diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -2630,38 +2630,14 @@ void Train::MarkDirty()
  */
 int Train::UpdateSpeed()
 {
-	uint accel;
-	uint16 max_speed;
-
 	switch (_settings_game.vehicle.train_acceleration_model) {
 		default: NOT_REACHED();
 		case AM_ORIGINAL:
-			max_speed = this->gcache.cached_max_track_speed;
-			accel = this->acceleration * (this->GetAccelerationStatus() == AS_BRAKE ? -4 : 2);
-			break;
+			return this->DoUpdateSpeed(this->acceleration * (this->GetAccelerationStatus() == AS_BRAKE ? -4 : 2), 0, this->gcache.cached_max_track_speed);
+
 		case AM_REALISTIC:
-			max_speed = this->GetCurrentMaxSpeed();
-			accel = this->GetAcceleration();
-			break;
+			return this->DoUpdateSpeed(this->GetAcceleration(), this->GetAccelerationStatus() == AS_BRAKE ? 0 : 2, this->GetCurrentMaxSpeed());
 	}
-
-	uint spd = this->subspeed + accel;
-	this->subspeed = (byte)spd;
-	{
-		int tempmax = max_speed;
-		if (this->cur_speed > max_speed) {
-			tempmax = max(this->cur_speed - (this->cur_speed / 10) - 1, tempmax);
-		}
-		/* Force a minimum speed of 1 km/h when realistic acceleration is on and the train is not braking. */
-		int min_speed = (_settings_game.vehicle.train_acceleration_model == AM_ORIGINAL || this->GetAccelerationStatus() == AS_BRAKE) ? 0 : 2;
-		this->cur_speed = spd = Clamp(this->cur_speed + ((int)spd >> 8), min_speed, tempmax);
-	}
-
-	int scaled_spd = this->GetAdvanceSpeed(spd);
-
-	scaled_spd += this->progress;
-	this->progress = 0; // set later in TrainLocoHandler or TrainController
-	return scaled_spd;
 }
 
 /**