Types of intersections

The number of conflict points in an intersection at which road users may collide is important for safety. The fewer potential conflict points, the safer the intersection will be. That is one of the reasons why roundabouts are safer than intersections (Figure 2). Furthermore, in an inherently safe traffic system it must be impossible for road users with large differences in speed and mass to meet; such crashes can be very severe (see also SWOV Fact sheet Speed and speed management)

When conflicts can occur, it is important to reduce their severity by setting a safe speed limit. Table 1 shows the safe speed limits for encounters between certain types of road users. It can be seen, for example, that 30 km/h is the safe speed limit for encounters between different types of road users.

Safe speeds can be brought about by setting a safe speed limit and by infrastructural measures. At intersections physical speed-reducing measures such as roundabouts, speed humps and raised intersections can be used. Furthermore, the desired driving speed can be evoked by consistency and continuity in road design. This will ensure that road users recognize the types of roads and intersections and know what they are expected to do (Wegman & Aarts, 2006). For more information about speed management see te archived SWOV Fact sheet Measures for speed management. More about recognizability can be found in SWOV Fact sheet Predictability by recognizable road design (archived).

For certain intersections and roundabouts, the choice is made to use traffic signals to manage the traffic. Three criteria are used to determine whether or not traffic signals need to be installed (CROW, 2006): traffic volume, time loss and safety in numbers of crashes. Well-designed traffic management results in efficient time distribution among road users and can, for instance, give priority to public transport (CROW, 2006). Traffic signals use time to separate traffic; they take care that, for example, the two conflicting directions at an intersection do not get a green or amber signal simultaneously. Furthermore, the time lapse between the end of the amber signal for the one direction and the start of the green signal for the other direction must be sufficiently long (CROW, 2006) .

There are several types of traffic signal, see Table 3. The most suitable type is determined by the traffic situation. In general, traffic signals do not improve road safety (Ogden (1996) in Hummel, 2001). This is due to the fact that the traffic is not separated location-wise but time-wise, which means that red light violations can still result in crashes. Because in those cases speeds are often high, this leads to serious conflicts. Rear-end collisions can also occur when a driver continues at the same speed while the vehicle in front slows down (Kennedy & Sexton, 2009).

There are different possibilities to handle slow traffic when traffic signals are used a VRI. Non-conflicting bicycles in parallel directions can get green at the same time as motorized traffic. It is also possible to give all cyclists the green light simultaneously, while the other traffic has to wait for red (CROW, 2006). The safety effects of the different methods are unknown.

There are numerous types of intersections in the Netherlands. In an inherently safe road traffic, however, a limited number of intersection types for intersections between different road types is preferable. These preferred intersection types sometimes differ from the recommendations in the Dutch design manuals. Inherently safe intersection types make allowance for safe speeds to avoid serious conflicts, transverse conflicts and frontal conflicts, or to reduce the severity of the consequences. At a 30 km/h speed limit, slow traffic and fast traffic can be allowed to mix. At higher speeds, this is no longer permissible.

When the choice is between the construction of an intersection or a roundabout, the roundabout is preferred for security reasons. Intersections are preferably not regulated by traffic signals; high driving speed can result in very serious conflicts in the case of red light negation. Uniformity of intersection types is important in order to make them recognizable and predictable for road users and thus encourage the desired traffic behaviour.