_long = dx * agent->cos_heading + dy * agent->sin_heading;
+    float local_lat = -dx * agent->sin_heading + dy * agent->cos_heading;
+    return fabsf(local_long) <= 0.5f * agent->sim_length && fabsf(local_lat) <= 0.5f * agent->sim_width;
+}
+
+static bool segment_intersects_agent_box(float p1[2], float p2[2], const Agent *agent) {
+    if (point_inside_agent_box(p1[0], p1[1], agent) || point_inside_agent_box(p2[0], p2[1], agent)) {
+        return true;
+    }
+
+    float corners[4][2];
+    compute_agent_corners(agent, corners);
+    for (int i = 0; i < 4; i++) {
+        int next = (i + 1) % 4;
+        if (check_line_intersection(p1, p2, corners[i], corners[next])) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static bool front_bumper_intersects_agent(const Agent *ego, const Agent *other) {
+    float corners[4][2];
+    compute_agent_corners(ego, corners);
+    return segment_intersects_agent_box(corners[0], corners[1], other);
+}
+
 static bool check_agent_corners_cross_stop_line(float corners[4][2], TrafficControlElement *traffic) {
     float sl_dx = traffic->stop_line[3] - traffic->stop_line[0];
     float sl_dy = traffic->stop_line[4] - traffic->stop_line[1];
@@ -2280,30 +2320,68 @@ static int collision_check(Drive *env, int agent_idx) {
     return car_collided_with_index;
 }
 
+static bool is_agent_behind_rear_axle(const Agent *ego, const Agent *other) {
+    float rear_x = ego->sim_x - 0.5f * ego->sim_length * ego->cos_heading;
+    float rear_y = ego->sim_y - 0.5f * ego->sim_length * ego->sin_heading;
+    float dx = other->sim_x - rear_x;
+    float dy = other->sim_y - rear_y;
+    float dist = sqrtf(dx * dx + dy * dy);
+    if (dist < 1e-6f) {
+        return false;
+    }
+
+    float dot = (ego->cos_heading * dx + ego->sin_heading * dy) / dist;
+    return dot < NUPLAN_BEHIND_COS_THRESHOLD;
+}
+
+static bool is_agent_cleanly_in_lane(const Agent *agent) {
+    if (agent->current_lane_idx == -1) {
+        return false;
+    }
+
+    float edge_dist = fabsf(agent->metrics_array[LANE_DIST_IDX]) + 0.5f * agent->sim_width;
+    return edge_dist <= MULTI_LANE_THRESHOLD;
+}
+
+static int classify_collision_type(const Agent *ego, const Agent *other) {
+    if (ego->sim_speed <= AGENT_STOPPED_SPEED_THRESHOLD) {
+        return COLLISION_TYPE_STOPPED_EGO;
+    }
+
+    if (other->sim_speed <= AGENT_STOPPED_SPEED_THRESHOLD) {
+        return COLLISION_TYPE_STOPPED_TRACK;
+    }
+
+    if (is_agent_behind_rear_axle(ego, other)) {
+        return COLLISION_TYPE_ACTIVE_REAR;
+    }
+
+    if (front_bumper_intersects_agent(ego, other)) {
+        return COLLISION_TYPE_ACTIVE_FRONT;
+    }
+
+    return COLLISION_TYPE_ACTIVE_LATERAL;
+}
+
 // Classify whether a collision is at-fault for the ego agent.
 static bool is_at_fault_collision(Drive *env, int agent_idx, int other_idx) {
     Agent *agent = &env->agents[agent_idx];
     Agent *other = &env->agents[other_idx];
+    int collision_type = classify_collision_type(agent, other);
 
-    // Rule 1: Collision with stopped vehicle = always at-fault.
-    if (other->sim_speed < AGENT_STOPPED_SPEED_THRESHOLD) {
+    if (collision_type == COLLISION_TYPE_STOPPED_TRACK) {
         return true;
     }
-    // Rule 2: If ego is stopped = never at-fault.
-    if (agent->sim_speed < AGENT_STOPPED_SPEED_THRESHOLD) {
-        return false;
+
+    if (collision_type == COLLISION_TYPE_ACTIVE_FRONT) {
+        return true;
     }
 
-    // Rule 3: Rear-bumper collision = not at-fault.
-    // Check if the other car hit our rear using the heading-aligned relative position.
-    float dx = other->sim_x - agent->sim_x;
-    float dy = other->sim_y - agent->sim_y;
-    float dot = dx * agent->cos_heading + dy * agent->sin_heading;
-    if (dot < 0) {
-        return false;
+    if (collision_type == COLLISION_TYPE_ACTIVE_LATERAL) {
+        return !is_agent_cleanly_in_lane(agent);
     }
 
-    return true;
+    return false;
 }
 
 static inline void ttc_update_min_result(Agent *ego, int other_idx, float closing_speed, float ttc) {