Type of Intersection and It's selection

• Intersection Design : Intersections connect roads and are designed based on vehicle dimensions, speed, and operating characteristics (e.g., articulated or rigid, low profile, long axle spacing). They must provide sufficient pavement for vehicles to transition between roads. The design begins with determining the kerb return radius to smoothly connect the major and minor roads, applicable to both urban and rural roads despite the absence of kerbs in rural settings. Vertical geometry is then integrated with the adjoining roads' design.

 

• Basic Turn Treatment : Basic (BA) turn treatments, including BAR (right-turn) and BAL (left-turn) treatments, are simple and cost-effective designs for low-traffic, two-lane roads where channelised treatments are unsuitable. They feature widened shoulders to facilitate vehicle movement, appropriate corner radii, and clear delineation to ensure safety and functionality. On rural roads, BAR treatments allow slowed vehicles to pass turning traffic on the left, while BAL treatments provide space for turning vehicles to clear the carriageway. Sealed shoulders are preferred for maintenance and safety, as research indicates BAR treatments have significantly higher rear-end crash rates compared to channelised right-turn treatments, with crash rates decreasing as median width increases.

 

 

 

• Auxilary Lane Turn Treatment : Auxiliary (AU) turn treatments improve safety on high-speed roads by providing short auxiliary lanes, including AUR (right-turn) and AUL (left-turn) treatments on major and minor roads. AUR treatments, though safer than basic treatments, are less safe than channelised treatments (CHR) and are less preferred for new unsignalised intersections. These treatments allow vehicles to bypass turning traffic, require sealed surfaces, and must be clearly distinguishable from overtaking lanes. Common in rural areas with moderate turning traffic and low through-traffic, AUR and AUL treatments feature painted stripes or indented lanes, offering a cost-effective solution when factoring long-term crash reduction benefits.

Channelised turn (CH) treatments : It separate conflicting vehicle paths using raised, depressed, or painted medians and/or islands, often paired with auxiliary lanes for clarity and safety. They include CHR (right-turn) and CHL (left-turn) treatments on major and minor roads. CHR treatments reduce rear-end and overtaking crashes by guiding traffic past turning vehicles, offering consistent intersection layouts, pedestrian refuges, and longer design lifespans compared to AUR treatments. CHR(S), a shorter variant, uses line marking to safely remove stationary turning vehicles from through traffic, suitable for low to moderate traffic volumes. These treatments enhance safety, particularly on high-speed roads.

• Warrants for BA, AU, and CH turn treatments : it guide the selection of appropriate layouts for major roads based on design speed and traffic conditions. CHR and CHL treatments are generally preferred for ensuring clear sight lines and safety at intersections, although many existing intersections on low-volume roads lack the infrastructure to meet these standards. Guidance in Figure 2.26 includes graphs for selecting turn treatments based on design speeds: high-speed rural roads (≥ 100 km/h), higher-speed urban or lower-speed rural roads (70–100 km/h), and urban roads (< 70 km/h).