Average speed control sections

_{Last updated: September 14, 2026 | 3 minutes read}

An average speed control section is an enforcement zone bounded by an entry gantry and an exit gantry, where the average speed between the two gantries is measured rather than the instantaneous speed. The SDK reports the driver's progress and running average inside such a zone through SpeedSectionAlarm.

For instantaneous speed limit monitoring, see Speed warnings.

Listen for section events

The section callbacks carry no arguments and have to read the sections back from the service. Declare the service before the listener and create it afterwards, which is the pattern the SDK itself documents:

AlarmService? alarmService;

AlarmListener alarmListener = AlarmListener(
    onApproachingSpeedSectionAlarms: () {
        for (final section in alarmService!.approachingSpeedSectionAlarms) {
            showSnackbar("Section control ahead, limit ${section.speedLimit} m/s");
        }
    },
    onEnterSpeedSectionAlarms: () {
        showSnackbar("Entered ${alarmService!.speedSectionAlarms.length} section(s)");
    },
    onTravelSpeedSectionAlarms: () {
        for (final section in alarmService!.speedSectionAlarms) {
            showSnackbar(
                "Average ${section.speedAvg} m/s, ${section.remainingDistance} m left");
        }
    },
    onExitSpeedSectionAlarms: () {
        for (final section in alarmService!.exitedSpeedSectionAlarms) {
            showSnackbar("Left section, final average ${section.speedAvg} m/s");
        }
    },
);

alarmService = AlarmService(alarmListener);

Enable section alarms

Section alarms are disabled by default and require the safety cameras overlay to be present in the alarm service overlays collection:

final service = alarmService!;

service.overlays.add(CommonOverlayId.safety.id);
service.enableSpeedSectionAlarm = true;

Check the current state with service.isSpeedSectionAlarmEnabled.

warning

Section alarms are produced only while navigating with a route. They are not emitted in free drive.

Read the active sections

Read the corresponding getter on AlarmService to obtain the sections each notification refers to:

Callback	Getter to read
onApproachingSpeedSectionAlarms	approachingSpeedSectionAlarms - sections coming up within the configured alarmDistance.
onEnterSpeedSectionAlarms	speedSectionAlarms - sections the vehicle is currently inside.
onTravelSpeedSectionAlarms	speedSectionAlarms - the same sections, with updated progress.
onExitSpeedSectionAlarms	exitedSpeedSectionAlarms - sections just left behind.

info

approachingSpeedSectionAlarms and exitedSpeedSectionAlarms are guaranteed not to be empty when read from their own notification.

speedSectionAlarms carries no such guarantee: it returns the sections currently active, and an empty list when none are. Iterate it rather than indexing into it.

warning

Overlay-based alarms need an active GemMap, and the loaded map style must contain the safety overlay. Without both, the section alarms do not work correctly.

SpeedSectionAlarm

Property	Type	Description
entry	OverlayItem	The section entry gantry overlay item.
exit	OverlayItem	The section exit gantry overlay item.
totalDistance	int	Total enforced section length, in meters.
remainingDistance	int	Remaining distance to the exit gantry, in meters.
speedLimit	double	Enforced section speed limit, in meters per second.
speedAvg	double	Running average speed since the entry gantry, in meters per second.

Compare speedAvg against speedLimit to warn the driver while there is still distance left to compensate:

for (final section in alarmService!.speedSectionAlarms) {
    if (section.speedAvg > section.speedLimit) {
        showSnackbar(
            "Over the section average, ${section.remainingDistance} m to the exit gantry");
    }
}