diff --git a/src/engine.cpp b/src/engine.cpp
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -675,7 +675,7 @@ void StartupOneEngine(Engine *e, Date ag
 	 * of engines in early starting games.
 	 * Note: TTDP uses fixed 1922 */
 	e->intro_date = ei->base_intro <= ConvertYMDToDate(_settings_game.game_creation.starting_year + 2, 0, 1) ? ei->base_intro : (Date)GB(r, 0, 9) + ei->base_intro;
-	if (e->intro_date <= _date) {
+	if (e->intro_date <= TimerGameCalendar::date) {
 		e->age = (aging_date - e->intro_date) >> 5;
 		e->company_avail = MAX_UVALUE(CompanyMask);
 		e->flags |= ENGINE_AVAILABLE;
@@ -721,7 +721,7 @@ void StartupOneEngine(Engine *e, Date ag
 void StartupEngines()
 {
 	/* Aging of vehicles stops, so account for that when starting late */
-	const Date aging_date = std::min(_date, ConvertYMDToDate(_year_engine_aging_stops, 0, 1));
+	const Date aging_date = std::min(TimerGameCalendar::date, ConvertYMDToDate(_year_engine_aging_stops, 0, 1));
 	uint32 seed = Random();
 
 	for (Engine *e : Engine::Iterate()) {
@@ -883,11 +883,11 @@ static bool IsVehicleTypeDisabled(Vehicl
 static IntervalTimer<TimerGameCalendar> _engines_daily({TimerGameCalendar::DAY, TimerGameCalendar::Priority::ENGINE}, [](auto)
 {
 	for (Company *c : Company::Iterate()) {
-		c->avail_railtypes = AddDateIntroducedRailTypes(c->avail_railtypes, _date);
-		c->avail_roadtypes = AddDateIntroducedRoadTypes(c->avail_roadtypes, _date);
+		c->avail_railtypes = AddDateIntroducedRailTypes(c->avail_railtypes, TimerGameCalendar::date);
+		c->avail_roadtypes = AddDateIntroducedRoadTypes(c->avail_roadtypes, TimerGameCalendar::date);
 	}
 
-	if (_cur_year >= _year_engine_aging_stops) return;
+	if (TimerGameCalendar::year >= _year_engine_aging_stops) return;
 
 	for (Engine *e : Engine::Iterate()) {
 		EngineID i = e->index;
@@ -1038,11 +1038,11 @@ static void NewVehicleAvailable(Engine *
 	if (e->type == VEH_TRAIN) {
 		/* maybe make another rail type available */
 		assert(e->u.rail.railtype < RAILTYPE_END);
-		for (Company *c : Company::Iterate()) c->avail_railtypes = AddDateIntroducedRailTypes(c->avail_railtypes | GetRailTypeInfo(e->u.rail.railtype)->introduces_railtypes, _date);
+		for (Company *c : Company::Iterate()) c->avail_railtypes = AddDateIntroducedRailTypes(c->avail_railtypes | GetRailTypeInfo(e->u.rail.railtype)->introduces_railtypes, TimerGameCalendar::date);
 	} else if (e->type == VEH_ROAD) {
 		/* maybe make another road type available */
 		assert(e->u.road.roadtype < ROADTYPE_END);
-		for (Company* c : Company::Iterate()) c->avail_roadtypes = AddDateIntroducedRoadTypes(c->avail_roadtypes | GetRoadTypeInfo(e->u.road.roadtype)->introduces_roadtypes, _date);
+		for (Company* c : Company::Iterate()) c->avail_roadtypes = AddDateIntroducedRoadTypes(c->avail_roadtypes | GetRoadTypeInfo(e->u.road.roadtype)->introduces_roadtypes, TimerGameCalendar::date);
 	}
 
 	/* Only broadcast event if AIs are able to build this vehicle type. */
@@ -1067,7 +1067,7 @@ static void NewVehicleAvailable(Engine *
 /** Monthly update of the availability, reliability, and preview offers of the engines. */
 void EnginesMonthlyLoop()
 {
-	if (_cur_year < _year_engine_aging_stops) {
+	if (TimerGameCalendar::year < _year_engine_aging_stops) {
 		bool refresh = false;
 		for (Engine *e : Engine::Iterate()) {
 			/* Age the vehicle */
@@ -1080,10 +1080,10 @@ void EnginesMonthlyLoop()
 			/* Do not introduce invalid engines */
 			if (!e->IsEnabled()) continue;
 
-			if (!(e->flags & ENGINE_AVAILABLE) && _date >= (e->intro_date + DAYS_IN_YEAR)) {
+			if (!(e->flags & ENGINE_AVAILABLE) && TimerGameCalendar::date >= (e->intro_date + DAYS_IN_YEAR)) {
 				/* Introduce it to all companies */
 				NewVehicleAvailable(e);
-			} else if (!(e->flags & (ENGINE_AVAILABLE | ENGINE_EXCLUSIVE_PREVIEW)) && _date >= e->intro_date) {
+			} else if (!(e->flags & (ENGINE_AVAILABLE | ENGINE_EXCLUSIVE_PREVIEW)) && TimerGameCalendar::date >= e->intro_date) {
 				/* Introduction date has passed...
 				 * Check if it is allowed to build this vehicle type at all
 				 * based on the current game settings. If not, it does not