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Drivers travelling on Indian highways and expressways may notice that the permitted speed changes from one road to another. While some modern expressways allow passenger cars to travel at up to 120 km/h, speed limits on several national and state highways can be 100 km/h or even 80 km/h. These differences are not arbitrary. They are determined by road design, traffic conditions, vehicle type and safety considerations.

 

One of the biggest factors behind highway speed limits is the way a road is designed. Expressways are generally access-controlled roads, meaning vehicles and pedestrians cannot enter the carriageway from random points. They have designated entry and exit locations, reducing the possibility of unexpected encounters with local traffic, pedestrians or animals. This controlled environment makes higher speeds possible. On the other hand, conventional highways may pass through villages, towns and busy intersections. They can also have frequent cuts and access points where vehicles may suddenly enter the road. As a result, lower speed limits help reduce the risk of collisions.

Road geometry is another important consideration. Engineers calculate how safely vehicles can negotiate curves at different speeds. Roads may be designed with appropriate banking or superelevation to help vehicles remain stable while turning. Modern expressways generally feature gradual curves and better visibility, allowing drivers to anticipate changes in the road well in advance. Roads with sharper bends, slopes, bridges or limited visibility may require lower speeds because sudden braking or steering at high speed can increase the chances of losing control.

The permitted speed is not necessarily the same for every type of vehicle. According to the information cited in the source article, passenger cars can have a maximum limit of 120 km/h on eligible expressways, while heavy vehicles such as buses and trucks may have lower limits. The reason is straightforward: heavier vehicles generally require more distance and time to stop. Their larger size and weight can also make sudden manoeuvres more difficult.

The number of lanes, traffic volume and overall road environment can also influence speed restrictions. A wide, access-controlled road with relatively predictable traffic can safely support higher speeds than a busy highway with frequent intersections and mixed road users. Drivers should therefore treat speed-limit signs as important safety information rather than simply as rules designed to prevent speeding fines. The posted limit reflects the conditions for which that particular section of road has been assessed.