craftbukkit/nms-patches/net/minecraft/world/entity/vehicle/OldMinecartBehavior.patch

--- a/net/minecraft/world/entity/vehicle/OldMinecartBehavior.java
+++ b/net/minecraft/world/entity/vehicle/OldMinecartBehavior.java
@@ -25,6 +25,11 @@
 import net.minecraft.world.phys.AxisAlignedBB;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import org.bukkit.entity.Vehicle;
+import org.bukkit.event.vehicle.VehicleEntityCollisionEvent;
+// CraftBukkit end
+
 public class OldMinecartBehavior extends MinecartBehavior {
 
     private static final double MINECART_RIDABLE_THRESHOLD = 0.01D;
@@ -454,8 +459,26 @@
                     Entity entity = (Entity) iterator.next();
 
                     if (!(entity instanceof EntityHuman) && !(entity instanceof EntityIronGolem) && !(entity instanceof EntityMinecartAbstract) && !this.minecart.isVehicle() && !entity.isPassenger()) {
+                        // CraftBukkit start
+                        VehicleEntityCollisionEvent collisionEvent = new VehicleEntityCollisionEvent((Vehicle) this.minecart.getBukkitEntity(), entity.getBukkitEntity());
+                        this.level().getCraftServer().getPluginManager().callEvent(collisionEvent);
+
+                        if (collisionEvent.isCancelled()) {
+                            continue;
+                        }
+                        // CraftBukkit end
                         entity.startRiding(this.minecart);
                     } else {
+                        // CraftBukkit start
+                        if (!this.minecart.isPassengerOfSameVehicle(entity)) {
+                            VehicleEntityCollisionEvent collisionEvent = new VehicleEntityCollisionEvent((Vehicle) this.minecart.getBukkitEntity(), entity.getBukkitEntity());
+                            this.level().getCraftServer().getPluginManager().callEvent(collisionEvent);
+
+                            if (collisionEvent.isCancelled()) {
+                                continue;
+                            }
+                        }
+                        // CraftBukkit end
                         entity.push((Entity) this.minecart);
                     }
                 }
@@ -467,6 +490,14 @@
                 Entity entity1 = (Entity) iterator1.next();
 
                 if (!this.minecart.hasPassenger(entity1) && entity1.isPushable() && entity1 instanceof EntityMinecartAbstract) {
+                    // CraftBukkit start
+                    VehicleEntityCollisionEvent collisionEvent = new VehicleEntityCollisionEvent((Vehicle) this.minecart.getBukkitEntity(), entity1.getBukkitEntity());
+                    this.level().getCraftServer().getPluginManager().callEvent(collisionEvent);
+
+                    if (collisionEvent.isCancelled()) {
+                        continue;
+                    }
+                    // CraftBukkit end
                     entity1.push((Entity) this.minecart);
                 }
             }
@@ -487,11 +518,17 @@
 
     @Override
     public double getMaxSpeed(WorldServer worldserver) {
+        // CraftBukkit start
+        Double maxSpeed = this.minecart.maxSpeed;
+        if (maxSpeed != null) {
+            return (this.minecart.isInWater() ? maxSpeed / 2.0D : maxSpeed);
+        }
+        // CraftBukkit end
         return this.minecart.isInWater() ? 0.2D : 0.4D;
     }
 
     @Override
     public double getSlowdownFactor() {
-        return this.minecart.isVehicle() ? 0.997D : 0.96D;
+        return this.minecart.isVehicle() || !this.minecart.slowWhenEmpty ? 0.997D : 0.96D; // CraftBukkit - add !this.slowWhenEmpty
     }
 }