diff --git a/src/train.h b/src/train.h
index 66386b5c6a..dd2b2734f4 100644
--- a/src/train.h
+++ b/src/train.h
@@ -493,4 +493,6 @@ inline int GetTrainStopLocation(StationID station_id, TileIndex tile, Train *v,
 	return GetTrainStopLocation(station_id, tile, v, update_train_state, station_ahead, station_length, v->x_pos, v->y_pos);
 }
 
+int GetTrainEstimatedMaxAchievableSpeed(const Train *train, const int mass, const int speed_cap);
+
 #endif /* TRAIN_H */
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index a208e32851..6cf27b064b 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -6919,3 +6919,62 @@ void TrainBrakesOverheatedBreakdown(Vehicle *v)
 	t->breakdown_type = BREAKDOWN_BRAKE_OVERHEAT;
 	t->breakdown_severity = 0;
 }
+
+static int GetTrainRealisticAccelerationAtSpeed(const Train *train, const int speed, const int mass)
+{
+	const int64 power = train->gcache.cached_power * 746ll;
+	int64 resistance = 0;
+
+	const bool maglev = (GetRailTypeInfo(train->railtype)->acceleration_type == 2);
+
+	if (!maglev) {
+		/* Static resistance plus rolling friction. */
+		resistance = 10 * mass;
+		resistance += mass * (15 * (512 + speed) / 512);
+	}
+
+	const int area = 14;
+
+	resistance += (area * train->gcache.cached_air_drag * speed * speed) / 1000;
+
+	uint32 max_te = train->gcache.cached_max_te; // [N]
+	int64 force;
+
+	if (speed > 0) {
+		if (!maglev) {
+			/* Conversion factor from km/h to m/s is 5/18 to get [N] in the end. */
+			force = power * 18 / (speed * 5);
+
+			if (force > static_cast<int>(max_te)) {
+				force = max_te;
+			}
+		} else {
+			force = power / 25;
+		}
+	} else {
+		force = (!maglev) ? std::min<uint64>(max_te, power) : power;
+		force = std::max(force, (mass * 8) + resistance);
+	}
+
+	/* Easy way out when there is no acceleration. */
+	if (force == resistance) return 0;
+
+	int acceleration = ClampToI32((force - resistance) / (mass * 4));
+	acceleration = force < resistance ? std::min(-1, acceleration) : std::max(1, acceleration);
+
+	return acceleration;
+}
+
+int GetTrainEstimatedMaxAchievableSpeed(const Train *train, const int mass, const int speed_cap)
+{
+	int max_speed = 0;
+	int acceleration;
+
+	do
+	{
+		max_speed++;
+		acceleration = GetTrainRealisticAccelerationAtSpeed(train, max_speed, mass);
+	} while (acceleration > 0 && max_speed < speed_cap);
+
+	return max_speed;
+}
diff --git a/src/train_gui.cpp b/src/train_gui.cpp
index 6985c01d5b..4b19e1effd 100644
--- a/src/train_gui.cpp
+++ b/src/train_gui.cpp
@@ -410,65 +410,6 @@ int GetTrainDetailsWndVScroll(VehicleID veh_id, TrainDetailsWindowTabs det_tab)
 	return num;
 }
 
-int GetAcceleration(const Train *train, const int speed, const int mass)
-{
-	const int64 power = train->gcache.cached_power * 746ll;
-	int64 resistance = 0;
-
-	const bool maglev = (GetRailTypeInfo(train->railtype)->acceleration_type == 2);
-
-	if (!maglev) {
-		/* Static resistance plus rolling friction. */
-		resistance = 10 * mass;
-		resistance += mass * (15 * (512 + speed) / 512);
-	}
-
-	const int area = 14;
-
-	resistance += (area * train->gcache.cached_air_drag * speed * speed) / 1000;
-
-	uint32 max_te = train->gcache.cached_max_te; // [N]
-	int64 force;
-
-	if (speed > 0) {
-		if (!maglev) {
-			/* Conversion factor from km/h to m/s is 5/18 to get [N] in the end. */
-			force = power * 18 / (speed * 5);
-
-			if (force > static_cast<int>(max_te)) {
-				force = max_te;
-			}
-		} else {
-			force = power / 25;
-		}
-	} else {
-		force = (!maglev) ? std::min<uint64>(max_te, power) : power;
-		force = std::max(force, (mass * 8) + resistance);
-	}
-
-	/* Easy way out when there is no acceleration. */
-	if (force == resistance) return 0;
-
-	int acceleration = ClampToI32((force - resistance) / (mass * 4));
-	acceleration = force < resistance ? std::min(-1, acceleration) : std::max(1, acceleration);
-
-	return acceleration;
-}
-
-int GetMaxSpeed(const Train *train, const int mass, const int speed_cap)
-{
-	int max_speed = 0;
-	int acceleration;
-	
-	do
-	{
-		max_speed++;
-		acceleration = GetAcceleration(train, max_speed, mass);
-	} while (acceleration > 0 && max_speed < speed_cap);
-
-	return max_speed;
-}
-
 /**
  * Draw the details for the given vehicle at the given position
  *
@@ -590,8 +531,8 @@ void DrawTrainDetails(const Train *v, int left, int right, int y, int vscroll_po
 		}
 
 		if (_settings_game.vehicle.train_acceleration_model != AM_ORIGINAL) {
-			const int empty_max_speed = GetMaxSpeed(v, empty_weight, v->GetDisplayMaxSpeed());
-			const int loaded_max_speed = GetMaxSpeed(v, loaded_weight, v->GetDisplayMaxSpeed());
+			const int empty_max_speed = GetTrainEstimatedMaxAchievableSpeed(v, empty_weight, v->GetDisplayMaxSpeed());
+			const int loaded_max_speed = GetTrainEstimatedMaxAchievableSpeed(v, loaded_weight, v->GetDisplayMaxSpeed());
 
 			if (--vscroll_pos < 0 && vscroll_pos >= -vscroll_cap) {
 				SetDParam(0, empty_weight);