The H42 sign identifies average speed control in Portugal, indicating that a stretch of road is subject to electronic enforcement. According to the National Road Safety Authority (ANSR), these devices measure the time a vehicle takes to travel a specific distance between two control points, then calculating the average speed by dividing the distance by the elapsed time. For example, travelling 10 kilometres in six minutes corresponds to an average speed of 100 km/h.
The measurement of average speed is covered by Ordinance No. 352/2023, which approves the metrological control regulations for enforcement equipment. The article clarifies that it is not necessary to maintain a strictly constant speed during the journey, and it is essential to respect the applicable limits and adapt driving to road, traffic and visibility conditions.
The H43 sign differs from H42 by measuring instantaneous speed at the moment the vehicle passes the control location, that is, at a specific point. Thus, while H43 is associated with speed at a point, H42 corresponds to the average calculated along a route between two enforcement points.
The article warns that reducing speed only near the second control point does not guarantee that the average stays within the limit, as the result depends on the entire time spent travelling the section, including the portion covered before that reduction. The National Speed Control System devices are always signposted, so that drivers know the control locations in advance.
