Stress Test Debug Tool

Stress Test Debug Tool turns a free game into a dense, busy map in minutes: big towns, lots of vehicles, heavy traffic, fast time. It is made for performance-testing mods (and the game) under load.

Warning: this tool changes your save (towns, vehicles, money, date). Use a copy of a save, for testing only. Never use it on a save you care about.

Features

A button in the top-left button row (a gauge icon, or the word "Debug") opens the window. Each section works like a form: pick the options, then press its green button. Actions run one after another from a queue (shown at the top of the window, with "Clear queue" to drop what is waiting); pressing a button again while its batch is still queued or running does nothing. Every action writes an [SQST] line to the window's log and to stdout.txt.

• Game: add 10M or 100M, keep the balance above 50M (checked every 2 s), jump to any year from 1850 to 2150, set the game speed up to 16x, and hide all notifications (on by default).
• Game: town ratings: make every town ignore noise and pollution (sets their rating sensitivity to zero, as the town editor does), or restore the default sensitivities.
• Towns: grow all towns or the one nearest the camera (x2 to x100) with 1 to 10 build-out passes for denser towns; spawn 1 to 25 new towns (Small to Huge) near the camera or spread over the map, optionally connected by road to their nearest town; freeze or unfreeze town development; a readout of towns, capacity and buildings.
• Towns: test grid: identical towns (same seed, size and street angle) at exact, equally spaced positions: 2 x 2, 3 x 3 or a row of 4, 1 to 6 km apart, around the map centre or the camera, optionally linked by road to their neighbours (and diagonals). Streets "Wide grid" first lays a square grid of large 4-lane town streets (400 to 800 m across, by town size) where each town goes, so the town grows along wide roads; "Wide grid, locked" also stops the town from changing or extending those streets, and makes the grid's outer ring a country road, so the town builds no houses outside it. For comparing traffic between towns on a flat map: start a Blank Slate map, remove its towns and roads, then create the grid and freeze the towns.
• Towns: junction test (with Roundabouts & Interchanges enabled): a grid of test towns with one of each of its junctions in the middle of every grid cell (Roundabout, Magic Roundabout, Channelized X and T, the Roundabout, Dumbbell and Peanut Interchanges, Parclo, Parclo 2 and Diamond; or only the roundabouts or only the interchanges), each arm linked by road to a corner town (highway arms by a highway, both carriageways all the way to the town). No other road joins the towns, so all traffic between them drives through the junctions. Towns 2 to 4 km apart, around the map centre or the camera, on a wide street grid (default) or their own streets; use an empty flat map. "Traffic: Bus lines" then adds two bus lines per junction between its opposite corner towns, so buses drive straight through it (the Crossing test gets four lines between its towns the same way).
• Towns: showcase (with Roundabouts & Interchanges enabled): one button fills the map with groups: one junction with a medium town on every arm (all towns the same size), close around it, groups not joined to each other. The junctions take turns: every interchange (highway arms reach their towns as highways), every roundabout, and plain game crossroads and T-junctions of ordinary streets (lanes per arm, angle and traffic lights drawn too), each with random settings from a new seed per press, written to the log. Every group is built side by side as identical twins, one with Smart Lanes and one left at the game default (lit plain crossings get a third twin for Smart Lanes light phases), so the two can be compared under the same traffic. With Smart Lanes enabled, the Showcase tells it each twin's zone before building, and Smart Lanes leaves the game-default twin alone and gives the third twin its light phases whatever its own setting; without Smart Lanes every twin stays at the game default. Every town street is locked against town changes (the wide street grid, the town's own first streets and the links to the junction; unused corner stubs are removed), so the towns stay inside their grids: after the links every town grows x10 with its buildings shifted to the higher levels, for a dense centre and no streets or houses outside the grid. Keep balance is switched on and bus lines across every group follow the build. Each group's zone is written to the log for the traffic log. Remove all roads and Remove towns (grid or all towns) clear the zones in Smart Lanes again.
• Towns: lights showcase: one button fills the map with every lit junction shape: 2x2 X, 3x3 X, 3x2 X (main road 3 lanes each way, side road 2) and a T junction with 2 lanes each way (lanes per direction, two-way country roads), three sets of each. Every junction is at 90 degrees and lined up with the map, with a medium town on each arm (north, east, south, west; a T has three), each linked by one straight large country road (3 lanes each way) into the middle of its grid's facing side. That point is a three-lane roundabout (two lanes where three does not fit) joined to the grid's outer ring and central street, so the town entry never holds up the traffic under test (the same in every twin; before 1940, the grid's crossroads). Where a road meets a road with more lanes, its outer lane feeds all the extra ones and they all lead back into it, so no lane on a link ends blind. The traffic light is asked for at every junction (from 1950 the game also places its own; before 1950 a dialog warns, and a junction without a light gets one). Every set is built three times side by side with identical settings: Smart Lanes, the game default and Smart Lanes with every turn fanned into the exit lanes at the light (game phases; without Smart Lanes all three stay at the game default). As in the Showcase the town streets are locked to their grids; after the links every town grows once with higher building levels to about 400 people (each town from its own capacity), denser and taller, not wider. No bus lines: the towns' own traffic. A new seed per press, Keep balance switched on, all 12 sets, with every twin once in every position per shape for a fair comparison, need a 20 km map (36 junctions, 135 towns; a 16 km map holds 6 sets, positions not balanced); the traffic log follows it like the Showcase, and now also counts the cars through each junction per minute and splits each arm's queue into the side towards and away from the junction.
• Towns: remove towns: destroy the town nearest the camera, the test towns (of the test grid, the Junction and Crossing tests and both Showcases, found by name and, in the session that made them, by the town itself), or all towns, together with their streets and buildings (the game's own town removal, as the map editor uses it). Asks for confirmation first and cannot be undone.
• Towns: remove all roads: remove every street on the map, town streets and your own roads (streets that are part of a station, depot or other construction stay; tracks are not touched). Asks for confirmation first and cannot be undone. Towns rebuild their streets while they develop, so remove or freeze the towns first.
• Traffic: add vehicles: buy 1 to 25 copies of each line's first vehicle for all your lines (at the line's depot, one at a time; stops when the money runs out), and sell the vehicles added this session.
• Traffic: clear traffic: send every car driver home at once (uses one of the game's debug commands; your own vehicles are never touched). Drivers start new trips after a few seconds, so "Keep traffic cleared" repeats it every 2, 5, 10, 60 or 120 seconds (the longer intervals let traffic build up between clears). "Where" limits it to cars in towns (traffic between towns, for example through the junction test's junctions, keeps driving) or to cars outside towns.
• Traffic: auto bus lines: for the town nearest the camera, the 5 nearest or all towns (up to 25), 1, 2 or 4 lines per town. Each town first gets a road depot (one of yours nearby, or a new one built and connected to the streets; a town where none fits is skipped with nothing built), then two bus stops 300-800 m apart on its streets, a line between them and 2, 5 or 10 of the newest buses. "Remove added bus lines" sells those buses, waits until they are gone, then deletes the lines made this session (also those of the Junction and Crossing test's Traffic).
• Traffic: traffic log: every 10, 30 or 60 game seconds (none while paused) writes the traffic of every Showcase junction twin (every car driving on the map is read: cars in the junction and on each of its approach roads out to 200 m beyond it, mean and median speed, standing and queued cars, queued cars per approach, how long they stand), the whole map, every Showcase and Lights showcase bus line (round trips) and the towns' traffic ratings to stdout.txt as [SQST] FLOW lines, for a Smart Lanes / game default comparison of the twins. After a reload the zones come from Smart Lanes (when enabled). It only reads, spread over frames so the game keeps running smoothly; it warns when Keep traffic cleared is on, which would empty the roads. The tool's make flow report (in its source repository) turns the lines into per-pair tables.
• Traffic: readout: lines, vehicles, sim persons and cars driving at the last clear.
• Probe tab (opt-in, see Settings): the in-game experiments the tool was built from, for mod developers. Every probe button changes your save.

Settings

Load-time settings in the mod's options when you load or start a game (choose Stress Test in the mod list). They apply when the game loads: to change one, save, quit to the main menu, change it and load again. All start off or at the default, so the game is unchanged until you pick them.

• Top bar button (Text / Icon, default Icon): the button that opens the window. Icon: a gauge icon on a dark tile, like the game's data layers button. Text: the word "Debug".
• No costs (Off / On, default Off): building and vehicles cost nothing (the game's own noCosts setting, as in the official No Costs mod).
• Sandbox mode (Off / On, default Off): the game's sandbox mode with the town editor and industry menus, as in the official Sandbox mod.
• Vehicles never expire (Off / On, default Off): no vehicle model goes out of production, as in the official "No end year for vehicles" mod.
• No noise and pollution (Off / On, default Off): vehicles emit no noise or pollution, the game stops updating the emissions of industries, stations, depots and warehouses (existing ones keep their current value, new industries start at zero), and noise and pollution no longer lower town ratings (towns given their own sensitivity in the town editor or the Game tab keep it).
• Sim person trip recalculation (x1 / x2 / x5, default x1): how often town residents pick new destinations. x1 is the game's default; higher means more trips and more simulation load.
• Town development interval (Default / Fast / Very fast, default Default): how often towns grow. Default is the game's own interval (60), Fast is 15, Very fast is 5.
• Car traffic (Default / Drive: destinations / Drive: all town buildings, default Default): experimental, for testing only. Town buildings no longer allow walking or lines (public transport) as a way to travel, so more trips go by car. Drive: destinations changes shops and workplaces; Drive: all town buildings changes homes too. It changes the town buildings in your save as they are built or rebuilt (use Towns, Grow to rebuild a town right away); after you remove the mod they return to normal only when rebuilt. Check the effect with Scan on the Traffic tab (Last trip mode: DRIVE / WALK / LINES).
• Town building capacity (x1 / x2 / x4, default x1): experimental, for testing only. Multiplies the residents and workers of every town building (not the goods it needs), so more people make more trips, including between towns. Same as Car traffic: it changes buildings as they are built or rebuilt and they return to normal only when rebuilt. x4 can slow the game down a lot.
• Show probe tab (developers) (Off / On, default Off): adds the Probe tab with the in-game experiments the tool was built from. Each of its buttons changes your save; for mod developers only.

For more car traffic between towns (for example to test roundabouts and interchanges): Car traffic = Drive: destinations and Town building capacity = x2, then Towns, Grow once, and the Junction test's Traffic = Bus lines for guaranteed traffic through every junction.

Notes

• Hidden notifications and the town rating sensitivities are stored in the save: uncheck "Hide all notifications" and press "Restore defaults" before removing the mod.
• Stops and depots built by auto bus lines stay when the lines are removed; bulldoze them by hand if needed.
• Added vehicles and bus lines are remembered for this session only: after a reload the remove buttons no longer know them.
• All settings take effect when the save is loaded, so changing one needs a reload. "No noise and pollution" stores nothing in the save: turn it off (or remove the mod) and reload, and vehicles, the emissions script and the default town ratings are back to normal.
• Look for [SQST] lines in stdout.txt (in the game's crash_dump folder) for what each action did and how long it took.

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Changelog

Revision 3 (2026-10-13)

• The top bar button now has the same spacing as the game's data layers button and other mods' buttons, so a row of buttons looks even.
• New: Bench > Micro: a small bench for one-off tests, run like the sheets (now: 2-, 3- and 4-lane roundabouts, each built as eight twins: the game default, Smart Lanes and Smart Lanes' six ring lane layouts, towns of about 600 people; the report ranks the layouts); sheet 1 is now roundabouts only (11 sets: the lane drop test compared identical lanes and is gone); zone ids name their sheet.
• New: Bench > Sheet 4: one quick set each of 2-, 3- and 4-lane roundabouts (the 2-lane one with one-lane town streets as arms), each built twice: as players have it, with the game default and Smart Lanes, and with an extra ring node half way between the arms, with the game default and Smart Lanes' spiral that moves traffic into the inner lane at those nodes (on the 2-lane ring also a layout that makes every lane change, in and out, only there). The report names each twin's ring and ranks them per roundabout; towns of about 400 people. Needs the current Roundabouts & Interchanges and Smart Lanes.

Revision 2 (2026-10-11)

• The game's data layer windows (Infrastructure, Traffic and the others) now open below the top-left button row instead of under its buttons.
• New: mod setting "Top bar button": the button that opens the window is now a gauge icon on a dark tile that stays pressed while it is open, like the game's data layers button (default), or the word "Debug" as before.
• Fixed for PlayStation 5: the window no longer crashes the UI when it opens; a window option the platform doesn't support is left out.
• New: Towns tab "Test grid": identical towns at exact grid positions, for traffic tests between towns.
• New: Towns tab "Remove towns": the nearest town, the grid towns or all towns.
• New: Towns tab "Remove all roads".
• New: Towns tab "Junction test" (needs Roundabouts & Interchanges): every junction type between test towns, for real traffic tests. Roads are large country roads, highway arms stay highways; "In line" adds as many extra junctions as fit on every route, each a different layout; spacing up to 8 km.
• New: Test grid and Junction test "Streets": towns on a grid of wide 4-lane streets, optionally locked against town changes.
• New: warnings (no room for a grid, a busy job, refused junctions) are shown in a dialog.
• New: Towns tab "Crossing test": 4 towns and a 3 x 3 grid of long roads between them (3, 2 and 1 lanes each way, crossing in all 9 combinations, collector roads with T junctions), traffic lights off by default, for lane rules at ordinary junctions with real traffic.
• New: Junction test "Lights": the game's automatic traffic lights or none.
• New: Clear traffic "Where": in towns only, or outside towns only.
• New: Keep traffic cleared can also repeat every 60 or 120 seconds.
• Changed: Remove all roads and Remove towns wait for a running Junction test, Crossing test or Showcase (a busy dialog), so a test is never half removed while it builds.
• New: Towns tab "Showcase" (needs Roundabouts & Interchanges): every interchange and roundabout type with random settings from a seed, on an interchange line, a roundabout line and groups of one roundabout with a town on every arm.
• Changed: faster Junction test and Showcase builds: all junctions are placed back to back, then one short pause before they are linked, instead of a pause after every junction.
• Changed: a highway's link joins its town through a large 4-lane street, and links prefer the town's large streets, so highway traffic no longer squeezes through a small town street.
• New: Junction test and Crossing test "Traffic": with Bus lines, bus lines between the test's towns are added after the build, so buses drive through the junctions (Junction test: two crossing lines per junction; Crossing test: straight across the grid and turning). A one-line summary of what was built is written to the window's log. The bus lines come after the build, which costs money: without "Keep balance" (Game tab) they are skipped below 1M.
• Changed: Showcase spacing follows the real size of every interchange and roundabout setting (ovals with splitter islands, Hamburgers and small Magic Roundabouts were placed too close); each junction's size is measured after it is built and written to the log.
• Changed: a Showcase town link refused with a collision is tried again to the nearest town street, along the arm first; highway links between two junctions copy the narrower highway of the two.
• Changed: Showcase group towns are matched to the directions their junction's arms really leave in; a town without an arm in its direction is linked to the nearest free arm.
• Changed: a Showcase junction refused with "Construction Not Possible" is tried once more with freshly drawn settings of the same type; the dialog lists it, the log keeps the refused settings.
• Fixed: bus lines that were not added (balance below 1M without Keep balance, no bus on sale, too many failed towns) were only written to the log; now a dialog says why and what to do. Junction test and Crossing test warn when Build is pressed with Traffic Bus lines and Keep balance off.
• Changed: a refused placement's log line names what it collided with (nodes, asset groups, fields, ...) instead of "other".
• Fixed: bus lines between test towns reuse a depot only on the same road network and never buy a bus that can't reach the line (a new depot near the first stop, else the line is given up; a bus that can't join its line is sold again). Depots keep 400 m from the map edge, and a depot whose street connection fails is removed again.
• Changed: the Showcase is one button: groups only (the interchange and roundabout lines are gone: towns 16 km apart sent no traffic across the map), with every interchange, roundabout and plain game crossroads / T-junction type in turn, small or medium towns close around each, as many as fit. A new seed per press, Keep balance switched on, bus lines always added. Each group is built as side-by-side twins with identical settings (Smart Lanes / game default, plus Smart Lanes light phases at lit plain crossings), and each group's zone and mode go to the log.
• New: with Smart Lanes enabled, the Showcase sends it the twins' zones before it builds anything and waits until Smart Lanes has them (at most 5 seconds): Smart Lanes then leaves the game-default twins alone and plans its light phases at the third twins. Remove all roads and Remove towns (grid or all towns) clear the zones again.
• Fixed: roads the mod builds (Junction test and Showcase links, bus stops, depot connections, locked grid streets) give every new or joined road node its lane setup. Nodes without one could crash the game at random.
• New: Traffic tab "Traffic log": every 10, 30 or 60 game seconds, the traffic of each Showcase twin, the whole map, the Showcase bus lines and the towns, as [SQST] FLOW lines in stdout.txt for an A/B comparison. The Showcase also stores its twin names with the zones it sends Smart Lanes, so the log knows the twins again after a reload.
• New: Towns tab "Lights showcase": one button, lit crossroads and T-junctions only (1 to 3 lanes each way per arm), every shape three times, each built as three identical twins (Smart Lanes, game default, Smart Lanes exit-lane fan), medium towns grown to about 400 people after the links, no bus lines; the traffic log restarts on it like on a new Showcase. The changes below describe how it works now.
• Changed: Showcase and Lights showcase towns stay inside their street grids, so traffic reaches each junction only through the grid. Every town street is locked against town changes: the grid (now built locked), the town's own first streets and the link roads to the junction; corner stubs no link uses are removed. After the links every Showcase town grows x10 in 3 passes (Lights showcase towns: x3 in one, see below) with its buildings shifted to the higher levels, for a dense centre; after each pass any street the town still built is locked too, and the log counts streets and houses outside the grid (outside_streets=, houses_outside=).
• Changed: "Wide grid, locked" locks the grid in batches of at most 100 streets, each sent again once if the game refuses it.
• Changed: the Lights showcase uses an exact square layout: every crossing at 90 degrees and lined up with the map, a town straight north, east, south and west of it at one distance, and each link one straight road into the middle of the town's facing side (the grid now always has a central street both ways). Crossing arms are country roads (still 1 to 3 lanes each way).
• Fixed: a Showcase link could end on a corner of a neighbouring town, leaving its own town unlinked. A link now always ends on its own town's streets; if it can't, the arm stays unlinked, the log says why and the set is marked as not comparable (match=no reason=link).
• Changed: Showcase link roads are country roads with the arm's lanes, and the outer ring of a locked street grid is a country road, so towns no longer build houses along the links or outside their grid. Every street around a Showcase junction is locked too, so towns can't grow streets off the crossing. A refused link logs what it collided with.
• Changed: the Lights showcase builds every junction shape on one map (three sets each, twins Smart Lanes, game default and Smart Lanes exit-lane fan) instead of one shape per press. Its towns grow once after the links instead of in 3 passes (to about 400 people each, every town from its own capacity; the log lists each town's population), and it builds no bus lines (the towns' own traffic). A 16 km map now takes about 2 minutes instead of 10 to 15.
• Changed: faster Showcase, Lights showcase, Junction test and Crossing test builds: the street grids go up ten per build, every town in one command, the street locks of all towns together in batches of 100, and the Showcases' town links up to eight per build when they are far apart. Whatever the game refuses in a batch is built again one by one, and the log names the piece that failed. Each Showcase logs how long each phase took and the total minutes.
• Changed: Showcase towns are named after their test instead of "Grid S35": the junction type, set, the side of the junction they lie on and the twin, e.g. "Parclo 3 N (Smart lanes)"; Lights showcase towns by twin, set and side, e.g. "Smart lanes 1 N", "Game default 1 E", "Smart phases 1 S", "Kerb locked 1 W". Remove towns > Grid towns still finds them, the old "Grid S" towns of earlier saves too, and every town a test made in this session.
• Changed: every town of a Showcase has the same size: all medium in the Showcase (no more small ones) and in the Lights showcase (no more large ones), which instead grows its towns once, denser and taller inside their grids. A 16 km map now holds 6 Lights showcase sets instead of 4. Seeds logged before this change build a different layout.
• Fixed: Showcase bus lines failed after the towns grew (every depot spot was built up). Each route's bus depot is now built before the towns grow, and the lines use it.
• Changed: Lights showcase town entries are no longer the bottleneck: the links are large country roads (3 lanes each way), and each town is entered through a three-lane roundabout (two-lane where three does not fit) at the middle of its grid's side instead of a crossroads (from 1940; Roundabouts & Interchanges not needed). Every twin gets the same entries; a set whose entries differ is marked as not comparable in the log.
• Changed: the traffic log reads every car on the map instead of the first 3000 (it reads fewer, spread over the map, only when a sample could not finish in time), and measures each junction together with its approach roads, with the queue on each approach.
• Fixed: the towns' "houses outside the grid" count in the log could count buildings without a finished footprint as outside; their spot now comes from the building itself.
• Changed: the traffic log also counts the cars through each junction per game minute (thru) and splits each arm's queue into the side towards the junction and the side away from it; the flow report compares both per pair and across every shape. The rig's roads join with every lane connected where the lane count changes.
• New: Towns > Bench: one button per test sheet runs a whole Smart Lanes test on its own: it clears the map, sets the year to 1950 if earlier, builds every test of the sheet as twins (game default / Smart Lanes / a Smart Lanes test mode) with a town only on the arms that need traffic, packed tightly onto a 16 km map, waits for Smart Lanes, records 20 game minutes of traffic at 2x and takes a screenshot of each test. Sheet 1: 2-lane roundabouts (also with the lights Smart Lanes would remove kept) and lane drops; sheet 2: channelized T-junctions and diamond interchanges; sheet 3: lit T-junctions and crossroads (also with the kerb turn locked). The make bench report (in its source repository) turns the log into a results draft.
• Changed: the traffic log counts the cars through each junction by position (on an approach road towards the junction at one sample, gone from it at the next), as the paths' street ids could not be read; the path count stays as thru_path. Interchange approaches are measured 50 m wide (both carriageways).
• New: the crossing construction's Straight shape (a road whose lanes change at one node), used by the bench's lane drop test.
• Changed: the bench checks every built twin presents what its test measures (the lane drop's lane change, the roundabout's ring) and leaves a set out of the comparison when not; it records without reading the drivers' paths (the count by position matched the path count within 1 %), and the traffic log names the phase of each sample's slowest frame.

Revision 1 (2026-10-10)

• Initial release.