Smart Lanes

Smart lanes + Smart lights. Roundabouts, slip-lane junctions, crossroads and T-junctions get lanes that fit them right after you build them, and lit crossroads and T-junctions can get an improved 4-phase light plan: one long green per road with every lane at once, and a short pedestrian phase before the cross road goes.

Automatic light timing keeps giving the green to the roads where cars are waiting, and Record traffic counts the vehicles at any junction or roundabout, so you can see what a change did.

Tested in game, side by side against the game's own lanes and lights: Smart lights moved 23-26 % more cars a minute through busy lit crossroads than the game's phases (6 of 6 sets), and smart lanes put 16 more cars a minute through two-lane roundabouts.

Features

• Roundabouts: entry, ring and exit lanes line up one to one, on the game's roundabouts, those from Roundabouts & Interchanges and rings you draw yourself. Wide rings get an exit-only outer lane; small 2-lane rings with town street arms get extra nodes between the arms, so cars change lanes there instead of at the arms.
• Slip lanes and ramps: where a slip lane or ramp leaves or joins a road, lanes are matched without crossings; through traffic keeps its lanes.
• Crossroads and T-junctions: turning traffic never cuts across the through lanes, lanes are never squeezed inside the junction, and turns served by a slip lane are left to it.
• Lane drops and gains: where a road changes width, the curb lane ends or starts without lanes crossing.
• Bus lanes: the car lanes get smart lanes, and a bus lane may turn every way the cars of its road can, into the next bus lane where there is one. At traffic lights a new bus turn goes with its bus lane's green, and a turn that would need other light phases is left out: phases stay as they are. Car lanes never lead into a bus lane.
• Free curb turn: at traffic lights the turn toward the curb also gets green in phases where nothing crosses its path (or always, see Settings).
• Smart lights: select a lit crossroads or T-junction and press Smart lights to plan its phases around its lanes as they are now, including lanes you set by hand. Once applied the button hides and the status shows "√ Smart lanes | √ Smart lights".
• Re-time: measures a lit junction's traffic for about 3 game minutes, then sets its cycle and green times to fit: more green for the busier road.
• Keep timing adjusted (Yes / No): re-times the junction by itself over a long game as its queues change, also with the tool closed.
• Automatic light timing: set it to All lights and every traffic light on the map is kept adjusted, also ones built later; choose No at a junction to leave it out.
• Record traffic: counts the vehicles through any junction or roundabout for up to 20 game minutes and shows vehicles per minute, live. Up to 20 can record at once; a new recording shows the previous result below it.
• Smart Lanes tool (Roads, Tools, next to the Crossing Tool): click a junction, a roundabout or a street to select it, Shift+click to add more (up to 60 junctions), then press Smart lanes. Reset brings back the game's lanes and lights and keeps them: the status reads "Game default (locked)".
• Light settings in game: the light settings can be changed for the current game on the left of the Smart Lanes tool and of the game's Crossing Tool.
• Welcome on first load: offers to convert the junctions already on the map and to switch all lights to automatic timing. Save first; it asks once per game.
• No lights at roundabouts and ramps: the game's automatic lights are switched off where traffic should only give way or merge.

Settings

• Apply automatically to new roads (On / Off, default On): smart lanes right after you build; Off leaves it to the tool.
• No lights at roundabouts and ramps (On / Off, default On): no game lights at roundabouts, slip lanes and ramps.
• Bus lanes (Any direction / Keep as built, default Any direction): Keep as built leaves bus lane connections as the game or you made them.
• Bus lanes at traffic lights (Stop at red / Skip red lights, default Stop at red): Skip red lights lets buses in a bus lane drive through every light phase in which no crosswalk is green, at the crossroads and T-junctions Smart Lanes handles. Buses do not give way to cross traffic; trams in a bus lane go with them. After changing it in the game, Apply to all junctions (under the setting in the tool) sets every lit junction with a bus lane at once.
• Free curb turn at traffic lights (Off / When safe / Always, default Always): when the curb turn may go.
• Light phases (Game default / Smart Lanes, default Game default): Smart Lanes gives every lit crossroads and T-junction it handles the Smart lights plan.
• Automatic light timing (Junctions I choose / All lights / Off, default Junctions I choose): where Keep timing adjusted runs; Off stops it everywhere, with no traffic counting.
• Keep timing adjusted: check interval (x0.5 / x1 / x2 / x4, default x1): how often a junction is checked.
• Debug: performance log (Off / On, default Off): timing lines in the game's log, for tracking down slowdowns.

Tested against the game's lanes

Each junction built twice side by side, once with Smart Lanes and once as the game makes it, each fed by its own towns for 20 game minutes.

• Lit crossroads, Smart lights vs the game's phases: +23 % and +26 % cars a minute (2 and 3 lanes each way), 6 of 6.
• Slip-lane T-junction: 13 to 42 km/h, +27 % cars, 9 of 9 (mostly from switching off the game's lights at the slip lanes).
• 2-lane roundabout: +16 cars a minute (+27 %), 9 of 9.
• Lit T-junction: +48 % speed, 9 of 9. Lit crossroads lanes: +27 % speed, 14 of 15.
• Diamond interchange: +55 % speed, 5 of 6.

Notes

• Pairs well with Roundabouts & Interchanges, a separate mod of mine that builds complete roundabouts and interchanges; Smart Lanes sets up their lanes as soon as they are placed. Each works on its own.
• Junctions with five or more roads, single-lane rings and rings with a bus lane are left as the game builds them. You can still change any junction with the Crossing Tool.
• Safe to add to an existing save. Safe to remove: its lane settings are ordinary junction settings and stay in the save.

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Changelog

Revision 12 (2026-10-28)

• New setting Bus lanes at traffic lights: Skip red lights lets buses in a bus lane drive through every light phase in which no crosswalk is green, at the traffic lights Smart Lanes sets. Trams that share a bus lane skip the red with them. Buses do not give way to cross traffic. Default: Stop at red (nothing changes).
• New: after you change that setting in the game, Apply to all junctions sets it at once at every junction with traffic lights and a bus lane, whatever its shape. Junctions you reset with the Smart Lanes tool are left alone.
• Fixed: Smart Lanes' own light changes no longer count as newly built lights for Automatic light timing.

Revision 11 (2026-10-27)

• New: with Smart lights, a turn toward the curb from a lane that also goes straight now also gets green in the other road's phase when nothing crosses its path, e.g. into a T-junction's side road while the side road has green. Lights you have not changed by hand can get it once: a window asks when you load a save.
• Fixed: at lit junctions with tram tracks, Smart lights could set the wrong turns red (for example the main road's turn into a side road). Lights you have not changed by hand are corrected automatically when you load a save.
• New: bus lanes turn every way. At the junctions Smart Lanes handles, a bus lane gets a turn into every road the cars of its road can turn into, into that road's bus lane where it has one. At traffic lights the new turns go with their bus lane's green, and light phases never change for them. Junctions whose lanes Smart Lanes already set get the missing bus turns too: the tool shows "Smart lanes, bus turns missing" and Apply adds them. The setting Bus lanes: Keep as built leaves bus lane connections as before.
• Changed: with Roundabouts & Interchanges' Lock built roads on, Smart Lanes waits until a new roundabout's roads are locked before it sets the lanes.

Revision 10 (2026-10-19)

• Fixed (PlayStation 5): the welcome window on a new or first-loaded game no longer reloads the UI with "attempt to call field 'makeInfoHint' (a nil value)". The PS5 version of the game lacks a function the window used; it now builds that note itself.
• Controller (PlayStation 5): the welcome window takes the controller focus when it opens, the d-pad moves between its checkboxes and buttons, and the back button (Circle) answers Not now.

Revision 9 (2026-10-17)

• New: Automatic light timing can be Off: no junction's timing is adjusted and no traffic is counted. Junctions you chose stay chosen for when you switch it back on.
• New: Re-time can measure up to 5 junctions at once.
• Faster: with no junction set to Keep timing adjusted, the light timing does almost nothing in the background, and Smart Lanes reads its saved data less often.
• Faster with All lights: the map is searched for new lights once an hour of game time instead of every 5 minutes (lights you build are picked up at once), junctions with little traffic are checked less often, and heavy steps are spread over more frames. In tests the worst frame from light timing dropped by about 85%.
• Smoother: many traffic recordings or Re-times at once no longer cause a short stutter when they take a sample or save a checkpoint.
• Changed: building a road no longer changes the lanes of a nearby junction it does not connect to (roundabouts are still set up whole).
• Changed: a junction Smart Lanes does not handle now says why in plain words, for example "not handled: a road has only bus lanes".
• Changed: a grayed button's reason (for example Re-time with 5 junctions measuring) now also shows in the status text.

Revision 8 (2026-10-16)

• New: Smart lights button: Smart Lanes light phases for a lit crossroads or T-junction, planned around its lanes as they are now (hand-set lanes kept). Once set, the status shows "√ Smart lanes | √ Smart lights".
• Changed: Smart Lanes light phases give each road one long green for both directions, every lane at once, then a short pedestrian phase; in tests 23-26 % more cars a minute than the game's phases. Shapes the plan can't handle keep the game's phases.
• New: with Light phases on Smart Lanes, a traffic light you switch on later gets Smart Lanes phases right away.
• New: Re-time button: sets a lit junction's cycle and green times from about 3 game minutes of measured traffic.
• New: Keep timing adjusted (Yes / No) re-times a junction by itself over a long game; settings "Automatic light timing" and "Keep timing adjusted: check interval".
• New: Record traffic button: vehicles per minute at any junction or roundabout, up to 20 at once, with the previous result shown.
• New: light settings can be changed for the current game in the Smart Lanes tool and the Crossing Tool; a welcome window on first load offers to convert existing junctions.
• Changed: Apply is now Smart lanes; buttons sit in rows and show only where they do something; Reset also restores the game's light phases; reset junctions read "Game default (locked)".
• Changed: the free curb turn only frees a lane that turns and nothing else.
• Changed: 2-lane roundabouts whose exits all have two or more lanes get matched lanes instead of the exit-only outer lane (21 % more cars in a test).

Revision 7 (2026-10-14)

• Changed: a Reset with the Smart Lanes tool now sticks: later builds nearby no longer give the junction smart lanes again.
• Changed: a turn across traffic into a road with a street stop or the next junction within 80 m may use every lane of that road, so buses reach curb stops without changing lanes.
• Changed: American English spelling (the setting is now "Free curb turn at traffic lights").

Revision 6 (2026-10-14)

• New: 2-lane roundabouts with one-lane exits get no lane change at the arms; cars change lanes at nodes Smart Lanes adds between the arms (in tests 55 % faster, 47 % more cars than the game's lanes).
• New: the Smart Lanes tool shows those nodes' lane changes, and Reset gives them straight-on lanes.
• New: junctions with bus lanes get smart lanes for their other lanes; bus lane connections and the junction's lights stay as they are.

Revision 5 (2026-10-13)

• Changed: plainer tool texts: reasons in words, no internal ids, "Custom" is now "Game or custom lanes", status lines are plain text.
• Changed: one Apply button instead of Apply to junction and Apply to roundabout; clearer tooltips.
• Fixed: roundabouts get the same lanes whatever order their arms were built in.

Revision 4 (2026-10-11)

• New: smart lanes for crossroads and T-junctions, lane drops and gains, exit lanes before off-ramps and on-ramps into roundabouts.
• New: settings "No lights at roundabouts and ramps", "Free curb turn at traffic lights" and "Light phases"; map areas other mods and tests can mark for Smart Lanes.
• New: the tool selects streets and several junctions (Shift+click, up to 60); faster tool and a smoother automatic pass after big builds.
• Fixed: a crash at junctions with traffic lights, ramps on two-way roads turning across oncoming lanes, and a script error at junctions of one-way roads all leading the same way.

Revision 3 (2026-10-10)

• New: translations into 12 languages; the mod follows the game's language setting.

Revision 2 (2026-10-10)

• New: an optional performance log ("Debug: performance log", Off by default); hover diagnostics are logged only with it On.

Revision 1 (2026-10-08)

• New: automatic lane assignment for roundabouts (matched entries and exits, exit-only outer lane) and slip-lane junctions.
• New: the Smart Lanes tool next to the Crossing Tool, with lane status, Apply and Reset.